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

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


host cell nucleolus

A small, dense body one or more of which are present in the nucleus of eukaryotic host cells.


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 cell nucleoplasm

That part of a host cell's nuclear content other than the chromosomes or the nucleolus. The host is 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 endoplasmic reticulum lumen

The volume enclosed by the membranes of the host cell endoplasmic reticulum.


host cell synaptic vesicle membrane

The lipid bilayer surrounding a host synaptic vesicle.


host cell nuclear lamina

The fibrous, electron-dense layer lying on the nucleoplasmic side of the inner membrane of a host cell nucleus, composed of lamin filaments.


host cell peroxisome

A small host cell organelle enclosed by a single membrane, and found in most eukaryotic cells. Contains peroxidases and other enzymes involved in a variety of metabolic processes including free radical detoxification, lipid catabolism and biosynthesis, and hydrogen peroxide metabolism.


host cell endosome lumen

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


host cell mitochondrion

A semiautonomous, self replicating organelle as found in host cells that occurs in varying numbers, shapes, and sizes in the cell cytoplasm. The host is defined as the larger of the organisms involved in a symbiotic interaction.


host cell perinuclear region of cytoplasm

The host cell cytoplasm situated near, or occurring around, the host nucleus.


host thylakoid membrane

The pigmented membrane of any host thylakoid.


host cell cytoplasmic vesicle

A vesicle formed of membrane or protein, found in the cytoplasm of a host cell.


host cell lysosome

A small lytic vacuole that has cell cycle-independent morphology and is found in most host animal cells and that contains a variety of hydrolases, most of which have their maximal activities in the pH range 5-6. The contained enzymes display latency if properly isolated. About 40 different lysosomal hydrolases are known and host cell lysosomes have a great variety of morphologies and functions.


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 lipid droplet

Any particle of coalesced lipids in the cytoplasm of a host cell. May include associated proteins.


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.


host cytoskeleton

A cellular structure that forms the internal framework of eukaryotic and prokaryotic host cells. The cytoskeleton includes intermediate filaments, microfilaments, microtubules, the microtrabecular lattice, and other structures characterized by a polymeric filamentous nature and long-range order within the cell. The various elements of the cytoskeleton not only serve in the maintenance of cellular shape but also have roles in other cellular functions, including cellular movement, cell division, endocytosis, and movement of organelles.


host cell cytoplasmic vesicle membrane

The lipid bilayer surrounding a host cell cytoplasmic vesicle.


host cell endosome

A membrane-bounded organelle that carries materials newly ingested by endocytosis. It passes many of the materials to host cell lysosomes for degradation.


host cell nuclear matrix

The dense fibrillar network lying on the inner side of the host nuclear membrane.


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 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 ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached).


host cell cytosol

The part of the host cell cytoplasm that does not contain organelles but which does contain other particulate matter, such as protein complexes.


host cell viral nucleoid

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


host intracellular membrane-bounded organelle

Organized structure of distinctive morphology and function, as found in host cells, bounded by a single or double lipid bilayer membrane and occurring within the cell. Includes the nucleus, mitochondria, plastids, vacuoles, and vesicles. Excludes the plasma membrane. The host is defined as the larger of the organisms involved in a symbiotic interaction.


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.


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.


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.


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.


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.


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 cell surface

The external part of the host cell wall and/or host plasma membrane.


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.


left ventral basal body

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


acellular membrane

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An acellular anatomical structure that is the bounding layer of a anatomical structure.


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.


host cell plasma membrane

The plasma membrane surrounding a host cell.


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.


short microvillus layer

A layer of microvilli covering lymphocytes.


proximal convoluted tubule brush border

A brush border layer that is part of a proximal tubule in the kidney.


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.


host cell mitochondrial membrane

Either of the lipid bilayers that surround the host cell mitochondrion and form the host cell mitochondrial envelope.


host cell mitochondrial inner membrane

The inner, i.e. lumen-facing, lipid bilayer of the host cell mitochondrial envelope. It is highly folded to form cristae.


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.


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.


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).


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 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 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.


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.


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.


calyx of Held

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


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.


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.


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).


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.


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.


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.


cytoneme

A long, thin, polarized cell projection that contains actin and can extend for distances many times the diameter of the cell. Cytonemes represent extensions of cell cytoplasm and typically have a diameter of approximately 0.2um.


pollen tube

A tubular cell projection that is part of a pollen tube cell and extends from a pollen grain.


macropinocytic cup

A cell projection that forms at the site of macropinocytosis, a form of endocytosis that results in the uptake of relatively large amounts of extracellular fluid. The macropinocytic cup membrane selectively excludes certain proteins, such as H36 or PM4C4 in Dictyostelium, and the underlying cytoskeleton is enriched in F-actin and coronin.


primary dendrite

A dendrite emerging from the cell body (the soma) of a neuron.


parallel fiber

A parallel fiber results from the bifurcation of a cerebellar granule cell axon in the molecular layer into two diametrically opposed branches, that are oriented parallel to the long axis of the folium.


neuron spine

A small membranous protrusion, often ending in a bulbous head and attached to the neuron by a narrow stalk or neck.


cerebellar mossy fiber

An axon arising from cerebellar projecting cells in the cochlea, vestibular nuclei, spinal cord, reticular formation, cerebellar nuclei and basilar pontine nuclei. Mossy fibers enter through all three cerebellar peduncles and send collaterals to the deep cerebellar nuclei, then branch in the white matter and terminate in the granule cell layer. Through this branching, a given mossy fiber can innervate several folia. Mossy fibers synapse on granule cells. The synaptic contacts are made at enlargements along the length of the mossy fiber called mossy fiber rosettes. The enlargements of the rosettes give the axons a mossy-looking appearance in Golgi stained preparations.


gemmule

Spine-like process found on some neurons, e.g., periglomerular cells of olfactory cortex.


proximal neuron projection

The portion of an axon or dendrite that is close to the neuronal cell body.


podocyte primary projection

A cell projection originating from a renal glomerular podocyte and extending to the renal glomerular podocyte foot.


rhabdomere microvillus

Thin cylindrical membrane-covered projection on the surface of a rhabdomere.


podocyte foot

A cell projection of a podocyte (glomerular visceral epithelial cell) forming a foot-like structure projecting from a podocyte primary projection, that wraps around capillaries of a renal glomerulus. Adjacent feet (pedicels) interdigitate, leaving thin filtration slits between them, which are covered by slit diaphragms.


uropod

A membrane projection with related cytoskeletal components at the trailing edge of a cell in the process of migrating or being activated, found on the opposite side of the cell from the leading edge or immunological synapse, respectively.


cell hair

A long, thin cell projection that contains F-actin and tubulin, with microtubules centrally located and F-actin peripherally located.


telodendria

Telodendria are projections that originate from the axon pedicle and form gap junctions with other neurons.


