cellulose microfibril

A microfibril composed of cellulose arranged in orthogonal layers. Cellulose is a straight chain polysaccharide composed of B(14) linked glucose subunits. It is a major component of plant cell walls. Higher plant microfibrils are about 10nm in diameter and extremely long in relation to their width. The cellulose molecules are oriented parallel to the long axis of the microfibril in a paracrystalline array, which provides great tensile strength. The microfibrils are held in place by the wall matrix and their orientation is closely controlled by the cell.


neck portion of tanycyte

biolink:CellularComponent biolink:AnatomicalEntity biolink:OrganismalEntity biolink:BiologicalEntity biolink:NamedThing biolink:Entity biolink:PhysicalEssence biolink:SubjectOfInvestigation biolink:ThingWithTaxon biolink:PhysicalEssenceOrOccurrent

Elongated portion of a tanycyte that sticks into the periventricular layer of neuropil where it appears to contact a blood vessel; characterized by numerous cytoplasmic extensions. A tanycyte is a specialized elongated ventricular ependymal cell that has processes that extend to the outer, or pial, surface of the CNS.


lamellipodium membrane

The portion of the plasma membrane surrounding a lamellipodium.


chloroplast chromosome

A circular DNA molecule containing chloroplast encoded genes.


plastid chromosome

A circular DNA molecule containing plastid encoded genes.


somatic spine

Spine emanating from the cell soma of a neuron.


glycinergic synapse

A synapse that uses glycine as a neurotransmitter.


platelet dense tubular network

A network of membrane-bounded compartments found in blood platelets, where they regulate platelet activation by sequestering or releasing calcium. The dense tubular network exists as thin elongated membranes in resting platelets, and undergoes a major ultrastructural change, to a rounded vesicular form, upon addition of thrombin.


cytoplasmic replication fork

The Y-shaped region of a cytoplasmic replicating DNA molecule, resulting from the separation of the DNA strands and in which the synthesis of new strands takes place. Also includes associated protein complexes.


host cell lysosomal membrane

The lipid bilayer surrounding the host cell lysosome and separating its contents from the host cell cytoplasm.


cellular birth scar

Crater-like ring of chitinous scar tissue located on the surface of the daughter cell, in budding fungi, at the site of separation from the mother cell. It is formed after the newly emerged daughter cell separates, thereby marking the site of cytokinesis and septation.


cell cortex of growing cell tip

Any cell cortex that is part of a growing cell tip.


posterior cell cortex

The region that lies just beneath the plasma membrane in the part of a cell that is closest to the posterior as defined by the developing, or existing, anterior/posterior axis.


dendritic spine cytoplasm

The region of the neuronal cytoplasm located in dendritic spines.


lateral cell cortex

The region directly beneath the plasma membrane of the lateral portion of the cell.


pole plasm

Differentiated cytoplasm associated with a pole (animal, vegetal, anterior, or posterior) of an oocyte, egg or early embryo.


apical cortex

The region that lies just beneath the plasma membrane on the apical edge of a cell.


presynaptic endocytic zone cytoplasmic component

The cytoplasmic component of the presynaptic endocytic zone.


dendrite cytoplasm

All of the contents of a dendrite, excluding the surrounding plasma membrane.


equatorial cell cortex

The region of the cell cortex in a mitotically dividing cell that flanks the central spindle and corresponds to the site of actomyosin ring formation that results in cleavage furrow formation and ingression.


presynaptic active zone cytoplasmic component

A specialized region below the presynaptic membrane, characterized by electron-dense material, a specialized cytoskeletal matrix and accumulated (associated) synaptic vesicles.


cell cortex of cell tip

The region directly beneath the plasma membrane at the cell tip. The cell tip is the region at either end of the longest axis of a cylindrical or elongated cell.


cell cortex region

The complete extent of cell cortex that underlies some some region of the plasma membrane.


medial cortex

A medial cortical band overlaying the nucleus which acts as a landmark for contractile ring positioning and plays a role in cell cycle regulation.


cytoplasmic region

Any (proper) part of the cytoplasm of a single cell of sufficient size to still be considered cytoplasm.


ooplasm

The cytoplasm of an ovum.


postsynaptic endocytic zone cytoplasmic component

The cytoplasmic component of the postsynaptic endocytic zone.


cell leading edge cell cortex

The cell cortex of the leading edge of a cell.


apicomedial cortex

The region that lies just beneath the plasma membrane in the middle of the apical edge of a cell.


basal cortex

The region that lies just beneath the plasma membrane on the basal edge of a cell.


plasma membrane bounded cell projection cytoplasm

All of the contents of a plasma membrane bounded cell projection, excluding the plasma membrane surrounding the projection.


anterior cell cortex

The region that lies just beneath the plasma membrane in the part of a cell that is closest to the anterior as defined by the developing, or existing, anterior/posterior axis.


ciliary plasm

All of the contents of a cilium, excluding the plasma membrane surrounding the cilium.


cell cortex

The region of a cell that lies just beneath the plasma membrane and often, but not always, contains a network of actin filaments and associated proteins.


neuron projection cytoplasm

All of the contents of a plasma membrane bounded neuron projection, excluding the plasma membrane surrounding the projection.


sarcoplasm

The cytoplasm of a muscle cell; includes the sarcoplasmic reticulum.


cell cortex of non-growing cell tip

The region directly beneath the plasma membrane at the cell tip at which no growth takes place.


dinoflagellate hypocone

The part of a dinoflagellate cell below the cingulum; also referred to as the posterior portion of a dinoflagellate cell. It is separated from the epicone by the cingulum.


nuclear outer membrane

The outer, i.e. cytoplasm-facing, lipid bilayer of the nuclear envelope; continuous with the endoplasmic reticulum of the cell and sometimes studded with ribosomes.


nuclear membrane

Either of the lipid bilayers that surround the nucleus and form the nuclear envelope; excludes the intermembrane space.


nuclear inner membrane

The inner, i.e. lumen-facing, lipid bilayer of the nuclear envelope.


germ tube

The slender tubular outgrowth first produced by most spores in germination.


virus tail, sheath

The external contractile envelope of the tail of some viruses. Its contraction ensures ejection of the virus DNA into the host cytoplasm.


lateral wall of outer hair cell

The lateral wall of an outer hair cell (OHC) is a unique trilaminate composite consisting of the plasma membrane, an underlying cytoskeletal network containing an actin-spectrin cortical lattice, and an adjacent system of circumferential lamellar organelles known as the subsurface cisternae.


pathogen-containing vacuole

A membrane-bound intracellular compartment that is formed upon internalization of a pathogen into a host cell, and in which the pathogen resides.


glial cell projection

A prolongation or process extending from a glial cell.


astrocyte end-foot

Terminal process of astrocyte abutting non-neuronal surfaces in the brain.


spiny bracelet of Nageotte

Paranodal terminations of Schwann cells that do not directly contact the paranodal axon membrane. Usually found in thicker myelin.


astrocyte projection

A prolongation or process extending from the soma of an astrocyte and wrapping around neurons.


glial limiting end-foot

Terminal process of astrocyte that extends to the surface of the central nervous system. Together, glial limiting end-feet form the glial limiting membrane or glia limitans.


terminal loop

Portion of myelin-forming Schwann cell consisting of terminal cytoplasmic extensions adhered to the axon at the beginning and end of the myelin sheath.


capitate projection

Simple or compound process of epithelial glial cells with a spherical head that inserts into photoreceptor axons. Capitate projections have only been observed in Brachycera (flies).


cerebellar granule cell to Purkinje cell synapse

A synapse of a granule cell fiber onto the dendrites of a Purkinje cell in cerebellum.


dense nuclear body

A location in the host cell nucleus where viral proteins colocalize late in infection prior to the onset of viral DNA synthesis. More than one site can be present simultaneously.


ventral disc microtubule array

A part of the ventral disc of Giardia species (trophozoite stage) consisting of a spiral array of microtubules linked to the ventral membrane. These microtubules form the base of the ventral disc dorsal microribbons that extend nearly perpendicular from the membrane.


chloroplast intermembrane space

The region between the inner and outer lipid bilayers of a chloroplast envelope.


Flemming body

A cell part that is the central region of the midbody characterized by a gap in alpha-tubulin staining. It is a dense structure of antiparallel microtubules from the central spindle in the middle of the intercellular bridge.


unencapsulated part of cell

The part of a cell encompassing the intracellular environment and the plasma membrane; it excludes any external encapsulating structures.


peroxisomal matrix

The volume contained within the membranes of a peroxisome; in many cells the matrix contains a crystalloid core largely composed of urate oxidase.


glyoxysomal lumen

The volume enclosed by the membranes of a glyoxysome.


glycosome lumen

The volume enclosed by the membrane of a glycosome.


lateral part of cell

The region of a polarized cell other than its tips or ends (in some cell types, one end may be called the apex and the other the base). For example, in a polarized epithelial cell, the lateral part includes the cell sides which interface adjacent cells.


lateral part of motile cell

The area of a motile cell perpendicular to the direction of movement.


ethanolamine degradation polyhedral organelle

An organelle found in bacteria consisting of a proteinaceous coat containing enzymes for the degradation of ethanolamine whose purpose is the protection of the rest of the cell from the toxic acetaldehyde product of the enzyme ethanolamine ammonia lyase.