apical distal dendrite

Any dendrite in a dendritic tree that emerges near the apical pole of a neuron, and which is farthest away from the neuronal cell body (the soma).


dentate gyrus mossy fiber

Distinctive, unmyelinated axons produced by granule cells.


dendritic filopodium

A small, membranous protrusion found primarily on dendritic stretches of developing neurons. May receive synaptic input, and can develop into dendritic spines.


basal proximal 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 the closest to the cell body of the neuron (the soma).


rhabdomere

The specialized microvilli-containing organelle on the apical surfaces of a photoreceptor cell containing the visual pigment rhodopsin and most of the proteins involved in phototransduction.


dinoflagellate peduncle

A small, flexible, finger-like projection of cytoplasm containing an array of microtubles and located near the flagellar pores in some photosynthetic as well as nonphotosynthetic dinoflagellate species. Its functions are not fully understood, but it has been associated with feeding behavior (phagotrophy).


apical dendrite

A dendrite that emerges near the apical pole of a neuron. In bipolar neurons, apical dendrites are located on the opposite side of the soma from the axon.


plastid

Any member of a family of organelles found in the cytoplasm of plants and some protists, which are membrane-bounded and contain DNA. Plant plastids develop from a common type, the proplastid.


phenyloplast

A chloroplast-derived plastid in which the solid form of phenol is stored.


chloroplast

A chlorophyll-containing plastid with thylakoids organized into grana and frets, or stroma thylakoids, and embedded in a stroma.


apicoplast

The plastid organelle found in apicomplexans.


etioplast

A plastid arrested in the development of chloroplasts from proplastids due to absence of light or low light conditions.


leucoplast

A colorless plastid involved in the synthesis of monoterpenes.


chromoplast

A plastid containing pigments other than chlorophyll, usually yellow and orange carotenoid pigments.


proteinoplast

A leucoplast in which protein is stored.


cyanelle

A plastid that contains unstacked, phycobilisome-bearing thylakoid membranes and is surrounded by a double membrane with a peptidoglycan layer in the intermembrane space between the two envelope membranes. Cyanelles are characteristic of algae in the class Glaucophyta, and may represent an ancestral form of plastid.


cell plate

The nascent cell membrane and cell wall structure that forms between two daughter nuclei near the center of a dividing plant cell. It develops at the equitorial region of the phragmoplast. It grows outwards to join with the lateral walls and form two daughter cells.


myelin sheath

An electrically insulating fatty layer that surrounds the axons of many neurons. It is an outgrowth of glial cells: Schwann cells supply the myelin for peripheral neurons while oligodendrocytes supply it to those of the central nervous system.


egg chorion

A protective, noncellular membrane that surrounds the eggs of various animals including insects and fish.


primary lysosome

A lysosome before it has fused with a vesicle or vacuole.


ascospore-type prospore nucleus

Any nucleus that is part of a ascospore-type prospore.


bacterial-type flagellum filament

The long (approximately 20 nm), thin external structure of the bacterial-type flagellum, which acts as a propeller.


dendritic spine origin

The part of the dendritic spine neck where the spine arises from the dendritic shaft.


archaeal-type flagellum

A non-membrane-bounded organelle superficially similar to a bacterial-type flagellum; they both consist of filaments extending outside the cell, and rotate to propel the cell, but the archaeal flagella (also called archaella) have a unique structure which lacks a central channel. Similar to bacterial type IV pilins, the archaeal flagellins (archaellins) are made with class 3 signal peptides and they are processed by a type IV prepilin peptidase-like enzyme. The archaellins are typically modified by the addition of N-linked glycans which are necessary for proper assembly and/or function.


ventral disc overlap zone

A region of the ventral disc of Giardia species (trophozoite stage) where two portions of the same array of microtubules overlap (the microtubule array makes a complete circle and overlaps on itself).


intercellular bridge

A direct connection between the cytoplasm of two cells that is formed following the completion of cleavage furrow ingression during cell division. They are usually present only briefly prior to completion of cytokinesis. However, in some cases, such as the bridges between germ cells during their development, they become stabilised.


pollen tube tip

The region at growing end of the pollen tube cell, where polarized growth occurs.


microvillus membrane

The portion of the plasma membrane surrounding a microvillus.


extrachromosomal rDNA circle

Circular DNA molecules encoding ribosomal RNA that are replicated independently of chromosomal replication. These molecules originate in the chromosome but are excised and circularized, often by intramolecular homologous recombination between direct tandem repeats.


axonemal basal plate

Part of the axoneme consisting of a highly electron-dense region at the distal end of the ciliary transition zone within the axonemal lumen at which the axonemal central pair of microtubules is connected to the rest of the axonemal structure.


medial membrane band

A sterol-rich region of the plasma membrane which forms at the cell surface overlying the contractile ring and spreads into the invaginating plasma membrane surrounding the septum.


vacuolar lumen

The volume enclosed within the vacuolar membrane.


somatic portion of tanycyte

Portion of a tanycyte that lies within the ependyma and contains the nucleus. A tanycyte is a specialized elongated ventricular ependymal cell that has processes that extend to the outer, or pial, surface of the CNS.


subsynaptic reticulum

An elaborate tubulolamellar membrane system that underlies the postsynaptic cell membrane.


plant cell papilla

A cell projection that is a short, rounded projection from a plant epidermal cell.


tail portion of tanycyte

Elongated process of a tanycyte, devoid of cytoplasmic extensions, that courses through the hypothalamic nuclei to form small endfoot processes that terminate either on blood vessels or at the pial surface of the brain. A tanycyte is a specialized elongated ventricular ependymal cell.


bacterial-type flagellum basal body

One of the three major substructures of the bacterial-type flagellum, the basal body is embedded in the cell envelope (the plasma membrane, peptidoglycan cell wall, and, if one is present, the outer membrane); it houses the secretion apparatus that exports the more distal components and the flagellar motor.


yeast-form cell wall

The wall surrounding a cell of a dimorphic fungus growing in the single-cell budding yeast form, in contrast to the filamentous or hyphal form.


host cell plasmodesma

A fine cytoplasmic channel, found in all higher plants, that connects the cytoplasm of one host cell to that of an adjacent host cell.


manchette

A tubular array of microtubules that extends from the perinuclear ring surrounding the spermatid nucleus to the flagellar axoneme. The manchette may also contain F-actin filaments.


contractile actin filament bundle

An actin filament bundle in which the filaments are loosely packed (approximately 30-60 nm apart) and arranged with opposing polarities; the loose packing allows myosin (usually myosin-II) to enter the bundle.


extrahaustorial membrane

The membrane surrounding the symbiont haustorium during symbiosis, derived from the host plasma membrane.


ectexine

The outer part of the exine, which stains positively with basic fuchsin in optical microscopy and has higher electron density in conventionally prepared TEM sections.


periphagosomal region of cytoplasm

Cytoplasm situated near, or occurring around, a phagosome.


actin body

An amorphous cytoskeletal structure consisting of aggregated actin filaments and associated proteins (including fibrin and capping protein) in which there is little or no actin filament turnover. In yeast (S. pombe and S. cerevisiae) these are found only in quiescent cells and are thought to serve as a reserve store of actin.


karyomere

A membrane-bound intermediate cleavage-stage structure of individual or groups of chromosomes that coalesces and fuses with other karyomeres to form a nucleus during interphase. Karyomere formation occurs in blastomeres undergoing rapid cell division.


actin tubule

A cellular structure, approximately 13 nm in diameter, consisting of three actin filaments bundled together.


megasporocyte nucleus

The nucleus of a megasporocyte, a diploid cell that undergoes meiosis to produce four megaspores, and its descendents.


old cell pole

The cell pole distal from the most recent cell division.


sperm fibrous sheath

A cytoskeletal structure surrounding the axoneme and outer dense fibers of the sperm flagellum. Consists of two longitudinal columns connected by closely arrayed semicircular ribs that assemble from distal to proximal throughout spermiogenesis. The fibrous sheath probably influences the degree of flexibility, plane of flagellar motion, and the shape of the flagellar beat.


pathogen-containing vacuole membrane

Host-derived membrane of a pathogen-containing vacuole.


bacterial-type flagellum hook

The portion of the bacterial-type flagellum that connects the filament to the basal body.


new cell pole

The cell pole proximal to the most recent cell division.


thylakoid lumen

The volume enclosed by a thylakoid membrane.


mitotic actomyosin contractile ring, intermediate layer

The region of the mitotic actomyosin ring in between the proximal layer and the actin filament layer. This region contains the accessory protein network, some actin filaments and connections between the proximal layer and the actin filament layer.


hemicellulose network

Network composed of hemicelluloses; members of a class of plant cell wall polysaccharide that cannot be extracted from the wall by hot water or chelating agents, but can be extracted by aqueous alkali. Includes xylan, glucuronoxylan, arabinoxylan, arabinogalactan II, glucomannan, xyloglucan and galactomannan.


A membrane-bounded flattened sac that is formed during micropexophagy between the membrane tips of an engulfing vacuole, completing the engulfment and sequestration of peroxisomes from the cytosol, and forming a micropexophagic body within the lumen of the vacuole.


generative cell nucleus

The nucleus of the generative cell, a cell contained within the pollen grain that will divide to produce two haploid sperm cells.


P6 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. P6 peroxisomes are distinguished from the other subforms on the bases of buoyant density and protein content, and are equivalent to mature peroxisomes.


microtubule organizing center attachment site

A region of the nuclear envelope to which a microtubule organizing center (MTOC) attaches; protein complexes embedded in the nuclear envelope mediate direct or indirect linkages between the microtubule cytoskeleton and the nuclear envelope.


perinuclear endoplasmic reticulum lumen

The volume enclosed by the membranes of the perinuclear endoplasmic reticulum.


polyadic synapse

A synapse consisting of a single presynapse and multiple postsynapses. These postsynapses may come from the same cell of from different cells. Polyadic synapses are common in arthropod and nematode central nervous systems.


mating projection membrane

The portion of the plasma membrane surrounding a mating projection, the projection formed by unicellular fungi in response to mating pheromone.


methane-oxidizing organelle

A cytoplasmic, membrane-bounded compartment found within Methanotrophic bacteria that contains enzymes and electron transfer proteins for methane catabolism. This structure is analogous to the thylakoid of Cyanobacteria and the anammoxosome of anaerobic ammonium oxidation organisms.


cleavage apparatus septin structure

Any of a series of structures composed of septins and septin-associated proteins localized to the cleavage plane which are involved in cytokinesis.


rod photoreceptor outer segment

The outer segment of a vertebrate rod photoreceptor that contains sealed membrane discs that are not connected to the ciliary membrane and containing rhodopsin photoreceptor proteins.


lytic vacuole within protein storage vacuole

A membrane-bounded compartment containing crystals of phytic acid and proteins characteristic of a lytic vacuole, found within a storage vacuole.


ciliary cap

An intracellular compartmentalized cilium structure found in insect spermatids which is bounded by a membrane derived from the invagination of the cell membrane that remains associated with the primary cilium as it is internalized. The ciliary cap is maintained at the end of the axoneme distal to the centriole and is separated from the cytosolic axoneme/cytoplasm by a putative transition zone, which may extend into the ciliary cap, and include a structure at the base of the ciliary cap termed the ring centriole.


host extracellular space

The space within a host but external to the plasma membrane of host cells, e.g. within host bloodstream.


female germline ring canal inner rim

A proteinaceous actin-rich layer of the insect ovarian ring canal that forms subcortically to the outer rim. The electron dense inner rim accumulates after the final mitotic division of each germline syncytia, and contains actin, a phosphotyrosine protein, and a number of cytoskeletal proteins.


cortical layer of collagen and cuticulin-based cuticle extracellular matrix

The cuticle layer that lies directly beneath the lipid-containing epicuticle. The cortical layer contains collagens and insoluble, non-collagenous cuticulins and is characterized by a distinct annular pattern consisting of regularly spaced annular ridges delineated by annular furrows. An example of this component is found in Caenorhabditis elegans.


ascospore-type prospore

An immature spore undergoing development. The spore usually consists of nucleic acid, prospore membrane(s) that encase the nucleic acid, and ultimately a cell wall that covers the membrane(s). This type of spore is observed in ascospore-forming fungi.


phagocytic cup

An invagination of the cell membrane formed by an actin dependent process during phagocytosis. Following internalization it is converted into a phagosome.


male germ cell nucleus

The nucleus of a male germ cell, a reproductive cell in males.


exosporium

The outermost layer of a bacterial endospore, which is loosely attached and located outside of the endospore coat. It is generally composed of protein, carbohydrate, and perhaps lipid.


mitotic actomyosin contractile ring

A cytoskeletal structure composed of actin filaments, myosin, and myosin-associated proteins that forms beneath the plasma membrane of many cells, including animal cells and yeast cells, in a plane perpendicular to the axis of the mitotic spindle, i.e. the cell division plane. Ring contraction is associated with centripetal growth of the membrane that divides the cytoplasm of the two future daughter cells. In animal cells, the mitotic contractile ring is located inside the plasma membrane at the location of the cleavage furrow. In budding fungal cells, e.g. mitotic S. cerevisiae cells, the mitotic contractile ring forms beneath the plasma membrane at the mother-bud neck before mitosis.


multiple synapse bouton

A single axon terminal bouton making contact onto two or more dendritic spines protruding either from a single dendrite or from multiple dendrites.


cellular bud membrane

The portion of the plasma membrane surrounding a cellular bud.


microbody lumen

The volume enclosed by the membranes of a microbody.