Ubisch body

A small, granular structure that is found in the extracellular matrix of cell of the secretory tapetal layer that surrounds developing pollen grains. Ubisch bodies have a sporopollenin coat, are attached to the peritapetal wall, and may play a role in pollen development.


cytoplasmic microtubule plus-end

Any microtubule plus-end that is part of a cytoplasmic microtubule.


cortical microtubule plus-end

The plus-end of a cortical microtubule.


neutrophil extracellular trap

Extracellular microbicidal structure composed of nuclear chromatin, histones and granular antimicrobial proteins. Histones and several neutrophil granule proteins associated with the DNA framework damage entrapped microorganisms.


host cell chloroplast

A chlorophyll-containing plastid as found within host cells with thylakoids organized into grana and frets, or stroma thylakoids, and embedded in a stroma. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host cell chloroplast thylakoid membrane

Any sac-like membranous structures (cisternae) in a chloroplast found in host cells, combined into stacks (grana) and present singly in the stroma (stroma thylakoids or frets) as interconnections between grana. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host cell chloroplast part

Any constituent part of a chloroplast as it is found in host cells and which are a chlorophyll-containing plastid with thylakoids organized into grana and frets, or stroma thylakoids, and embedded in a stroma. The host is defined as the larger of the organisms involved in a symbiotic interaction.


neuromuscular junction

The junction between the axon of a motor neuron and a muscle fiber. In response to the arrival of action potentials, the presynaptic button releases molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane of the muscle fiber, leading to a change in post-synaptic potential.


excitatory neuromuscular junction of somatic myotube

A neuromuscular junction that functions in the excitation of somatic muscle myotubes, such as an arthropod somatic muscle cells.


inhibitory neuromuscular junction

The junction between the axon of a motor neuron and a muscle fiber. In response to the arrival of action potentials, the presynaptic button releases molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane of the muscle fiber, leading to a change in post-synaptic potential that inhibits muscle contraction.


inhibitory neuromuscular junction of somatic myotube

A neuromuscular junction that functions in the inhibition of somatic muscle myotube contraction. Examples of somatic muscle myotubes include the somatic muscle cells of arthropods.


neuromuscular junction of myotube

A neuromuscular junction in which the target muscle cell is a myotube.


neuromuscular junction of somatic muscle

A neuromuscular junction in which the target muscle cell is a somatic muscle cell, such as those found in nematodes and arthropods.


neuromuscular junction of somatic muscle myotube

A neuromuscular junction in which the target muscle cell is a somatic muscle myotube, such as an arthropod somatic muscle cell.


excitatory neuromuscular junction

The junction between the axon of a motor neuron and a muscle fiber. In response to the arrival of action potentials, the presynaptic button releases molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane of the muscle fiber, leading to a post-synaptic potential responsible for muscle contraction.


smooth endoplasmic reticulum membrane

The lipid bilayer surrounding the smooth endoplasmic reticulum.


excitatory synapse

A synapse in which an action potential in the presynaptic cell increases the probability of an action potential occurring in the postsynaptic cell.


parallel fiber to Purkinje cell synapse

An excitatory synapse formed by the parallel fibers of granule cells synapsing onto the dendrites of Purkinje cells.


cerebellar climbing fiber to Purkinje cell synapse

A synapse of a climbing fiber onto the dendrites of a Purkinje cell in cerebellum. The climbing fiber originates from the inferior olivary nucleus of the medulla oblongata.


asymmetric, glutamatergic, excitatory synapse

A neuron to neuron synapse with a postsynaptic density, that uses glutamate as a neurotransmitter and whose activity results in excitatory postsynaptic potentials.


P1 peroxisome

A subform of peroxisome that corresponds to an intermediate in a peroxisome assembly pathway, which operates by conversion of peroxisomal subforms in the direction P1, P2 -> P3 -> P4 -> P5 -> P6. P1 peroxisomes are distinguished from the other subforms on the bases of buoyant density and protein content; they contain fewer peroxisomal proteins than the other subforms.


rhoptry membrane

The lipid bilayer surrounding a rhoptry.


lytic vacuole membrane

The lipid bilayer surrounding a lytic vacuole and separating its contents from the cytoplasm of the cell.


lysosomal membrane

The lipid bilayer surrounding the lysosome and separating its contents from the cell cytoplasm.


cytolytic granule membrane

The lipid bilayer surrounding the cytolytic granule.


fungal-type vacuole membrane

The lipid bilayer surrounding a vacuole, the shape of which correlates with cell cycle phase. The membrane separates its contents from the cytoplasm of the cell. An example of this structure is found in Saccharomyces cerevisiae.


autolysosome membrane

A lipid bilayer that surrounds an autolysosome, a single-membrane-bounded vesicle in which endogenous cellular material is degraded.


bacterial-type flagellum basal body, distal rod

The portion of the central rod of the bacterial-type flagellar basal body that is distal to the cell membrane; spans most of the distance between the inner and outer membranes.


outer endospore membrane

The outer membrane around a bacterial endospore, located between the endospore cortex and endospore coat.


chloroplast outer membrane

The outer, i.e. cytoplasm-facing, lipid bilayer of the chloroplast envelope.


cell outer membrane

A lipid bilayer that forms the outermost membrane of the cell envelope; enriched in polysaccharide and protein; the outer leaflet of the membrane contains specific lipopolysaccharide structures.


mycolate outer membrane

A mycolic acid-rich cell outer membrane containing a lipid bilayer and long-chain mycolic acids (hydroxylated branched-chain fatty acids) that are covalently linked to the cell wall peptidoglycan via an arabinogalactan network. Found in mycobacteria and related genera (e.g. corynebacteria).


organelle outer membrane

The outer, i.e. cytoplasm-facing in a cellular organelle, lipid bilayer of an organelle envelope.


plastid outer membrane

The outer, i.e. cytoplasm-facing, lipid bilayer of the plastid envelope.


nucleolus

A small, dense body one or more of which are present in the nucleus of eukaryotic cells. It is rich in RNA and protein, is not bounded by a limiting membrane, and is not seen during mitosis. Its prime function is the transcription of the nucleolar DNA into 45S ribosomal-precursor RNA, the processing of this RNA into 5.8S, 18S, and 28S components of ribosomal RNA, and the association of these components with 5S RNA and proteins synthesized outside the nucleolus. This association results in the formation of ribonucleoprotein precursors; these pass into the cytoplasm and mature into the 40S and 60S subunits of the ribosome.


lysosomal matrix

A matrix composed of supramolecular assemblies of lysosomal enzymes and lipids which forms at a pH of 5.0 within the lysosome.


intermediate layer of mitotic spindle pole body

Structure between the central and outer plaques of the mitotic spindle pole body.


lateral element

A proteinaceous core found between sister chromatids during meiotic prophase.


mitochondrial cloud

A prominent mass in the cytoplasm of previtellogenic oocytes. The cloud contains both mitochondria and electron-dense granulofibrillar material (GFM) and is the source of germinal granule material.


Bunina body

Small granular inclusions (about 1-3 microns in diameter) found in the anterior horn cells, and appearing either singly or in a group. Sometimes they are arranged in small beaded chains. Bunina bodies express cystatin C and consist of electron-dense amorphous material that contains tubules or vesicular structures. The amorphous material frequently includes a cytoplasmic island containing neurofilaments and other micro-organelles.


other organism part

Any constituent part of a secondary organism with which the first organism is interacting.


other organism cell membrane

The cell membrane of a secondary organism with which the first organism is interacting.


symbiont cell surface

The cell surface of a secondary, endosymbiont organism with which the first organism is interacting. The symbiont is defined as the smaller of the organisms involved in a symbiotic interaction.


trichocyst

A crystalline exocytotic organelle composed of small, acidic proteins existing primarily as disulphide-linked dimers. The trichocyst is an organelle that releases long filamentous proteins that capture predators in net-like structures, to slow them down when the cell is disturbed. The protein is nontoxic and shaped like a long, striated, fibrous shaft.


postsynaptic cytosol

The region of the cytosol consisting of all cytosol that is part of the postsynapse.


cytosolic region

Any (proper) part of the cytosol of a single cell of sufficient size to still be considered cytosol.


presynaptic cytosol

The region of the cytosol consisting of all cytosol that is part of the presynapse.


unicellular trichome tip

A cell projection part that is the apical most portion of a unicellular trichome apex.


2-micrometer circle DNA

A plasmid commonly found in Saccharomyces, inherited in a non-Mendelian manner and often present in 100-400 copies.


Lewy body corona

The periphery of a Lewy body. In Parkinson's disease, it contains spherical accumulations of filaments arranged in a loose, radiating array.


cleavage furrow rim

The part of the cleavage furrow closest to the cell surface.


right caudal basal body

Any ciliary basal body that is part of a right caudal flagellum found in Giardia species (trophozoite stage).


Golgi cis cisterna

The Golgi cisterna closest to the endoplasmic reticulum; the first processing compartment through which proteins pass after export from the ER.


transmembrane actin-associated (TAN) line

A linear array of nuclear envelope membrane proteins composed of nesprin-2G and SUN2, which couple the nucleus to moving actin cables, resulting in rearward nuclear transport (away from the leading edge).


growth cone leading edge

That part of the growth cone which represents the distal part of the structure.


leading edge of axonal growth cone

That part of the axonal growth cone which represents the distal part of the structure.


gerontoplast

A plastid found in senescing, formerly green tissues that is derived from a chloroplast that undergoes an organized developmental program of senescence.


cholinergic synapse

A synapse that uses acetylcholine as a neurotransmitter.


protein storage vacuole membrane

The lipid bilayer surrounding a protein storage vacuole.


polyhydroxyalkanoate granule

An inclusion body located in the cytoplasm of prokaryotes that consists of polyhydroxyalkanoate (PHA) molecules and associated proteins, surrounded by a phospholipid monolayer; the proteins include PHA synthase, PHA depolymerase and 3HB-oligomer hydroxylase, phasins (PhaPs), which are thought to be the major structural proteins of the membrane surrounding the inclusion, and the regulator of phasin expression PhaR.


megasome

Large, cysteine proteinase rich lysosomes, often found in the amastigote (an intracytoplasmic, nonflagellated form of the parasite) stage of Leishmania species belonging to the mexicana complex.


cyanelle inner membrane

The inner, i.e. lumen-facing, lipid bilayer of the cyanelle envelope; also faces the cyanelle stroma.


A multilamellar subcellular structure formed in the cytoplasm of developing neuron, composed of Tmem240 and Emd proteins.


early endosome lumen

The volume enclosed by the membrane of an early endosome.


late recombination nodule

An electron dense structure that is associated with meiotic chromosomes in pachytene during meiosis I.


bacterial-type flagellum basal body, rod

The central portion of the bacterial-type flagellar basal body, which spans the periplasm and threads through the rings.


contractile vacuole complex

A non-membrane-bounded organelle of eukaryotic cells, especially Protozoa, that fills with water from the cytoplasm and then discharges this externally. One of its functions is osmoregulatory.


kinetoplast

A sub-structure within the large single mitochondrion of kinetoplastid parasites and which is closely associated with the flagellar pocket and basal body of the flagellum.


antipodal site

The pole of the kinetoplast associated with kinetoplast DNA replication. The antipodal sites flank the kinetoplast DNA disk and are positioned approximately 180 degrees apart. In Trypanosoma brucei and Crithidia fasciculata, minicircles are attached at antipodal sites and they contain enzymes that catalyse some of the later reactions in minicircle replication.


cortical Lewy body

Cytoplasmic inclusion similar to a classical Lewy body but lacking a halo of protein fibrils.


inclusion body

A discrete intracellular part formed of aggregated molecules such as proteins or other biopolymers.


nucleolar peripheral inclusion body

Inclusion bodies located at the nucleolar periphery where several nuclear factors are reversibly aggregated and sequestered during acute heat stress or starvation.


classical Lewy body

Cytoplasmic inclusion, 5 to 15 micrometers in diameter, with a dense core surrounded by a halo of 10 to 20 nm wide radially oriented alpha-synuclein fibrils.


nematosome

Cytoplasmic, ball-like inclusion resembling a nucleolus and consisting of a convoluted network of electron-opaque strands embedded in a less dense matrix. It measures approximately 0.9 microns and lacks a limiting membrane. Its strands (diameter = 400-600 A) appear to be made of an entanglement of tightly packed filaments and particles approximately 25-50 A thick. Cytochemical studies suggest the presence of nonhistone proteins and some RNA. Usually only one such structure is present in a cell, and it appears to occur in most ganglion cells. Although they can be seen anywhere in the cell body, nematosomes are typically located in the perinuclear cytoplasm, where they are often associated with smooth-surfaced and coated vesicles.


skein-like inclusion

Intracytoplasmic filamentous structure frequently encountered in preparations immunostained for ubiquitin.


aggresome

An inclusion body formed by dynein-dependent retrograde transport of an aggregated protein on microtubules.


fibrillary inclusion

Cellular inclusion consisting of circular areas filled with fine slender filaments about 10 nanometers in diameter, delimited by a wall of varying complexity (either a single continuous membrane or a tubular network consisting of a fine filamentous material giving the wall a honeycomb appearance). Fibrillary inclusions are found in the cytoplasm of giant cells of Dieters in the lateral vestibular nucleus of the rat; similar structures have been described in the ventral cochlear nucleus, spinal cord, and substantia nigra.


neurofibrillary tangle

Intracellular mass of paired, helically wound protein filaments (also called PHF) lying in the cytoplasm of neuronal cell bodies and neuritic cell processes. Neurofibrillary tangles contain an abnormally phosphorylated form of a microtubule-associated protein, tau. The shape of these inclusions may resemble a flame or a star.


nuclear inclusion body

An intranuclear focus at which aggregated proteins have been sequestered.


glial cytoplasmic inclusion

Non-membrane-bound cytoplasmic inclusions composed of 10-40 nm granule-coated fibrils. These inclusions have an abnormal accumulation of alpha-synuclein protein and are found in association with multiple system atrophy.


Lewy body

Cytoplasmic, spherical inclusion commonly found in damaged neurons, and composed of abnormally phosphorylated, neurofilament proteins aggregated with ubiquitin and alpha-synuclein.


complex laminated body

A cytoplasmic inclusion body found in some lateral geniculate neurons and composed of sheets of tubules (25 nm in diameter) separated by dense material (about 75 nm wide), which together with the tubules whorl give a structure resembling a fingerprint.


laminated body

Inclusion body characterized by regularly spaced sheets of tubules arranged in a whorl pattern resembling a fingerprint. Laminated bodies have been observed in neurons of the lateral geniculate nucleus.


Pick body

Cellular inclusion composed of numerous tau fibrils arranged in a disorderly array. Tau protein is a major component, though Pick bodies also contain ubiquitin, alpha-synuclein, and apolipoprotein E.


hyaline inclusion

A glass-like, pale intracellular inclusion.


fibrillar center

A structure found most metazoan nucleoli, but not usually found in lower eukaryotes; surrounded by the dense fibrillar component; the zone of transcription from multiple copies of the pre-rRNA genes is in the border region between these two structures.


cnida

A giant secretory organelle that comprises a bulb-shape capsule containing a coiled hollow tubule structure attached to it. A cnida defines the phylum Cnidaria.


glutamatergic postsynaptic density

The post-synaptic specialization of a glutamatergic excitatory synapse.


presynaptic active zone membrane

The membrane portion of the presynaptic active zone; it is the site where docking and fusion of synaptic vesicles occurs for the release of neurotransmitters.


central plaque of mitotic spindle pole body

One of three laminate structures that form the mitotic spindle pole body; the inner plaque is on the nuclear face of the spindle pole body.


central plaque of spindle pole body

One of three laminate structures that form the spindle pole body; the central plaque is embedded in the nuclear envelope.


central region of growth cone

The center of the migrating motile tip of a growing nerve cell axon or dendrite.


cellular bud neck contractile ring

A contractile ring, i.e. a cytoskeletal structure composed of actin filaments and myosin, that forms beneath the plasma membrane at the mother-bud neck in mitotic cells that divide by budding in preparation for completing cytokinesis. An example of this structure is found in Saccharomyces cerevisiae.


extrahaustorial matrix

The space between the symbiont plasma membrane and the extrahaustorial membrane of the host.


glyoxysomal membrane

The lipid bilayer surrounding a glyoxysome.


peroxisomal membrane

The lipid bilayer surrounding a peroxisome.


glycosome membrane

The lipid bilayer surrounding a glycosome.


nucleus lagging edge

The area of a motile nucleus furthest from the direction of movement.


bleb

A cell extension caused by localized decoupling of the cytoskeleton from the plasma membrane and characterized by rapid formation, rounded shape, and scarcity of organelles within the protrusion. Blebs are formed during apoptosis and other cellular processes, including cell locomotion, cell division, and as a result of physical or chemical stresses.


mannosome

A specialised tubular organelle, assembled in hexagonal bundles within an external membrane. Mannosomes are specific to molluscs and are thought to be involved in a general stress reaction.


trans-Golgi network membrane

The lipid bilayer surrounding any of the compartments that make up the trans-Golgi network.


ribbon synapse

Type of synapse characterized by an electron-dense ribbon, lamella (bar) or spherical body in the presynaptic process cytoplasm.


photoreceptor ribbon synapse

A ribbon synapse between a retinal photoreceptor cell (rod or cone) and a retinal bipolar cell. These contain a plate-like synaptic ribbon.


cochlear hair cell ribbon synapse

A ribbon synpase of an auditory hair cell of the cochlear. These ribbon synapses contain spherical synaptic ribbons and lack and arciform density.


extrinsic component of postsynaptic membrane

The component of the postsynaptic membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of plasma membrane

The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of presynaptic membrane

The component of the presynaptic membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of presynaptic endocytic zone membrane

The component of the presynaptic endocytic zone membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of postsynaptic specialization membrane

The component of the postsynaptic specialization membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of postsynaptic density membrane

The component of the postsynaptic density membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of external side of plasma membrane

The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to its external surface, but not integrated into the hydrophobic region.


extrinsic component of presynaptic active zone membrane

The component of the presynaptic active zone membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of synaptic membrane

The component of the synaptic membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


extrinsic component of postsynaptic endocytic zone

The component of the postsynaptic endocytic zone membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


bacterial microcompartment

An organelle found in bacteria consisting of a proteinaceous coat containing metabolic enzymes whose purpose is the sequestration or concentration of metabolites and which has the appearance of a polygonal granule by electron microscopy.


perinucleolar chromocenter

A chromocenter adjacent to the nucleolus.


condensed nuclear chromosome

A highly compacted molecule of DNA and associated proteins resulting in a cytologically distinct nuclear chromosome.


meiotic spindle

A spindle that forms as part of meiosis. Several proteins, such as budding yeast Spo21p, fission yeast Spo2 and Spo13, and C. elegans mei-1, localize specifically to the meiotic spindle and are absent from the mitotic spindle.


mitochondrial nucleoid

The region of a mitochondrion to which the DNA is confined.


protein aggregate center

Reversible aggregate of misfolded proteins and chaperones formed to shield thermosensitive proteins from degradation until conditions allow disaggregation and refolding.


crystalloid

A transient, cytoplasmic organelle found in Plasmodium species that resembles a cytoplasmic inclusion body and whose function is poorly understood. Crystalloids form in ookinetes and disappear after ookinete-to-oocyst transformation.


arciform density

An electron dense structure that anchors a synaptic ribbon to the presynaptic membrane.


monolayer-surrounded lipid storage body

A subcellular organelle of plant cells surrounded by 'half-unit' or a monolayer membrane instead of the more usual bilayer. The storage body has a droplet of triglyceride surrounded by a monolayer of phospholipids, interacting with the triglycerides and the hydrophilic head groups facing the cytosol, and containing major protein components called oleosins.


mitochondrial chromosome

A chromosome found in the mitochondrion of a eukaryotic cell.


Z chromosome

The sex chromosome present in both sexes of species in which the female is the heterogametic sex. Two copies of the Z chromosome are present in each somatic cell of males and one copy is present in females.


spectrosome

A germline specific spherical organelle, rich in membrane skeletal proteins. Precursor to the fusome.


spindle

The array of microtubules and associated molecules that forms between opposite poles of a eukaryotic cell during mitosis or meiosis and serves to move the duplicated chromosomes apart.


sex chromosome

A chromosome involved in sex determination.


ascus lipid droplet

Any particle of coalesced lipids in an ascus or ascospore. May include associated proteins.


chloroplast nucleoid

The region of a chloroplast to which the DNA is confined.


chloroplast stromal thylakoid

Unstacked thylakoids that connect the grana stacks through the stroma.


pyrenoid

A non-membrane-bounded organelle found within the chloroplasts of algae and hornworts; responsible for carbon dioxide fixation.


carboxysome

An organelle consisting of a proteinaceous coat and enzymes for the fixation of CO2. It augments the concentration of CO2 in the vicinity of RuBisCO to increase the efficiency of CO2 fixation under atmospheric conditions.


bacterial nucleoid

The region of a bacterial cell to which the DNA is confined.


goblet cell theca

A cup shaped specialization of the cytoskeleton that forms a thin layer located just below the apical mass of mature mucin secretory granules in the cytoplasm of goblet cells of the intestinal epithelium. It consists of an orderly network of intermediate filaments and microtubules. Microtubules are arranged vertically, like barrel staves, along the inner aspect of the theta. Intermediate filaments form two networks: an inner, basketlike network and an outer series of circumferential bundles resembling the hoops of a barrel.


synaptic ribbon

A non-membrane bound, electron dense structure associated that extends perpendicular to the presynaptic membrane in ribbon synapses. The ribbon's surface is studded with small particles to which synaptic vesicles tether via fine filaments. The tethered vesicles function as a pool, several fold greater than the docked pool available for fast release, which supports sustained release of vesicles. Synaptic ribbons may be plate like or spherical.


proplastid nucleoid

The region of a proplastid to which the DNA is confined.