extracellular core region of desmosome

The desmosomal part containing the desmosomal cadherins, desmogleins and desmocollins, that establish contact and adhere to neighboring cells in a Ca2+-dependent manner.


amyloplast starch grain

Plant storage body for amylose and amylopectin, 1-100um in diameter, and located in amyloplasts. Also contains small amounts of enzymes, amino acids, lipids and nucleic acids. The shape of the grain varies widely amongst species, but is often spherical or disk-shaped.


host cell wall

The rigid or semi-rigid envelope lying outside the host cell membrane of plant, fungal, and most prokaryotic cells, maintaining their shape and protecting them from osmotic lysis. In plants it is made of cellulose and, often, lignin; in fungi it is composed largely of polysaccharides; in bacteria it is composed of peptidoglycan.


plastid intermembrane space

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


mating projection tip membrane

The portion of the plasma membrane surrounding a mating projection tip.


rhabdomere microvillus membrane

The portion of the plasma membrane surrounding a microvillus of a rhabdomere.


spore inner membrane

The membrane surrounding the spore core (endospore core) that separates it from its external environment.


cell wall

The rigid or semi-rigid envelope lying outside the cell membrane of plant, fungal, most prokaryotic cells and some protozoan parasites, maintaining their shape and protecting them from osmotic lysis. In plants it is made of cellulose and, often, lignin; in fungi it is composed largely of polysaccharides; in bacteria it is composed of peptidoglycan; in protozoan parasites such as Giardia species, it's made of carbohydrates and proteins.


host cellular component

Any cellular component of a host cell. The host is an organism in which another organism, for instance a parasite or symbiont, spends part or all of its life cycle and from which it obtains nourishment and/or protection.


mitochondrial inner boundary membrane

The portion of the mitochondrial inner membrane that is not invaginated to form cristae. The inner boundary membrane lies parallel to the outer membrane.


macropinocytic cup cytoskeleton

The part of the cortical actin cytoskeleton that forms part of a macropinocytic cup.


bacterial-type flagellum basal body, MS ring

One of the rings of the bacterial-type flagellar basal body; a double-flanged ring that anchors the basal body to the cytoplasmic membrane.


multivesicular body lumen

The volume enclosed by the outermost membrane of a multivesicular body.


pilus

A proteinaceous hair-like appendage on the surface of bacteria ranging from 2-8 nm in diameter.


pairing center

A special chromosome region located towards one end of a chromosome that contains dispersed copies of short, repetitive DNA sequences and functions as a cis-acting element essential for presynaptic homologous chromosome pairing and chromosome-nuclear envelope attachment.


nucleomorph

A small, vestigial nucleus found in some plastids that derive from a eukaryotic endosymbiont. Observed in chlorarachniophytes and cryptomonads, which acquired their plastids from a green and red alga respectively.


Gram-positive-bacterium-type cell wall

A layer of peptidoglycan found outside of the cytoplasmic membrane. The peptidoglycan is relatively thick (20-80nm) and retains the primary stain of the Gram procedure, thus cells appear blue after Gram stain. The cell walls often contain teichoic acids (acidic anionic polysaccharides) bound to the peptidoglycan. Examples of this component are found in Gram-positive bacteria.


microsporocyte nucleus

The nucleus of the microsporocyte. The microsporocyte is a diploid cell in which meiosis will occur, resulting in four microspores. A microspore is a spore that, in vascular plants, gives rise to a male gametophyte.


division septum

A cell septum which forms as part of the division site and functions in the compartmentalization of a cell into two daughter cells at division. A division septum spans a cell and does not allow exchange of organelles or cytoplasm between compartments.


ensheathing process

A cell projection (often from glial cells such as Schwann cells) that surrounds an unmyelinated axon or cell soma.


proximal portion of axoneme

The portion of the axoneme that is close to the base of the cilium.


female germ cell nucleus

The nucleus of the female germ cell, a reproductive cell in females.


bacterial outer membrane vesicle

A spherical, bilayered proteolipid vesicle released from gram-negative bacterial outer membranes.


type I terminal bouton

Terminal inflated portion of the axon of a glutamatergic neuron, containing the specialized apparatus necessary to release neurotransmitters that will induce the contraction of muscle. The axon terminus is considered to be the whole region of thickening and the terminal bouton is a specialized region of it.


fungal-type cell wall

A rigid yet dynamic structure surrounding the plasma membrane that affords protection from stresses and contributes to cell morphogenesis, consisting of extensively cross-linked glycoproteins and carbohydrates. The glycoproteins may be modified with N- or O-linked carbohydrates, or glycosylphosphatidylinositol (GPI) anchors; the polysaccharides are primarily branched glucans, including beta-linked and alpha-linked glucans, and may also include chitin and other carbohydrate polymers, but not cellulose or pectin. Enzymes involved in cell wall biosynthesis are also found in the cell wall. Note that some forms of fungi develop a capsule outside of the cell wall under certain circumstances; this is considered a separate structure.


photoreceptor connecting cilium

The portion of the photoreceptor cell cilium linking the photoreceptor inner and outer segments. It's considered to be equivalent to the ciliary transition zone.


nuclear matrix

The dense fibrillar network lying on the inner side of the nuclear membrane.


multiple synapse bouton, contacting multiple dendrites

A single axon terminal bouton making contact onto two or more dendritic spines protruding from multiple dendrites.


host cell membrane pore complex

Any small opening in a host cell membrane that allows the passage of gases and/or liquids, composed of host proteins.


migrasome

A vesicular organelle that forms on retraction fibers behind migrating cells and mediates the release of cytoplasmic contents during cell migration.


mitotic nuclear bridge midzone

The central region of a mitotic nuclear bridge, distal to the main portions of the daughter nuclei.


pellicular membrane

The portion of the plasma membrane surrounding the pellicle, a structure enclosing some parasite cells such as certain apicomplexa and Euglenozoa. These membranes are associated with an infrastructure of microtubules, microfilaments, and other organelles.


myofilament

Any of the smallest contractile units of a myofibril (striated muscle fiber).


leading edge of lamellipodium

That part of the lamellipodium which represents the distal part of the structure.


polytene chromosome ectopic fiber

A thread-like connection joining two regions of ectopically paired polytene chromosomes.


photoreceptor distal connecting cilium

The distal region of the photoreceptor connecting cilium is structurally unique to the photoreceptor and is maintained by retina-specific protein, SPATA7, and its interacting partners RPGR and RPGRIP1. It is essential for photoreceptor sensory cilium stability.


ficolin-1-rich granule lumen

Any membrane-enclosed lumen that is part of a ficolin-1-rich granule.


tertiary granule lumen

Any membrane-enclosed lumen that is part of a tertiary granule.


right ventral basal body

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


microneme membrane

The lipid bilayer surrounding a microneme.