Y chromosome

The sex chromosome present in males of species in which the male is the heterogametic sex; generally, the sex chromosome that pairs with the X chromosome in the heterogametic sex. The Y chromosome is absent from the cells of females and present in one copy in the somatic cells of males.


chloroplast thylakoid

Sac-like membranous structures (cisternae) in a chloroplast combined into stacks (grana) and present singly in the stroma (stroma thylakoids or frets) as interconnections between grana. An example of this component is found in Arabidopsis thaliana.


active sex chromosome

A sex chromosome that has not been inactivated.


polytene chromosome chromocenter

A region at which the centric regions of polytene chromosomes are joined together.


cyanelle thylakoid

A thylakoid found in a cyanelle, which is a type of plastid found in certain algae. The cyanelle contains a photosynthetic membrane resembling that of cyanobacteria.


prothylakoid

Underdeveloped thylakoids found in etioplasts, lacking competent photosynthetic membranes. Rapidly develop into mature thylakoids in the presence of light.


bacterial thylakoid

A thylakoid that is derived from and attached to, but not necessarily continuous with, the plasma membrane, and is not enclosed in a plastid. It bears the photosynthetic pigments in photosynthetic cyanobacteria.


gas vesicle

An intracellular non-membrane-bounded organelle; a hollow structure made of protein, which usually has the form of a cylindrical tube closed by conical end caps. By regulating their relative gas vesicle content, aquatic microbes are able to perform vertical migrations.


nucleolus-like body

A nuclear compartment containing significant amounts of non-nucleolar, spliceosomal components. It is commonly found in germinal vesicle (GV) stage oocytes, and is similar to both nucleoli and sphere organelles.


dynein axonemal particle

An aggregation of axonemal dyneins, their specific assembly factors, and broadly-acting chaperones that is located in the cytoplasm.


autosome

Any chromosome other than a sex chromosome.


thylakoid

A membranous cellular structure that bears the photosynthetic pigments in plants, algae, and cyanobacteria. In cyanobacteria thylakoids are of various shapes and are attached to, or continuous with, the plasma membrane. In eukaryotes they are flattened, membrane-bounded disk-like structures located in the chloroplasts; in the chloroplasts of higher plants the thylakoids form dense stacks called grana. Isolated thylakoid preparations can carry out photosynthetic electron transport and the associated phosphorylation.


organellar chromatophore thylakoid

A thylakoid located in an organellar chromatophore.


plastid thylakoid

Any thylakoid within a plastid.


plastid nucleoid

The region of a plastid to which the DNA is confined.


centriole

A cellular organelle, found close to the nucleus in many eukaryotic cells, consisting of a small cylinder with microtubular walls, 300-500 nm long and 150-250 nm in diameter. It contains nine short, parallel, peripheral microtubular fibrils, each fibril consisting of one complete microtubule fused to two incomplete microtubules. Cells usually have two centrioles, lying at right angles to each other. At division, each pair of centrioles generates another pair and the twin pairs form the pole of the mitotic spindle.


propanediol degradation polyhedral organelle

An organelle found in bacteria consisting of a proteinaceous coat containing enzymes for the degradation of 1,2-propanediol whose purpose is the protection of the rest of the cell from the toxic propionaldehyde product of the enzyme diol dehydratase.


chlorosome

A large enclosure of aggregated pigment, typically bacteriochlorophyll c (BChl c), that acts as a light-harvesting antenna structure and is characteristic of green photosynthetic bacteria (e.g. Chlorobiaceae). The BChl aggregates are organized into lamellar elements by pigment-pigment rather than pigment-protein interactions. Chlorosomes also contain BChl a, carotenoids, quinones, lipids, and proteins, and are attached to the cytoplasmic membrane via a BChl a-containing protein baseplate.


mitotic spindle

A spindle that forms as part of mitosis. Mitotic and meiotic spindles contain distinctive complements of proteins associated with microtubules.


nuclear chromosome

A chromosome that encodes the nuclear genome and is found in the nucleus of a eukaryotic cell during the cell cycle phases when the nucleus is intact.


ventral disc

Specialized organelle found in Giardia species (trophozoite stage) and characterized by a spiral array of microtubules and microtubule-associated structures including dorsal microribbons and crossbridges. The edge of the ventral disc narrows into a lateral crest. The ventral disk mediates mechanical attachment of the trophozoite to the host's intestinal wall, and contains the contractile proteins actinin, alpha-actinin, myosin, and tropomyosin working towards contraction of the disk involved in adherence.


nematocyst

An organelle found in cnidoblast (nematoblast) cells. When matured, these stinging organelles store toxins and can deliver them when the cnidocil (a short extension of the cnidocyst) is stimulated by a prey or another stimulus.


W chromosome

The sex chromosome present in females of species in which the female is the heterogametic sex; generally, the sex chromosome that pairs with the Z chromosome in the heterogametic sex. The W chromosome is absent from the cells of males and present in one copy in the somatic cells of females.


inactive sex chromosome

A sex chromosome that has been inactivated.


X chromosome

The sex chromosome present in both sexes of species in which the male is the heterogametic sex. Two copies of the X chromosome are present in each somatic cell of females and one copy is present in males.


blepharoplast

An intracellular non-membrane-bounded organelle found in multi-ciliated sperm cells of some primitive land plants, and consisting of many radially arranged ninefold symmetric cylinders. The blepharoplast is involved in de novo formation of multiple centrioles; it enlarges and then disintegrates into many procentrioles, which elongate and ultimately nucleate cilia on the surface of the sperm cell.


polytene chromosome

A type of chromosome in a polyploid cell, formed when multiple copies of homologous chromosomes are aligned side by side to give a giant chromosome in which distinct chromosome bands are readily visible.


condensed chromosome

A highly compacted molecule of DNA and associated proteins resulting in a cytologically distinct structure.


granal stacked thylakoid

Appressed thylakoid membranes that are part of a granum (stacked regions). A characteristic of these appressed regions is the preferential localization of photosystem II.


chromocenter

A region in which centric, heterochromatic portions from more than one chromosomes form a compact structure.


podosome

An actin-rich adhesion structure characterized by formation upon cell substrate contact and localization at the substrate-attached part of the cell, contain an F-actin-rich core surrounded by a ring structure containing proteins such as vinculin and talin, and have a diameter of 0.5 mm.


proteasome storage granule

An aggregation of proteasome core protease (CP) and regulatory particle (RP) complexes that localizes in the cytoplasm as dot-like structures when cells are in a quiescent state.


elaioplast

A leucoplast in which oil is stored.


histone locus body

A nuclear body associated with the histone gene locus that is thought to contain all of the factors necessary for histone mRNA transcription and pre-mRNA processing. In Drosophila, U7 snRNP is located in the histone locus body rather than the distinct Cajal body.


mitotic nuclear bridge

A narrow constricted region of the nucleus that forms around the anaphase spindle during closed mitosis, and connects the main portions of the newly forming daughter nuclei.


autophagosome membrane

The lipid bilayer surrounding an autophagosome, a double-membrane-bounded vesicle in which endogenous cellular material is sequestered.


amphisome membrane

Any membrane that is part of an amphisome.


extrinsic component of external side of mycolate outer membrane

The component of mycolate membrane consisting of gene products and protein complexes that are loosely bound to its external surface, but not integrated into the hydrophobic region.


extrinsic component of mycolate outer membrane

The component of mycolate outer membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.


alae of collagen and cuticulin-based cuticle extracellular matrix

Raised, thickened cuticular ridges that run longitudinally, and in parallel, along the left and right sides of the animal. The alae lie above the hypodermal cells known as the lateral seam cells. In C. elegans, alae are produced in L1 larvae, dauer larvae and adult stage animals, where they consist of three, five, and three ridges of distinct morphology, respectively.


host cell late endosome

A prelysosomal endocytic organelle differentiated from host early endosomes by lower lumenal pH and different protein composition. Host late endosomes are more spherical than early endosomes and are mostly juxtanuclear, being concentrated near the microtubule organizing center.


pnictogen molecular entity

A p-block molecular entity containing any pnictogen.


peptide

Amide derived from two or more amino carboxylic acid molecules (the same or different) by formation of a covalent bond from the carbonyl carbon of one to the nitrogen atom of another with formal loss of water. The term is usually applied to structures formed from alpha-amino acids, but it includes those derived from any amino carboxylic acid. X = OH, OR, NH2, NHR, etc.


primary amide

A derivative of an oxoacid RkE(=O)l(OH)m (l =/= 0) in which an acidic hydroxy group has been replaced by an amino or substituted amino group.


amide

An amide is a derivative of an oxoacid RkE(=O)l(OH)m (l =/= 0) in which an acidic hydroxy group has been replaced by an amino or substituted amino group.


carboxamide

An amide of a carboxylic acid, having the structure RC(=O)NR2. The term is used as a suffix in systematic name formation to denote the -C(=O)NH2 group including its carbon atom.


organonitrogen compound

Any heteroorganic entity containing at least one carbon-nitrogen bond.


organic amino compound

A compound formally derived from ammonia by replacing one, two or three hydrogen atoms by organyl groups.


polar tube

A highly specialized structure unique to microsporidia that is required for host cell invasion. In the spore, the polar tube is connected at the anterior end, and then coils around the sporoplasm. Upon appropriate environmental stimulation, the polar tube rapidly discharges out of the spore, pierces a cell membrane and serves as a conduit for sporoplasm passage into the new host cell.


endospore coat

The layer in a bacterial endospore that lies under the exosporium, and is impermeable to many toxic molecules. The coat may also contain enzymes that are involved in endospore germination.