phragmoplast

The phragmoplast is a plant cell specific cytoplasmic structure composed of cytoskeletal polymers, membranes, and associated cytosolic proteins that functions as the focused secretory module for assembling the cell plate.


new growing cell tip

A cell tip that was newly formed at the last cell division, and that has started to grow after the cell has activated bipolar cell growth (i.e. in which new end take-off, NETO, has taken place). New end take-off is when monopolar cells initiate bipolar growth.


chloroplast inner membrane

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


apical cytoplasm

The region of the cytoplasm located at the apical side of the cell. Used in reference to animal polarized epithelial cells.


ventral surface of cell

The surface of a migrating cell that is in contact with the substratum or cell layer.


glycocalyx

A carbohydrate rich layer at the outermost periphery of a cell.


keratohyalin granule

A cytoplasmic, non-membrane bound granule of, at least, keratinocyte. Associated to keratin intermediate filaments and partially crosslinked to the cell envelope.


micronucleus

A membrane-bounded organelle of ciliated protozoan cells that contains a diploid copy of the cell's complete genome. Sections of contiguous sequence in the macronucleus are often interrupted by internal eliminated sequences (IES), and may be permuted, in micronuclei. Genic transcription is not found in micronuclei. Some ciliate species may contain multiple micronuclei per cell.


bacterial-type flagellum basal body, proximal rod

The portion of the central rod of the bacterial-type flagellar basal body that is proximal to the cell membrane; the proximal rod connects the distal rod to the flagellar motor.


plant-type cell wall

A more or less rigid stucture lying outside the cell membrane of a cell and composed of cellulose and pectin and other organic and inorganic substances.


chrorion micropyle

A single cone-shaped specialization that forms an opening in the egg chorion that allows sperm entry into the egg prior to fertilization.


pirellulosome

A cytoplasmic structure found in bacterial phyla Planctomycetes and Verrucomicrobia containing a condensed nucleoid and ribosomes and surrounded by an intracytoplasmic membrane. It is surrounded by ribosome-free cytoplasm, in a compartment called the paryphoplasm.


dinoflagellate antapex

The anterior most point of a dinoflagellate hypocone.


terminal cisterna lumen

The region between the inner and outer lipid bilayers of the terminal cisterna envelope. This space is enriched in calsequestrin.


stereocilium tip

A distinct compartment at the tip of a stereocilium, distal to the site of attachment to the apical cell surface. It consists of a dense matrix bridging the barbed ends of the stereocilium actin filaments with the overlying plasma membrane, is dynamic compared to the shaft, and is required for stereocilium elongation.


glycosome

A membrane-bounded organelle found in organisms from the order Kinetoplastida that houses the enzymes of glycolysis.


plasmodesmatal cytoplasmic sleeve

The space between the plasma membrane and the desmotubule of a plasmodesma.


concave side of sperm head

The concave part of the late spermatid head or spermatozoon head that forms the ventral portion of the head, particularly in some rodent species.


microsporidian-type endospore

The middle layer in a microsporidian spore wall that lies under the exospore and outside the plasma membrane, containing chitin and proteins.


actin wave

A cellular anatomical entity that is part of the actin cytoskeleton and results in a wave-like propagation of actin networks. It consists of dynamic structures traveling on the ventral (substrate-attached) side of the cell during cell migration, cytokinesis, adhesion and neurogenesis.


epididymosome

A microvesicle of the epididymal fluid, from which spermatozoa aquire membrane proteins.


perinucleolar compartment

The perinucleolar compartment (PNC) is a subnuclear structure associated with, but structurally distinct from, the nucleolus. The PNC contains large amounts of the heterogeneous nuclear ribonucleoprotein complex (hnRNP) called hnRNP 1 (PTB). Many RNA binding proteins as well as RNA polymerase III transcripts are highly enriched in this compartment. PTB and pol III transcripts are required for the integrity of the PNC.


type II terminal bouton

Terminal inflated portion of the axon of a non-glutamatergic neuron, containing the specialized apparatus necessary to release neurotransmitters at a regulatory synapse. The axon terminus is considered to be the whole region of thickening and the terminal bouton is a specialized region of it.


periarbuscular membrane

A host-derived membrane surrounding the symbiont arbuscule during symbiosis.


dinoflagellate apex

The anterior most point of a dinoflagellate epicone.


symbiont-containing vacuole membrane

The lipid bilayer surrounding a symbiont-containing vacuole, derived from both the host and symbiont.


ciliary microtubule quartet

A set of four specialized microtubules that originates from the basal bodies and wraps around the ciliary pocket membrane, likely supporting its distinct flask shape.


symmetric, GABA-ergic, inhibitory synapse

A neuron to neuron synapse that lacks an electron dense postsynaptic specialization, uses GABA as a neurotransmitter and whose activity results in inhibitory postsynaptic potentials.


scintillon

A body present in the cytoplasm of some dinoflagellates, which is the source of bioluminescence; emits light on acidification in the presence of oxygen.


cell pole

Either of two different areas at opposite ends of an axis of a cell.


P3 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. P3 peroxisomes are formed by fusion of P1 and P2 peroxisomes, and are distinguished from the other subforms on the bases of buoyant density and protein content.


surface coat of collagen and cuticulin-based cuticle extracellular matrix

An electron dense, amorphous envelope that comprises the outermost layer of the cuticle. The surface coat is loosely apposed to the epicuticle, has distinct biochemical properties, is synthesized by cells other than the underlying hypodermis, and is labile. In addition to serving as a lubricant to protect against abrasion and dehydration, the surface coat may also play important roles in infection and immune evasion. An example of this component is found in Caenorhabditis elegans.


nuclear envelope adjacent to nuclear pore complex

The region of the nuclear envelope situated in close proximity to a nuclear pore complex.


rod photoreceptor disc lumen

The volume enclosed by the membrane of a rod photoreceptor cell disc membrane.


leaflet of membrane bilayer

Any of the two layers of lipid molecules that constitute a membrane.


distal portion of axoneme

The portion of the axoneme that is close to the tip of the cilium.


sperm mitochondrial sheath

The tightly packed helical sheath of ATP-producing mitochondria restricted to the midpiece of the sperm flagellum.


host cell endomembrane system

A collection of membranous structures involved in transport within the host cell. The main components of the endomembrane system are endoplasmic reticulum, Golgi bodies, vesicles, cell membrane and nuclear envelope. Members of the endomembrane system pass materials through each other or though the use of vesicles. The host is defined as the larger of the organisms involved in a symbiotic interaction.


mucus layer

An extracellular region part that consists of a protective layer of mucus secreted by epithelial cells lining tubular organs of the body such as the colon or secreted into fluids such as saliva. Mucus is a viscous slimy secretion consisting of mucins (i.e. highly glycosylated mucin proteins) and various inorganic salts dissolved in water, with suspended epithelial cells and leukocytes.


extrinsic component of periplasmic side of cell outer membrane

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


nucleus leading edge

The area of a motile nucleus closest to the direction of movement.


dendritic knob

The terminal swelling of an apical dendrite of a ciliated olfactory receptor neuron. Each knob gives rise to 5 to 20 long delicate nonmotile cilia, which extend into the mucus covering the sensory epithelium.


pronucleus

The nucleus of either the ovum or the spermatozoon following fertilization. Thus, in the fertilized ovum, there are two pronuclei, one originating from the ovum, the other from the spermatozoon that brought about fertilization; they approach each other, but do not fuse until just before the first cleavage, when each pronucleus loses its membrane to release its contents.


chloroplast stroma

The space enclosed by the double membrane of a chloroplast but excluding the thylakoid space. It contains DNA, ribosomes and some temporary products of photosynthesis.


rough endoplasmic reticulum lumen

The volume enclosed by the membranes of the rough endoplasmic reticulum.


perforation plate

A cell wall part that is the part of a wall of a vessel member and bears one or more openings (perforations).


pathogen-containing vacuole lumen

The enclosed volume within the sealed membrane of a pathogen-containing vacuole.


sperm glycocalyx

The carbohydrate rich layer at the outermost periphery of a sperm cell.


cuticular plate

A dense network of actin filaments found beneath the apical cell surface of hair cells, and into which stereocilia are inserted.


type I pilus

A short filamentous structure on the surface of a bacterial cell distinguished from other pili by their D-mannose-sensitive agglutinatination of erythrocytes. In E. coli, type I pili consist of a short tip fibrillum made up of the adhesin protein (FimH) and two minor subunits (FimG and FimF) that is joined to the pilus rod, a homopolymer of ~1000 FimA subunits.


amyloplast membrane

Either of the lipid bilayers that surround an amyloplast and form the amyloplast envelope.


polytene chromosome weak point

A region of the polytene chromosome where the diameter is considerably decreased, probably resulting from local differences in chromosome organization.


cyanelle stroma

The space enclosed by the double membrane of a cyanelle.


neuron projection branch point

The location where a secondary projection arises from a neuron projection.


chloroplast membrane

Either of the lipid bilayers that surround a chloroplast and form the chloroplast envelope.


cell body membrane

The plasma membrane of a cell that bears surface projections such as axons, dendrites, cilia, or flagella, excluding the plasma membrane on cell projections.


proplastid stroma

The space enclosed by the double membrane of a proplastid.


ciliary shaft

The mid part of a cilium between the ciliary base and ciliary tip that extends into the extracellular space.


intracellular immature spore

A cell or part of the cell that constitutes an early developmental stage of a spore, a small reproductive body that is highly resistant to desiccation and heat and is capable of growing into a new organism, produced especially by certain bacteria, fungi, algae, and nonflowering plants.


male pronucleus

The pronucleus originating from the spermatozoa that was involved in fertilization.


rhoptry

A large, club-shaped secretory organelle that forms part of the apical complex of an apicomplexan parasite, and consists of a bulbous body and a narrow electron-dense neck that extends through the conoid at the apical tip of the parasite. The rhoptry necks serve as ducts through which the contents of the rhoptries are secreted after attachment to the host has been completed and at the commencement of invasion. Rhoptry proteins function in the biogenesis and host organellar association of the parasitophorous vacuole.


cortical endoplasmic reticulum lumen

The volume enclosed by the membranes of the cortical endoplasmic reticulum.


striated muscle thin filament

Filaments formed of actin and associated proteins; attached to Z discs at either end of sarcomeres in myofibrils.


gerontoplast stroma

Any plastid stroma that is part of a gerontoplast.


spindle pole body

The microtubule organizing center in fungi; functionally homologous to the animal cell centrosome.


axon initial segment

Portion of the axon proximal to the neuronal cell body, at the level of the axon hillock. The action potentials that propagate along the axon are generated at the level of this initial segment.


pilus tip

The pointed extremity furthest from the cell of a pilus.


meiotic spindle pole

Either of the ends of a meiotic spindle, a spindle that forms as part of meiosis, where spindle microtubules are organized; usually contains a microtubule organizing center and accessory molecules, spindle microtubules and astral microtubules.


subpellicular network

A mechanically stable cytoskeletal structure associated with the cytoplasmic face of the pellicle and surrounding the microtubule-based cytoskeleton.


hydrogenosome lumen

The volume enclosed by the hydrogenosome membrane.


recombination nodule

An electron dense structure that is associated with meiotic chromosomes.


intermediate layer of spindle pole body

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


primary cell wall

A plant cell wall that is still able to expand, permitting cell growth. Primary cell walls contain more pectin than secondary walls and no lignin is present.


inner mucus layer

The inner of two mucus layers secreted by epithelial cells in the colon; the inner mucus layer is firmly attached to the epithelium, is densely packed with a compact stratified appearance and is devoid of bacteria.


S-layer

A crystalline protein layer surrounding some bacteria.


kinociliary basal body

A ciliary basal body that is part of a kinocilium.


pericellular basket

Ramification of basket cell axon surrounding cell bodies, forming the characteristic pericellular baskets from which the cell class derives its name.


half bridge of spindle pole body

Structure adjacent to the plaques of the spindle pole body.


glycoprotein network

An extracellular matrix part that consists of cross-linked glycoproteins.


acidocalcisome

An electron-dense acidic membrane-bounded organelle which contains a matrix of pyrophosphate and polyphosphates with bound calcium and other cations.


endoplasmic reticulum cisternal network

A subcompartment of the endoplasmic reticulum consisting of flattened, disc-shaped domains known as cisternae. These are typically found close to the nucleus and are generally more prominent in secretory cells.


podosome ring

The ring structure surrounding the podosome core, containing proteins such as vinculin and talin.


host cell junction

A plasma membrane part that forms a specialized region of connection between two host cells or between a host cell and the host extracellular matrix. At a host cell junction, anchoring proteins extend through the host plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighboring cells or to proteins in the extracellular matrix.


outer plaque of spindle pole body

One of three laminate structures that form the spindle pole body; the outer plaque is in the cytoplasm.


mitotic spindle midzone

The area in the center of the anaphase spindle consisting of microtubules, microtubule bundling factors and kinesin motors where the spindle microtubules from opposite poles overlap in an antiparallel manner.


mossy fiber rosette

A synapse of a mossy fiber onto the dendrite of a granule cell; each mossy fiber can have up to 50 rosettes.


plastid membrane

Either of the lipid bilayers that surround a plastid and form the plastid envelope.


host cell late endosome membrane

The lipid bilayer surrounding a host cell late endosome.


chloroplast starch grain

Plant storage body for amylose and amylopectin, 1-100um in diameter, and located in chloroplasts. Also contains small amounts of enzymes, amino acids, lipids and nucleic acids. The shape of the grain varies widely amongst species, but is often spherical or disk-shaped.