Yb body

A cytoplasmic part that appears as an electron-dense sphere of around 1.5 micron diameter containing Yb protein found in somatic cells of ovary and testis. There are one to two Yb bodies per cell.


leucoplast stroma

The space enclosed by the double membrane of a leucoplast.


linear element

A proteinaceous scaffold associated with fission yeast chromosomes during meiotic prophase. Linear elements consist of a protein complex, LinE, with four main structural components (Rec10, Rec25, Rec27, and Mug20 in S. pombe) associated with chromatin. The resulting structure is related to but not equivalent to the synaptonemal complex.


amyloplast inner membrane

The inner, i.e. lumen-facing, lipid bilayer of the amyloplast envelope; also faces the amyloplast stroma.


perisynaptic space

The extracellular region immediately adjacent to to a synapse.


megagametophyte egg cell nucleus

The nucleus of a plant egg cell. This nucleus is found at the micropylar end of the embryo.


lignin network

An extracellular matrix part that consists of lignin in the form of a three-dimensional polymeric network. Lignins are complex racemic aromatic heteropolymers derived from a variety of phenylpropane monomers coupled together by an assortment of carbon-carbon and ether linkages. Lignin is crucial for structural integrity of the cell wall and stiffness and strength of the stem. In addition, lignin waterproofs the cell wall, enabling transport of water and solutes through the vascular system, and plays a role in protecting plants against pathogens.


hyphal septin band

A septin band, i.e. a diffuse ring composed of a series of septin bars running parallel to the long axis of the cell, located at the junction between the mother cell and the germ tube (hypha) of a fungal cell growing filamentously.


pilus shaft

The long, slender, mid section of a pilus.


lower tip-link density

An electron-dense plaque at the lower end of a stereocilia tip link that provides the anchor in the stereocilia membrane at the tip of the stereocilium from which the tip link rises.


sieve area

A pit-like area in the cell wall of a sieve element; contains pores lined with callose and occupied by strands of protoplasmic material that interconnect the protoplasts of contiguous sieve elements.


nucleoplasmic side of nuclear pore

The side of the nuclear pore complex (NPC) that faces the nucleoplasm.


autolysosome

A type of secondary lysosome in which a primary lysosome has fused with the outer membrane of an autophagosome. It is involved in the second step of autophagy in which it degrades contents with acidic lysosomal hydrolases.


secondary lysosome

Vacuole formed by the fusion of a lysosome with an organelle (autosome) or with a primary phagosome.


left lateral basal body pair

Set of two basal bodies found in Giardia species (trophozoite stage). It comprises the anterior and ventral basal bodies located to the right of the left nucleus of the trophozoite when viewed dorsally.


host cell centrosome

A structure in a host cell comprised of a core structure (in most organisms, a pair of centrioles) and peripheral material from which a microtubule-based structure, such as a spindle apparatus, is organized. Centrosomes occur close to the nucleus during interphase in many eukaryotic cells, though in animal cells it changes continually during the cell-division cycle.


stereocilia tip link

A stereocilia link that is formed by a fine filament running more or less vertically upward from the tip of each shorter stereocilium to attach at a higher point on its adjacent taller neighbor. Tilting the bundle puts tension on the filaments, which pull on mechanically gated ion channels in the membrane of the stereocilia.


axonemal outer doublet

Part of an axoneme consisting in a doublet microtubule. Nine of these outer doublets form the 9+0 axoneme, while the 9+2 axoneme also contains a central pair. Dynein arms attached to the doublets provide the mechanism of movement of the cilium.


dendritic spine

A small, membranous protrusion from a dendrite that forms a postsynaptic compartment, typically receiving input from a single presynapse. They function as partially isolated biochemical and an electrical compartments. Spine morphology is variable:they can be thin, stubby, mushroom, or branched, with a continuum of intermediate morphologies. They typically terminate in a bulb shape, linked to the dendritic shaft by a restriction. Spine remodeling is though to be involved in synaptic plasticity.


postsynapse

The part of a synapse that is part of the post-synaptic cell.


thorny excrescence

Large complex spine protruding from a dendrite. Each excrescence is formed by a cluster of spine heads.


postsynapse of neuromuscular junction

The postsynapse of a neuromuscular junction. In vertebrate muscles this includes the motor end-plate, consisting of postjunctional folds of the sarcolemma.


dinoflagellate sulcus

A cell surface furrow that occurs on the ventral side of a dinoflagellate cell. It partially houses the longitudinal flagellum. The sulcus intersects with the cingulum on the ventral side of a dinoflagellate cell.


cell surface furrow

A furrow that may be found on the cell surface. Examples include the cingulum and sulcus found in some dinoflagellates.


dinoflagellate cingulum

A cell surface furrow that wraps around a dinoflagellate cell; the transverse flagellum lies in it.


dinoflagellate sulcal notch

A dinoflagellate sulcus that extends all the way to the posterior end of the cell (also known as antapex). The presence of a sulcal notch makes the dinoflagellate hypocone appear bilobed.


dinoflagellate apical groove

A cell surface furrow (or groove) found on a dinoflagellate apex. It typically loops around the apex.


attachment organelle membrane

The lipid bilayer surrounding an attachment organelle. This is a region of the cell membrane facing the environment - in mycoplasma, part of the mycolate outer membrane.


T=219 icosahedral capsid

The protein coat that surrounds the infective nucleic acid in some virus particles where the subunits (capsomeres) are arranged to form an icosahedron with T=219 symmetry. T=219 icosahedral capsid is composed of 12 pentameric and 2180 hexameric capsomeres for a total of 13140 capsid proteins.


microtubule minus-end

The end of a microtubule that does not preferentially grow (polymerize).


microtubule end

Any end of a microtubule. Microtubule ends differ in that the so-called microtubule plus-end is the one that preferentially grows by polymerization, with respect to the minus-end.


post-anaphase array microtubule end

Any microtubule end that is part of a post-anaphase array microtubule.


microtubule plus-end

The growing (plus) end of a microtubule. In vitro, microtubules polymerize more quickly at the plus end than at the minus end. In vivo, microtubule growth occurs only at the plus end, and the plus end switches between periods of growth and shortening, a behavior known as dynamic instability.


mitotic spindle astral microtubule end

Any microtubule end that is part of a mitotic spindle astral microtubule.


cytoplasmic microtubule minus-end

A microtubule minus end that is part of a cytoplasmic microtubule.


plasmodesmatal endoplasmic reticulum

Endoplasmic reticulum found in plasmodesmata, junctions connecting the cytoplasm of adjacent plant cells.


sarcoplasmic reticulum

A fine reticular network of membrane-limited elements that pervades the sarcoplasm of a muscle cell; continuous over large portions of the cell and with the nuclear envelope; that part of the endoplasmic reticulum specialized for calcium release, uptake and storage.


smooth endoplasmic reticulum

The smooth endoplasmic reticulum (smooth ER or SER) has no ribosomes attached to it. The smooth ER is the recipient of the proteins synthesized in the rough ER. Those proteins to be exported are passed to the Golgi complex, the resident proteins are returned to the rough ER and the lysosomal proteins after phosphorylation of their mannose residues are passed to the lysosomes. Glycosylation of the glycoproteins also continues. The smooth ER is the site of synthesis of lipids, including the phospholipids. The membranes of the smooth ER also contain enzymes that catalyze a series of reactions to detoxify both lipid-soluble drugs and harmful products of metabolism. Large quantities of certain compounds such as phenobarbital cause an increase in the amount of the smooth ER.


membrane stack

A configuration of endoplasmic reticulum (ER) found in Purkinje cells in the cerebellum and in axons in the lateral vestibular nucleus, consisting of parallel and interconnecting tubules whose outer surfaces are covered by particles or ringlike structures.


rough endoplasmic reticulum

The rough (or granular) endoplasmic reticulum (ER) has ribosomes adhering to the outer surface; the ribosomes are the site of translation of the mRNA for those proteins which are either to be retained within the cisternae (ER-resident proteins), the proteins of the lysosomes, or the proteins destined for export from the cell. Glycoproteins undergo their initial glycosylation within the cisternae.


interphase microtubule organizing center

A microtubule organizing center found in interphase cells, which organize a longitudinal array of three to five MT bundles from the nuclear envelope during interphase. Each MT bundle is composed of two to seven MTs arranged in an antiparallel configuration, with the dynamic MT plus ends extending toward the cell tips and stable minus ends near the nucleus.


host intracellular part

Any constituent part of the living contents of a host cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host chromosome

A structure composed of a very long molecule of DNA and associated proteins (e.g. histones) that carries hereditary information, occurring within a host cell.


host cell synaptic vesicle

A secretory organelle of a host cell, some 50 nm in diameter, of presynaptic nerve terminals; accumulates in high concentrations of neurotransmitters and secretes these into the synaptic cleft by fusion with the 'active zone' of the presynaptic plasma membrane.


Maurer's cleft

A disk-like structure that appears at the periphery of a red blood cell infected by an apicomplexan parasite, characterized by a translucent lumen and an electron-dense coat of variable thickness; often appears to be tethered to the host cell membrane by fibrous connections with the erythrocyte cytoskeleton.


viral replication complex

Specific locations and structures in the virus infected cell involved in replicating the viral genome.


host cell mitochondrial intermembrane space

The region between the inner and outer lipid bilayers of the host cell mitochondrial envelope.


host cell plastid

Any member of a family of organelles as found in the cytoplasm of host cells, which are membrane-bounded and contain DNA. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host symbiosome

A double-enveloped cell compartment, composed of the endosymbiont with its plasmalemma (as inner envelope) and an outer envelope (the perisymbiontic membrane) derived from the host cell.


host cell synaptic vesicle membrane

The lipid bilayer surrounding a host synaptic vesicle.


host cell endosome lumen

The volume enclosed by the membranes of the host cell endosome.


host thylakoid membrane

The pigmented membrane of any host thylakoid.


host cell nuclear part

Any constituent part of a host cell's nucleus, a membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. The host is the larger of the organisms involved in a symbiotic interaction.


host cell Cajal body

A class of nuclear body in the eukaryotic host cell, first seen after silver staining by Ramon y Cajal in 1903, enriched in small nuclear ribonucleoproteins, and certain general RNA polymerase II transcription factors; ultrastructurally, they appear as a tangle of coiled, electron-dense threads roughly 0.5 micrometers in diameter; involved in aspects of snRNP biogenesis; the protein coilin serves as a marker for Cajal bodies. Some argue that Cajal bodies are the sites for preassembly of transcriptosomes, unitary particles involved in transcription and processing of RNA. The host is the larger of the organisms involved in a symbiotic interaction.


host intracellular organelle

Organized structure of distinctive morphology and function, occurring within the host cell. Includes the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton. Excludes the plasma membrane. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host cell smooth endoplasmic reticulum

The irregular network of unit membranes, visible only by electron microscopy, that occurs in the host cell cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The host smooth ER has no ribosomes adhering to the outer surface.


host cell mitochondrial envelope

The double lipid bilayer enclosing the host cell mitochondrion and separating its contents from the host cell cytoplasm; includes the intermembrane space.


symbiont-containing vacuole

Membrane-bounded vacuole within a host cell in which a symbiont organism resides. The vacuole membrane is derived from both the host and symbiont.


double membrane vesicle viral factory lumen

The volume surrounded by the inner membrane of a double membrane vesicle viral factory.


host cell cytoplasm part

Any constituent part of the host cell cytoplasm, all of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host cell viral nucleoid

The region of a host cell that contains the viral genome.


host thylakoid

A membranous cellular structure within the host cell that bears the photosynthetic pigments in plants, algae, and cyanobacteria. In cyanobacteria thylakoids are of various shapes and are attached to, or continuous with, the host plasma membrane. In eukaryotic host cells they are flattened, membrane-bounded disk-like structures located in the chloroplasts; in the chloroplasts of higher plants the thylakoids form dense stacks called grana. Isolated thylakoid preparations can carry out photosynthetic electron transport and the associated phosphorylation.