endexine

The inner part of the exine, which stains.


endoplasmic reticulum tubular network membrane

The membrane of the endoplasmic reticulum tubular network.


acroblast

A cone-shaped structure in the head of a spermatozoon, which is formed by the coalescence of Golgi fragments following the completion of meiosis. The acroblast is situated adjacent to the acrosomal vesicle.


haustorium

A projection from a cell or tissue that penetrates the host's cell wall and invaginates the host cell membrane.


autolysosome lumen

The volume that is enclosed within the autolysosome single-membrane.


dendrite terminus

A structure at the distal end of a dendrite adapted to carry out a specific function, e.g. dendriole.


inner plaque of mitotic spindle pole body

One of three laminate structures that form the mitotic spindle pole body; the inner plaque is in the nucleus.


extraorganismal space

The environmental space outside of an organism; this may be a host organism in the case of parasitic and symbiotic organisms.


basal body patch

The region in the apical portion of multiciliated epithelial cells where the ciliary basal bodies cluster.


cofilin-actin rod

A cellular structure consisting of parallel, hexagonally arranged actin tubules, comprising filamentous actin and disulfide cross-linked cofilin multimers.


pectic matrix

The gel-like pectin matrix consists of the interlinked acidic and neutral pectin networks that are further cross-linked by calcium bridges. Pectins consist largely of long chains of mostly galacturonic acid units (typically 1,4 linkages and sometimes methyl esters). Three major pectic polysaccharides (homogalacturonan, rhamnogalacturonan I and rhamnogalacturonan II) are thought to occur in all primary cell walls.


acidocalcisome membrane

The lipid bilayer surrounding an acidocalcisome.


photoreceptor inner segment membrane

The membrane surrounding the inner segment of a vertebrate photoreceptor. The photoreceptor inner segment contains mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs.


organellar chromatophore intermembrane space

The region between the inner and outer lipid bilayers that surround an organellar chromatophore.


type Is terminal bouton

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


plasmodesmatal plasma membrane

The portion of the plasma membrane surrounding a plasmodesma.


basal labyrinth

A region in the lower half of some cells formed from extensive infoldings of the basal plasma membrane; includes cytoplasm adjacent to the infolded membrane.


axonemal central pair projection

Part of the 9+2 axoneme, that occurs in most motile cilia, consisting of the projections off of the central pair of single microtubules.


mesaxon

Portion of the ensheathing process (either myelin or non-myelin) where the enveloping lips of the ensheathing cell come together so that their apposed plasma membranes run parallel to each other, separated by a cleft 12 nm wide.


filopodium tip

The end of a filopodium distal to the body of the cell.


basal layer of collagen and cuticulin-based cuticle extracellular matrix

The layer of cuticle most closely apposed to the hypodermal cells. The morphology of the basal layer varies with life stage. In adult C. elegans animals, the basal layers is comprised of three sublayers: two fibrous layers whose fibers run in clockwise and counter-clockwise directions meeting one another at a 60 degree angle, and an amorphous basal layer that lies underneath the fibrous layers and directly contacts the hypodermis. In C. elegans dauer and L1 larval stage animals, the basal layer is characterized by a striated pattern that appears to derive from interwoven laminae. An example of this component is found in Caenorhabditis elegans.


macronucleus

A membrane-bounded organelle of ciliated protozoan cells that contains polyploid copies of a portion of the cell's complete genome. Transcription of genes occurs in macronuclei. Some ciliate species may contain multiple macronuclei per cell.


cleavage furrow

The cleavage furrow is a plasma membrane invagination at the cell division site. The cleavage furrow begins as a shallow groove and eventually deepens to divide the cytoplasm.


ventral disc crossbridge

Structure horizontally linking adjacent microribbons of the ventral disc in Giardia species (trophozoite stage). The composition of crossbridges is not fully known yet.


host cell rough endoplasmic reticulum membrane

The lipid bilayer surrounding the host cell rough endoplasmic reticulum.


host cell endosome membrane

The lipid bilayer surrounding a host cell endosome.


cyanelle intermembrane space

The region between the inner and outer lipid bilayers of the cyanelle envelope; includes the peptidoglycan layer.


longitudinal side of cell surface

The side of the cell parallel to the zygotic axis.


metaphase plate

The intracellular plane, located halfway between the poles of the spindle, where chromosomes align during metaphase of mitotic or meiotic nuclear division.


tectum

The layer of sexine which forms a roof over the columella, granules or other infratectal elements.


type IV pilus

A short filamentous structure on the surface of a bacterial cell distinguished from other pili by post-translational N-methylation of the pilin monomers.


lysosomal glycocalyx

The polysaccharide-based coating on the inner side of a lysosomal membrane. It may be involved in protecting the membrane from digestion by lysosomal enzymes.


fusome

A large intracellular spectrin-rich structure that has been found in insect germline cells and mammalian hematopoietic cells. The fusome is an elongated, branched structure, formed from the spherical spectrosome organelle.


periplasmic space

The region between the inner (cytoplasmic) and outer membrane (Gram-negative Bacteria) or cytoplasmic membrane and cell wall (Fungi and Gram-positive Bacteria).


left tetrad

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


cyanelle membrane

Either of the lipid bilayers that surround a cyanelle and form the cyanelle envelope.


striated muscle dense body

A vinculin-containing myofibril attachment structure of striated muscle that connects sarcomeres to the extracellular matrix. In nematode body wall muscle, the dense body performs the dual role of Z-disk and costamere.


bacterial-type flagellum motor

A transmembrane complex embedded in the cytoplasmic membrane which is the motor force, or torque, generator of the bacterial-type flagellum. The motor consists of a membrane-anchored rotor complex surrounded by one or more stator complexes in the cytoplasmic membrane. The stator consists of a hetero-hexameric complex of 2 membrane proteins, A and B, with stoichiometry A4B2. Examples are the H+ driven MotA-MotB stator complex of Escherichia coli and Salmonella enterica, and the Na+ driven PomA-PomB stator complex of Vibrio and Shewanella species. The rotor complex consists of a membrane-anchored ring and the motor switch complex, which controls the direction of flagellar rotation.


omegasome

Omega-shaped (as in the Greek capital letter) intracellular membrane-bounded organelle enriched in phosphatidylinositol 3-phosphate and dynamically connected to the endoplasmic reticulum. Omegasomes are the first step of the formation of autophagosomes via the phagophore assembly sites.


extrachromosomal DNA

DNA structures that are not part of a chromosome.


host cell postsynaptic membrane

A postsynaptic membrane that is part of a host cell. A postsynaptic membrane is a specialized area of membrane facing the presynaptic membrane on the tip of the nerve ending and separated from it by a minute cleft (the synaptic cleft). Neurotransmitters transmit the signal across the synaptic cleft to the postsynaptic membrane.