T=pseudo3 icosahedral viral capsid

The protein coat that surrounds the infective nucleic acid in some virus particles where the subunits (capsomeres) are arranged to form an icosahedron with pseudo T=3 symmetry. The T=pseudo3 capsid is composed of 12 pentameric and 20 hexameric capsomeres.


T=147 icosahedral capsid

The protein coat that surrounds the infective nucleic acid in some virus particles where the subunits (capsomeres) are arranged to form an icosahedron with T=147 symmetry. T=147 icosahedral capsid is composed of 12 pentameric and 1460 hexameric capsomeres for a total of 8820 capsid proteins.


T=169 icosahedral viral capsid

The protein coat that surrounds the infective nucleic acid in some virus particles where the subunits (capsomeres) are arranged to form an icosahedron with T=169 symmetry. T=169 icosahedral capsid is composed of 12 pentameric and 1680 hexameric capsomeres for a total of 10140 capsid proteins.


postsynaptic specialization membrane

The membrane component of the postsynaptic specialization. This is the region of the postsynaptic membrane in which the population of neurotransmitter receptors involved in synaptic transmission are concentrated.


postsynaptic specialization membrane of symmetric synapse

The membrane component of the postsynaptic specialization of a symmetic synapse. This is the region of the postsynaptic membrane in which the population of neurotransmitter receptors involved in synaptic transmission are concentrated.


postsynaptic density membrane

The membrane component of the postsynaptic density. This is the region of the postsynaptic membrane in which the population of neurotransmitter receptors involved in synaptic transmission are concentrated.


nucleoid

The region of a virus, bacterial cell, mitochondrion or chloroplast to which the nucleic acid is confined.


type Ib terminal bouton

Terminal inflated portion of the axon of a glutamatergic neuron, containing the specialized apparatus necessary for the tonic release neurotransmitters that will induce the contraction of muscle. Type Ib terminal boutons are larger than type Is terminal boutons.


basal distal dendrite

Any dendrite in a dendritic tree that emerges near the basal pole of a neuron (e.g. in bipolar neurons, basal dendrites are either on the same side of the soma as the axon, or project toward the axon), and which is farthest away from the neuronal cell body (the soma).


cell wall-bounded periplasmic space

The region between the plasma membrane and the cell wall in organisms lacking an outer cell membrane such as yeast and Gram positive bacteria. The region is thinner than the equivalent in Gram negative bacteria.


monolayer-surrounded lipid storage body outer lipid monolayer

The single layer of phopholipids surrounding a lipid storage body.


dendritic branch

A dendrite arising from another dendrite.


Golgi apparatus

A membrane-bound cytoplasmic organelle of the endomembrane system that further processes the core oligosaccharides (e.g. N-glycans) added to proteins in the endoplasmic reticulum and packages them into membrane-bound vesicles. The Golgi apparatus operates at the intersection of the secretory, lysosomal, and endocytic pathways.


postsynaptic Golgi apparatus

The network of the Golgi apparatus structures located within the postsynapse.


hyphal tip

The end, or tip, of a fungal hypha, where polarized growth occurs during hyphal elongation.


nucleolar chromatin

The portion of nuclear chromatin associated with the nucleolus; includes the DNA encoding the ribosomal RNA.


nucleolus-associated heterochromatin

Dense particles of heterochromatin, consisting of a loosely twisted strand about 600 Angstrom thick, found associated with the nucleolus.


nucleolus organizer region

A region of a chromosome where nucleoli form during interphase, and where genes encoding the largest rRNA precursor transcript are tandemly arrayed.


dendritic spine neck

Part of the dendritic spine that connects the dendritic shaft to the head of the dendritic spine.


S bouton

Synaptic bouton found in the ventral horn of the spinal cord. S boutons range in diameter from 0.5 to 8 um and contain spherical synaptic vesicles.


outer mucus layer

The outer of two mucus layers secreted by epithelial cells in the colon; the outer mucus layer is loosely packed and can be colonized by bacteria.


omegasome membrane

Any membrane that is part of an omegasome.


smooth endoplasmic reticulum cisterna

A subcompartment of the smooth endoplasmic reticulum consisting of lumenal expansion into a flattened, disc-shaped cavity.


subrhabdomeral cisterna

A membrane-bounded compartment that is found at the base of the rhabdomere and contains stored calcium, InsP3 receptors and smooth endoplasmic reticulum Ca2+-ATPase.


sub-surface cisterna

Specialization of the hypolemmal cisterna consisting of either single profiles or closely apposed stacks of endoplasmic reticulum in which the lumen is obliterated, lying 10-20 nm beneath the plasma membrane.


hypolemmal cisterna

Specialized part of the smooth endoplasmic reticulum that closely underlies the plasma membrane, usually within 60 nm or closer.


pseudopodium membrane

The portion of the plasma membrane surrounding a pseudopodium.


ciliary pocket

Invagination of the plasma membrane from which a cilium (also called flagellum) protrudes.


membrane microdomain

A membrane region with a lipid composition that is distinct from that of the membrane regions that surround it.


caveola neck

A membrane microdomain that forms a necklace around the bulb (crater) of a caveola. Intramembrane particles are concentrated in this region and cytoskeletal components, including actin, are highly enriched in the area underlying it.


eisosome membrane domain/MCC

A plasma membrane part that is composed of a furrow-like plasma membrane domain and associated integral transmembrane proteins.


plasma membrane raft

A membrane raft that is part of the plasma membrane.


caveola

A membrane raft that forms small pit, depression, or invagination that communicates with the outside of a cell and extends inward, indenting the cytoplasm and the cell membrane. Examples include flask-shaped invaginations of the plasma membrane in adipocytes associated with caveolin proteins, and minute pits or incuppings of the cell membrane formed during pinocytosis. Caveolae may be pinched off to form free vesicles within the cytoplasm.


dendritic spine membrane

The portion of the plasma membrane surrounding a dendritic spine.


host peribacteroid membrane

A host-derived membrane that surrounds one or more bacteroids (such as nitrogen-fixing bacteroids within legume root nodule cells).


sculpture element

The third layer of the sexine.


platelet glycocalyx

The carbohydrate rich layer at the outermost periphery of a platelet.


right tetrad

Set of four basal bodies found in Giardia species (trophozoite stage). It comprises the right lateral basal body pair and the right middle basal body pair (i.e. the anterior, ventral, caudal and posteriolateral basal bodies located to the left of the right nucleus of the trophozoite when viewed dorsally).


ventral disc supernumerary microtubule array

A partial left-handed spiral array of microtubules that lies generally dorsal to the main ventral disc microtubule array in Giardia species (trophozoite stage).


axonemal central pair

Part of the axoneme consisting of the inner two microtubule doublets of the 9+2 axoneme occurring in most motile cilia.


endocytic vesicle lumen

The volume enclosed by the membrane of an endocytic vesicle.


phagocytic vesicle lumen

The volume enclosed by the membrane of a phagocytic vesicle.


clathrin-coated endocytic vesicle lumen

The volume enclosed by the membrane of a clathrin-coated endocytic vesicle.


early phagosome lumen

The volume enclosed by the membrane of an eary phagosome.


host apoplast

The apoplast region surrounding a host plant cell. Plants may be described as having two major compartments: the living symplast and the non-living apoplast. The apoplast is external to the plasma membrane and includes cell walls, intercellular spaces and the lumen of dead structures such as xylem vessels. Water and solutes pass freely through it. The host is defined as the larger of the organisms involved in a symbiotic interaction.


organic molecular entity

Any molecular entity that contains carbon.


heteroorganic entity

A heteroorganic entity is an organic molecular entity in which carbon atoms or organic groups are bonded directly to one or more heteroatoms.


organochalcogen compound

An organochalcogen compound is a compound containing at least one carbon-chalcogen bond.


organooxygen compound

An organochalcogen compound containing at least one carbon-oxygen bond.


left ventral basal body

Any ciliary basal body that is part of a left ventral flagellum found in Giardia species (trophozoite stage).


endospore-forming forespore

Portion of the cell formed during the process of bacterial sporulation that will ultimately become the core of the endospore. An endospore is a type of dormant cell that is resistant to adverse conditions.


inner layer of spore wall

Either of the two innermost layers of the spore wall, as described in Saccharomyces.


granum

Distinct stack of lamellae seen within chloroplasts. Grana contain the pigments, electron transfer compounds, and enzymes essential to the light-dependent reactions of photosynthesis.


internode region of axon

An axon part that is located between the nodes of Ranvier and surrounded by compact myelin sheath.


cleavage body

A nuclear body that contains proteins involved in pre-mRNA 3'-end cleavage and polyadenylation, such as DDX1, CSTF2 and CPSFs, as well as the transcription factors TFIIE and TFIIF. Cleavage bodies are localized adjacent to Cajal bodies and are involved in mRNA3'-end processing.


F bouton

Synaptic bouton found in the ventral horn of the spinal cord. F boutons range in diameter from 0.5 to 7 um and contain flattened or pleomorphic synaptic vesicles.


eisosome

A cell part that is composed of the eisosome membrane or MCC domain, a furrow-like plasma membrane sub-domain and associated integral transmembrane proteins, and the proteins (eisosome filaments) that form a scaffolding lattice on the cytoplasmic face. Eisosomes broadly affect overall plasma membrane organization.


Organized structure of distinctive morphology and function, not bounded by a lipid bilayer membrane and occurring outside the cell.


cellulosome

An extracellular multi-enzyme complex containing up to 11 different enzymes aligned on a non-catalytic scaffolding glycoprotein. Functions to hydrolyze cellulose.


T-tubule

Invagination of the plasma membrane of a muscle cell that extends inward from the cell surface around each myofibril. The ends of T-tubules make contact with the sarcoplasmic reticulum membrane.


mating projection base

The region where the mating projection meets the bulk of the cell, in unicellular fungi exposed to mating pheromone.


synaptic cleft

The narrow gap that separates the presynaptic and postsynaptic membranes, into which neurotransmitter is released.


apoplast

The cell membranes and intracellular regions in a plant are connected through plasmodesmata, and plants may be described as having two major compartments: the living symplast and the non-living apoplast. The apoplast is external to the plasma membrane and includes cell walls, intercellular spaces and the lumen of dead structures such as xylem vessels. Water and solutes pass freely through it.


perivitelline space

The space between the membrane of an oocyte and a surrounding membranous structure (zona pellucida or perivitelline membrane).


lysosomal lumen

The volume enclosed within the lysosomal membrane.


endolysosome lumen

The volume enclosed by the membrane of an endolysosome. An endolysosome is a transient hybrid organelle formed by fusion of a late endosome with a lysosome.


cytolytic granule

A specialized secretory lysosome that is present in cells with cytolytic capability such as cytotoxic T lymphocytes and natural killer cells. Cytolytic granules mediate the storage and regulated excretion of lytic molecules for killing of target cells.


porous cell septum

A septum or cross wall which does not entirely span the space between two portions of cell wall and may contain a specialized central pore structure. A porous septum allows the movement of organelles and/or cytoplasm between compartments.


dolipore septum

A septum, or cross-wall, between two portions of a cell or hypha; contains a central pore around which the septum is swollen to form a barrel-shaped structure; pore is covered on each side of the septum by a septal pore cap (parenthosome).


host cell synapse

The junction between a nerve fiber of one host neuron and another host neuron or muscle fiber or glial cell; the site of interneuronal communication.


cellular bud neck septin structure

Any of a series of septin structures that are localized in the bud neck of a budding fungal cell during the cell cycle.


annular furrow extracellular matrix

The extracellular matrix part that is a regularly spaced indentation in the outer cortical layer of the cuticle. The pattern of annular furrows corresponds to sites of invaginations in hypodermal cell membranes that, in turn, correspond to submembranous regions where actin microfilament bundles assemble early in lethargus, the first phase of the molting cycle in which activity and feeding decline.


yolk granule

Discrete structures that partition the water-insoluble portion of the yolk of oocytes and ova, which may or may not be membrane enclosed.


symbiont-containing vacuolar membrane network

Tubular network of extensions from the symbiont-containing vacuole membrane that protrude into the host cytoplasm.


cis-Golgi network membrane

The lipid bilayer surrounding any of the compartments that make up the cis-Golgi network.


pellicle

The structure enclosing certain parasite cells such as certain apicomplexa and Euglenozoa; consists of the cell membrane with its associated infrastructure of microtubules, microfilaments and other organelles.


spine apparatus

A specialization of the endomembrane system found in some classes of dendritic spines consisting of two or more closely apposed lamellae with interspersed electron dense material. The endomembrane component is continuous with the smooth endoplasmic reticulum.


dendritic tuft

The terminal specialization found in some types of dendrites which consists of numerous small terminal branches, giving the dendrite a tufted appearance.


peribacteroid fluid

The soluble material inside the peribacteroid membrane, but outside of the bacteroid, within a bacteroid-containing symbiosome.


spindle matrix

A proteinaceous, nuclear-derived structure that embeds the microtubule spindle apparatus from pole to pole in a microtubule-independent manner during mitosis.


climbing fiber

The axon of inferior olive neuron that projects to the cerebellar cortex, largely via the inferior cerebellar peduncle. They range in diameter from 1-3 um and are myelinated until they enter the granule cell layer. They give off collaterals to the deep cerebellar nuclei. They synapse extensively with the dendrites of Purkinje cells in the molecular layer, where each fiber branches repeatedly to climb along the Purkinje cell dendritic tree. Each Purkinje cell is innervated by only a single climbing fiber.


spine synapse

A type of synapse occurring between an axon and a dendritic spine.


brush border

The dense covering of microvilli on the apical surface of an epithelial cell in tissues such as the intestine, kidney, and choroid plexus; the microvilli aid absorption by increasing the surface area of the cell.


cellular bud scar

Crater-like ring of chitinous scar tissue located on the surface of the mother cell. It is formed after the newly emerged daughter cell separates thereby marking the site of cytokinesis and septation. The number of bud scars that accumulate on the surface of a cell is a useful determinant of replicative age.


exopher

An extracellular vesicle that is approximately four microns in diameter, released by budding out of cells into the extracellular space, and hypothesized to be a mechanism for disposal of unwanted cellular material including protein aggregates and damaged organelles.


female germline ring canal outer rim

An electron opaque backbone of the insect ovarian ring canal that is a part of or adjacent to the plasma membrane. The outer rim is established as the cleavage furrow is arrested, and contains F-actin, anillin, glycoproteins and at least one a protein with a high content of phosphorylated tyrosine residues.


free sarcoplasmic reticulum membrane

The part of the sarcoplasmic reticulum membrane that contains calcium pumps and is devoted to calcium uptake. The free sarcoplasmic reticulum membrane consists of the longitudinal sarcoplasmic reticulum membrane and the non-junctional region of the terminal cisterna membrane.


filiform apparatus

A complex of cell wall invaginations in a synergid cell, similar to those in transfer cells.


endospore core

An intracellular part that represents the innermost portion of an endospore; the endospore core is dehydrated, enriched in dipicolinic acid and divalent cations, and metabolically inactive.


CA3 pyramidal cell dendrite

A dendrite of a hippocampal CA3 pyramidal cell.


phagocytic cup lip

The tip or margin of the progressing circular lamella that engulfs a particle during phagocytosis. When the two lips of the cup fuse it is converted into a phagosome.


chlorosome envelope

The structure, composed of a monolayer of glycolipids with embedded proteins, that encloses the pigments and other contents of the chlorosome.


organelle-enclosing lipid monolayer

A lipid monolayer that surrounds and encloses an organelle.


microneme

A small, elongated secretory organelle that forms part of the apical complex, located along the main axis of an apicomplexan parasite cell within the extreme apical region and at the periphery under the inner membrane complex. Of the specialized secretory compartments identified in apicomplexans, micronemes discharge their contents first, during initial contact of the parasite's apical pole with the host cell surface. Micronemal proteins function during parasite attachment and penetration into the target cell.


mitochondrial crista

Any of the inward folds of the mitochondrial inner membrane. Their number, extent, and shape differ in mitochondria from different tissues and organisms. They appear to be devices for increasing the surface area of the mitochondrial inner membrane, where the enzymes of electron transport and oxidative phosphorylation are found. Their shape can vary with the respiratory state of the mitochondria.


magnetosome

A membrane-bound organelle that envelops particles of magnetic iron minerals in magnetotactic bacteria. Magnetosomes form linear chains that align along the cellular motility axis at midcell and function in bacterial navigation along the Earth's magnetic field. They are formed by invagination of the cell inner membrane; in some species they remain connected to the inner membrane, in others they pinch off to form independent intracellular vesicles.


dinoflagellate epicone

The part of a dinoflagellate cell above the cingulum; also referred to as the anterior portion of a dinoflagellate cell. It is separated from the hypocone by the cingulum.


p-block molecular entity

A main group molecular entity that contains one or more atoms of a p-block element.


chalcogen molecular entity

Any p-block molecular entity containing a chalcogen.


etioplast stroma

The space enclosed by the double membrane of an etioplast but excluding the prothylakoid space. It contains the etioplast DNA.


mating projection

The projection formed by unicellular fungi in response to mating pheromone.


central element

A structural unit of the synaptonemal complex found between the lateral elements.


stereocilium

An actin-based protrusion from the apical surface of auditory and vestibular hair cells and of neuromast cells. These protrusions are supported by a bundle of cross-linked actin filaments (an actin cable), oriented such that the plus (barbed) ends are at the tip of the protrusion, capped by a tip complex which bridges to the plasma. Bundles of stereocilia act as mechanosensory organelles.


ascus epiplasm

Ascus cytoplasm that is not packaged into ascospores.


phragmosome

A flattened membranous vesicle containing cell wall components.


eyespot apparatus

A small pigmented organelle used in single-celled organisms to detect light.


C zone

A region of the A band in which myosin-binding protein C is located and that can be seen by electron microscopy. This is a functional zone that also includes myosin.


Gemini of coiled bodies

Nuclear bodies frequently found near or associated with Cajal bodies (also called coiled bodies or CBs). Gemini of coiled bodies, or 'gems', are similar in size and shape to CBs, and often indistinguishable under the microscope. Unlike CBs, gems do not contain small nuclear ribonucleoproteins (snRNPs); they contain a protein called survivor of motor neurons (SMN) whose function relates to snRNP biogenesis. Gems are believed to assist CBs in snRNP biogenesis, and to play a role in the etiology of spinal muscular atrophy (SMA).


nuclear body

Extra-nucleolar nuclear domains usually visualized by confocal microscopy and fluorescent antibodies to specific proteins.


LYSP100-associated nuclear domain

A nuclear body that is enriched in the lymphoid cell-specific protein LYSp100B; LANDs are globular, electron-dense structures and are morphologically distinct from the annular structures characteristic of PML bodies.


omega speckle

A nucleoplasmic speckle distributed in the interchromatin space of cells in close proximity to chromatin. Omega speckles are distinct from interchromatin granules and contain heterogeneous nuclear RNA-binding proteins (hnRNPs).


paraspeckles

Discrete subnuclear bodies in the interchromatin nucleoplasmic space, often located adjacent to nuclear specks. 10-20 paraspeckles are typically found in human cell nuclei.


nuclear speck

A discrete extra-nucleolar subnuclear domain, 20-50 in number, in which splicing factors are seen to be localized by immunofluorescence microscopy.


nuclear dicing body

A small round nuclear body, measuring 0.2-0.8 microns in diameter that is diffusely distributed throughout the nucleoplasm. Several proteins known to be involved in miRNA processing have been localized to these structures. D-bodies are thought to be involved in primary-miRNA processing and/or storage/assembly of miRNA processing complexes.


interchromatin granule

A class of nuclear body measuring 20-25 nm in diameter and distributed throughout the interchromatin space, linked together by thin fibrils. They are believed to be storage centers for various snRNAs, snRNPs, serine/arginine-rich proteins and RNA polymerase II. A typical mammalian cell contains 25-50 clusters of interchromatin granules. Interchromatin granule clusters do not contain the heterogeneous nuclear RNA-binding proteins (hnRNPs).


sphere organelle

A nuclear body that is found in the germinal vesicles of amphibian oocytes, and consist of three major parts: a remarkably spherical body about 5-10 pm in diameter, smaller spherical or nearly spherical granules on the surface, and inclusions of various sizes that strongly resemble the surface granules. The parts of the sphere organelle have distinct compositions, including splicing snRNAs and proteins.