mating projection tip

The apex of the mating projection in unicellular fungi exposed to mating pheromone; site of polarized growth.


spindle envelope

An organelle envelope that surrounds the chromosomes and the central part of the spindle apparatus during mitosis and meiosis; observed in many invertebrates. The spindle envelope consists of membrane layers, called parafusorial membranes, derived from endoplasmic reticulum membrane; in male meiosis it forms during prometaphase and persists until early in the ensuing interphase.


hyaluranon cable

A cable structure, surrounding some cell types (e.g. proximal or bronchial tubular epithelial cells), and composed of hyaluranon (HA), a ubiquitous connective tissue glycosaminoglycan.


non-growing cell tip

A cell tip at which no growth takes place. For example, in fission yeast the cell end newly formed by cell division does not grow immediately upon its formation, and lacks actin cytoskeletal structures.


periciliary membrane compartment

A plasma membrane region adjacent to the base of eukaryotic cilia and flagella that is enriched in endocytosis-associated proteins and vesicles and that appears to regulate ciliary membrane homeostasis.


starch grain

Plant storage body for amylose and amylopectin, 1-100um in diameter. Also contains small amounts of enzymes, amino acids, lipids and nucleic acids. The shape of the grain varies widely amongst species, but is often spherical or disk-shaped.


host cell smooth endoplasmic reticulum membrane

The lipid bilayer surrounding the host cell smooth endoplasmic reticulum.


photoreceptor proximal connecting cilium

The proximal region of the photoreceptor connecting cilium is similar to the transition zone of unspecialized primary cilia and houses several major transition zone complexes, including NPHP, MKS, and RPGR.


perforant pathway to dendrate granule cell synapse

A neuron to neuron synapse of a pyramidal neuron in the entorhinal cortex onto a granule cell in the dentate gyrus of the hippocampus.


axolemma

The portion of the plasma membrane surrounding an axon; it is a specialized trilaminar random mosaic of protein molecules floating within a fluid matrix of highly mobile phospholipid molecules, 7-8 nm in thickness.


Woronin body

Peroxisome-derived dense-core vesicle that seals septal pores upon hyphal lysis to prevent excessive cytoplasmic loss. It is specific to several genera of filamentous ascomycetes.


meiotic spindle pole body

The microtubule organizing center that forms as part of the meiotic cell cycle; functionally homologous to the animal cell centrosome.


muscle cell projection membrane

The portion of the plasma membrane surrounding a muscle cell projection.


Isp3 layer of spore wall

The outermost layers of the spore wall, as described in Schizosaccharomyces pombe.


granular component

A structure found in the nucleolus, which contains nearly completed preribosomal particles destined for the cytoplasm.


spine mat

A configuration of neuron spines found on ciliary ganglion neurons in the embryonic and adult brain consisting of patches of closely spaced spines lying flat against the soma.


DIM/DIP cell wall layer

A section of the Actinobacterium-type cell wall composed of (phenyl)phthiocerol, phthiodiolone, phthiotriol dimycocerosate, diphthioceranate and other compounds.


microvesicle

An extracellular vesicle released from the plasma membrane and ranging in size from about 100 nm to 1000 nm.


ciliary pro-basal body

The cilary pro-basal body is an immature, partially assembled form of a ciliary basal body found next to the basal body of a cilium. Pro-basal bodies are not capable of nucleating a cilium. As the cell progresses through the cell cycle, continuing assembly will convert the pro-basal body into a mature basal body that is capable of nucleating a cilium.


ciliary inversin compartment

Proximal part of the ciliary shaft to which the inversin protein (also called Inv) specifically localizes. The inversin compartment appears to have a different protein composition than the rest of the cilium, although there is no structure that separates it form the distal part of the cilium.


plastid stroma

The proteinaceous ground substance of plastids.


rhoptry lumen

The volume enclosed by the rhoptry membrane.


plasma membrane respirasome

A respiratory chain located in the plasma membrane of a cell; made up of the protein complexes that form the electron transport system (the respiratory chain), associated with the plasma membrane. The respiratory chain complexes transfer electrons from an electron donor to an electron acceptor and are associated with a proton pump to create a transmembrane electrochemical gradient.


left posteriolateral basal body

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


dendriole

Small dendrites that makes up a brush structure found as the terminal specialization of a dendrite of a unipolar brush cell (UBC).


host cell

A cell within a host organism. Includes the host plasma membrane and any external encapsulating structures such as the host cell wall and cell envelope.


plasma membrane of growing cell tip

Any plasma membrane part that is part of a growing cell tip.


spongiome

A cellular anatomical entity which is a network of tubules and vessicles and is part of the contractile vacuole complex. It is involved in the discharge of water externally. One of its functions is osmoregulatory.


Golgi stack lumen

The volume enclosed by any of the membranes of the thin, flattened cisternae that form the central portion of the Golgi complex.


antipodal cell nucleus

The nucleus of an antipodal cell, one of three cells of the embryo sac in angiosperms, found at the chalazal end of the embryo away from the point of entry of the pollen tube, and its descendents.


sperm midpiece

The highly organized segment of the sperm flagellum which begins at the connecting piece and is characterized by the presence of 9 outer dense fibers (ODFs) that lie outside each of the 9 outer axonemal microtubule doublets and by a sheath of mitochondria that encloses the ODFs and the axoneme; the midpiece terminates about one-fourth of the way down the sperm flagellum at the annulus, which marks the beginning of the principal piece.


costamere

Regular periodic sub membranous arrays of vinculin in skeletal and cardiac muscle cells, these arrays link Z-discs to the sarcolemma and are associated with links to extracellular matrix.


glycogen granule

Cytoplasmic bead-like structures of animal cells, visible by electron microscope. Each granule is a functional unit with the biosynthesis and catabolism of glycogen being catalyzed by enzymes bound to the granule surface.


pollen wall

The wall surrounding a mature pollen grain; a multilayered structure consisting of a pectocellulosic intine surrounded by a sporopollenin-based exine, which itself contains two layers, the inner nexine and the outer sexine.


host cell part

Any constituent part of a host cell. The host is defined as the larger of the organisms involved in a symbiotic interaction.


cellular bud tip

The end of a cellular bud distal to the site of attachment to the mother cell.


slime layer

A slime layer is an easily removed, diffuse, unorganized layer of extracellular material that surrounds a cell. Specifically this consists mostly of exopolysaccharides, glycoproteins, and glycolipids.


DNA replication termination region

A chromosomal region that contains fork pausing elements influencing the progression and merging of DNA replication forks.


sperm head-tail coupling apparatus

A centrosome-based structure consisting of two cylindrical microtubule-based centrioles and associated components which anchors the flagellum to the sperm head.


host cell envelope

An envelope that surrounds a bacterial host cell and includes the host cytoplasmic membrane and everything external, encompassing the host periplasmic space, host cell wall, and host outer membrane if present.