Cajal body

A class of nuclear body, first seen after silver staining by Ramon y Cajal in 1903, enriched in small nuclear ribonucleoproteins, and certain general RNA polymerase II transcription factors; ultrastructurally, they appear as a tangle of coiled, electron-dense threads roughly 0.5 micrometers in diameter; involved in aspects of snRNP biogenesis; the protein coilin serves as a marker for Cajal bodies. Some argue that Cajal bodies are the sites for preassembly of transcriptosomes, unitary particles involved in transcription and processing of RNA.


pseudopodium

A temporary protrusion or retractile process of a cell, associated with flowing movements of the protoplasm, and serving for locomotion and feeding.


dense fibrillar component

A structure found in the nucleolus, which contains newly synthesized preribosomal RNA (pre-rRNA) and a collection of proteins.


cell body fiber

A neuron projection that is found in unipolar neurons and corresponds to the region between the cell body and the point at which the single projection branches.


chromoplast stroma

The space enclosed by the double membrane of a chromoplast but excluding the photosynthetic material.


apicolateral plasma membrane

The apical end of the lateral plasma membrane of epithelial cells.


Golgi apparatus subcompartment

A compartment that consists of a lumen and an enclosing membrane, and is part of the Golgi apparatus.


Golgi trans cisterna

The Golgi cisterna farthest from the endoplasmic reticulum; the final processing compartment through which proteins pass before exiting the Golgi apparatus; the compartment in which N-linked protein glycosylation is completed.


Golgi cisterna

Any of the thin, flattened membrane-bounded compartments that form the central portion of the Golgi complex.


Golgi stack

The set of thin, flattened membrane-bounded compartments, called cisternae, that form the central portion of the Golgi complex. The stack usually comprises cis, medial, and trans cisternae; the cis- and trans-Golgi networks are not considered part of the stack.


apical proximal dendrite

The dendrite of the dendritic tree, which emerges near the apical pole of a neuron, and which is the closest to the cell body of the neuron (the soma).


germline ring canal

Germline specific intercellular bridge. During cyst formation in insects, ring canals interconnect the cells of the cyst, facilitating the passage of cytoplasmic components between cells.


female germline ring canal

An intercellular bridge that connects the germline cells of a female cyst.


male germline ring canal

An intercellular bridge that connects the germline cells of a male cyst.


mitochondrial envelope

The double lipid bilayer enclosing the mitochondrion and separating its contents from the cell cytoplasm; includes the intermembrane space.


vestibular calyx terminal

The giant, cup-shaped axon terminal of a vestibular afferent neuron, serving as a post-synaptic contact to a type I hair cell.


neuron projection terminus

The specialized, terminal region of a neuron projection such as an axon or a dendrite.


calyx of Held

The terminal specialization of a calyciferous axon which forms large synapses in the mammalian auditory central nervous system.


axon terminus

Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal button is a specialized region of it.


cone cell pedicle

A specialized axon terminus which is produced by retinal cone cells. Pedicles are large, conical, flat end-feet (8-10 micrometers diameter) of the retinal cone axon that lie more or less side by side on the same plane at the outer edge of the outer plexiform layer (OPL).


Herring body

The dilated terminal portions of neurosecretory axons constituting the hypothalamohypophyseal tract, found in close proximity to sinusoidal capillaries in the posterior pituitary. Herring bodies consist of aggregates of membrane-bound neurosecretory vesicles where oxytocin or antidiuretic hormone (ADH) are stored prior to release. Each Herring body also contains ATP and either neurophysin I or neurophysin II which bind to oxytocin and ADH, respectively.


nuclear envelope lumen

The region between the two lipid bilayers of the nuclear envelope; 20-40 nm wide.


P2 peroxisome

A subform of peroxisome that corresponds to an intermediate in a peroxisome assembly pathway, which operates by conversion of peroxisomal subforms in the direction P1, P2 -> P3 -> P4 -> P5 -> P6. P2 peroxisomes are distinguished from the other subforms on the bases of buoyant density and protein content; they are the least dense of the subforms observed.


oral apparatus

Complex basket- or funnel-like structure used by the cell to collect food and channel it to the cytostome; includes specialized sub-structures made up of closely-spaced cilia and underlying basal bodies and fibrillar systems.


uropod membrane

The portion of the plasma membrane surrounding a uropod.


cell trailing edge membrane

The portion of the plasma membrane surrounding the trailing edge of a motile cell.


procentriole

A cellular structure that is the site of a developing centriole, which will become a microtubule organizing center. During the canonical pathway of centriole duplication that occurs during the cell division cycle, procentrioles grow at the proximal ends of both mother and daughter centrioles. In the newly divided cells, the original mother and daughter centrioles become mother centrioles while the procentrioles become the new daughter centrioles. Procentrioles can also arise from de novo pathways that occur in multiciliated cells. In ciliated epithelial cells, numerous procentrioles arise form electron dense material referred to as fibrous granules and deuterosomes. The pathway of procentriole formation in multiciliated protists appears to be similar to that in mammalian multiciliated epithelium. In sperm of primative land plants, multiple procentrioles are formed from a blepharoplast giving rise to multicilated sperm cells.


storage vacuole

A vacuole that functions primarily in the storage of materials, including nutrients, pigments, waste products, and small molecules.


fungal-type vacuole

A vacuole that has both lytic and storage functions. The fungal vacuole is a large, membrane-bounded organelle that functions as a reservoir for the storage of small molecules (including polyphosphate, amino acids, several divalent cations (e.g. calcium), other ions, and other small molecules) as well as being the primary compartment for degradation. It is an acidic compartment, containing an ensemble of acid hydrolases. At least in S. cerevisiae, there are indications that the morphology of the vacuole is variable and correlated with the cell cycle, with logarithmically growing cells having a multilobed, reticulated vacuole, while stationary phase cells contain a single large structure.


reservosome

A large membrane-bound endocytic organelle present only in members of the Schizotrypanum subgenus of the Trypanosoma genus and is defined as the site of storage of endocytosed macromolecules and lysosomal enzymes. It is found at the posterior end of epimastigote forms of Trypanosoma cruzi, but absent in amastigotes and trypomastigotes.


terminal cisterna

The portion of sarcoplasmic reticulum devoted to calcium ion storage and calcium ion release.


stigma papilla

A plant cell papilla that is part of a stigma papilla cell.


apical lamina of hyaline layer

A fibrous network that is part of the hyalin layer extracellular matrix. The apical lamina is thought to be principally composed of the glycoproteins fibropellins. This matrix has been found in echinoderms.


extracellular exosome

A vesicle that is released into the extracellular region by fusion of the limiting endosomal membrane of a multivesicular body with the plasma membrane. Extracellular exosomes, also simply called exosomes, have a diameter of about 40-100 nm.


reservosome membrane

The lipid bilayer surrounding a reservosome.


plasma membrane bounded cell projection

A prolongation or process extending from a cell and that is bounded by plasma membrane, e.g. a cilium, lamellipodium, or axon.


microspike

A dynamic, actin-rich projection extending from the surface of a migrating animal cell.


growth cone lamellipodium

A thin sheetlike process extended by the leading edge of an axonal or dendritic growth cone; contains a dense meshwork of actin filaments.


ruffle

Projection at the leading edge of a crawling cell; the protrusions are supported by a microfilament meshwork.


basal dendrite

A dendrite that emerges near the basal pole of a neuron. In bipolar neurons, basal dendrites are either on the same side of the soma as the axon, or project toward the axon.


C-fiber

The axon of a dorsal root ganglion cell that are responsive to pain and temperature. C-fibers are small in diameter (0.2-1.5 um) and unmyelinated.


distal dendrite

The dendrite of the dendritic tree that is farthest away from the neuronal cell body (the soma).


proximal dendrite

The dendrite of the dendritic tree that is closest to the neuronal cell body (the soma).


dendritic tree

The entire complement of dendrites for a neuron, consisting of each primary dendrite and all its branches.


rod spherule

A specialized neuron projection which is the site of synaptic transmission produced by retinal rod cells. Rod spherules are small round enlargements of the axon (3-5 micrometers diameter) or even extensions of the cell body.


dendrite

A neuron projection that has a short, tapering, morphology. Dendrites receive and integrate signals from other neurons or from sensory stimuli, and conduct nerve impulses towards the axon or the cell body. In most neurons, the impulse is conveyed from dendrites to axon via the cell body, but in some types of unipolar neuron, the impulse does not travel via the cell body.


hippocampal mossy fiber

Axon of dentate gyrus granule cell projecting to hippocampal area CA3, characterized by expansions (mossy fiber expansions) giving the fibers a mossy appearance. These unmyelinated axons were first described by Ramon y Cajal.


axonal spine

A spine that originates from the axon, usually from the initial segment.


giant axon

Extremely large, unmyelinated axon found in invertebrates. Has high conduction speeds and is usually involved in panic or escape responses.


filopodium

Thin, stiff, actin-based protrusion extended by the leading edge of a motile cell such as a crawling fibroblast or amoeba, or an axonal or dendritic growth cone, or a dendritic shaft.


dendritic cell dendrite

A branched cellular projection (or cytoplasmic extension) that is extended from the surface of a dendritic immune cell, and which enables the cell to sample luminal pathogens and increase the surface area for antigen presentation to T cells.


rod telodendria

Rod telodendria are projections that originate from the rod pedicle and form gap junctions with other photoreceptors within the outer plexiform layer of the retina.


growth cone filopodium

A thin, stiff protrusion extended by the leading edge of an axonal or dendritic growth cone.


accessory outer segment

A cilium-like cell projection emanating from the inner segment and running alongside the outer segment of photoreceptors.


cone telodendria

Cone telodendria are projections that originate from the cone pedicle and form gap junctions with other photoreceptors within the outer plexiform layer of the retina.


muscle cell projection

A prolongation or process extending from a muscle cell. A muscle cell is a mature contractile cell, commonly known as a myocyte. This cell has as part of its cytoplasm myofibrils organized in various patterns.