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

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

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.


respirasome

The protein complexes that form the electron transport system (the respiratory chain), associated with a cell membrane, usually the plasma membrane (in prokaryotes) or the inner mitochondrial membrane (on eukaryotes). 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.


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.


somatodendritic compartment

The region of a neuron that includes the cell body (cell soma) and dendrite(s), but excludes the axon.


endoplasmic reticulum lumen

The volume enclosed by the membranes of the endoplasmic reticulum.


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.


sarcomere

The repeating unit of a myofibril in a muscle cell, composed of an array of overlapping thick and thin filaments between two adjacent Z discs.


perinuclear region of cytoplasm

Cytoplasm situated near, or occurring around, the nucleus.


subsynaptic reticulum

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


site of polarized growth

Any part of a cell where non-isotropic growth takes place.


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.


nucleoplasm

That part of the nuclear content other than the chromosomes or the nucleolus.


cell body

The portion of a cell bearing surface projections such as axons, dendrites, cilia, or flagella that includes the nucleus, but excludes all cell projections.


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.


mitochondrial inner membrane

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


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.


Z disc

Platelike region of a muscle sarcomere to which the plus ends of actin filaments are attached.


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.


A band

The dark-staining region of a sarcomere, in which myosin thick filaments are present; the center is traversed by the paler H zone, which in turn contains the M line.


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.


actin filament bundle

An assembly of actin filaments that are on the same axis but may be oriented with the same or opposite polarities and may be packed with different levels of tightness.


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.


cis-Golgi network

The network of interconnected tubular and cisternal structures located at the convex side of the Golgi apparatus, which abuts the endoplasmic reticulum.


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.


axoneme

The bundle of microtubules and associated proteins that forms the core of cilia (also called flagella) in eukaryotic cells and is responsible for their movements.


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.


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.


intracellular organelle lumen

An organelle lumen that is part of an intracellular organelle.


microbody lumen

The volume enclosed by the membranes of a microbody.


photoreceptor outer segment

The outer segment of a vertebrate photoreceptor that contains a stack of membrane discs embedded with photoreceptor proteins.


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.


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.


asymmetric synapse

A type of synapse occurring between an axon and a dendritic spine or dendritic shaft. Asymmetric synapses, the most abundant synapse type in the central nervous system, involve axons that contain predominantly spherical vesicles and contain a thickened postsynaptic density. Most or all synapses of this type are excitatory.


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.


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.


nuclear replication fork

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


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.


microbody

Cytoplasmic organelles, spherical or oval in shape, that are bounded by a single membrane and contain oxidative enzymes, especially those utilizing hydrogen peroxide (H2O2).


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.


contractile ring

A cytoskeletal structure composed of filamentous protein that forms beneath the membrane of many cells or organelles, in the plane of cell or organelle division. Ring contraction is associated with centripetal growth of the membrane that divides the cytoplasm of the two daughter cells or organelles.


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.


vesicle membrane

The lipid bilayer surrounding any membrane-bounded vesicle in the cell.


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.


envelope

A multilayered structure surrounding all or part of a cell; encompasses one or more lipid bilayers, and may include a cell wall layer; also includes the space between layers.


apical cytoplasm

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


axonemal central apparatus

Part of the 9+2 axoneme, that occurs in most motile cilia, consisting of the pair of two single central microtubules and their associated structures which include the central pair projections, the central pair bridges linking the two tubules, and the central pair caps which are attached to the distal or plus ends of the microtubules.


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.


postsynaptic membrane

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 cross the synaptic cleft and transmit the signal to the postsynaptic membrane.


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.


ruffle membrane

The portion of the plasma membrane surrounding a ruffle.


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.


Golgi membrane

The lipid bilayer surrounding any of the compartments of the Golgi apparatus.


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.


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.


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.


cluster of actin-based cell projections

A cell part consisting of multiple, closely packed actin-based 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.


postsynaptic specialization

A network of proteins within and adjacent to the postsynaptic membrane. Its major components include neurotransmitter receptors and the proteins that spatially and functionally organize them such as anchoring and scaffolding molecules, signaling enzymes and cytoskeletal components.


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.


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.


photoreceptor inner segment

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


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.


terminal bouton

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


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.


bounding membrane of organelle

The lipid bilayer that forms the outer-most layer of an organelle.


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.


axonal growth cone

The migrating motile tip of a growing nerve cell axon.


plasmodesmatal plasma membrane

The portion of the plasma membrane surrounding a plasmodesma.


lytic vacuole

A vacuole that is maintained at an acidic pH and which contains degradative enzymes, including a wide variety of acid hydrolases.


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.


presynapse

The part of a synapse that is part of the presynaptic cell.


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.


cell leading edge

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


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.


postsynaptic endocytic zone

A stably positioned site of clathrin adjacent and physically attached to the postsynaptic specialization, which is the site of endocytosis of post-synaptic proteins.


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.


actomyosin

Any complex of actin, myosin, and accessory proteins.


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).


mitochondrial matrix

The gel-like material, with considerable fine structure, that lies in the matrix space, or lumen, of a mitochondrion. It contains the enzymes of the tricarboxylic acid cycle and, in some organisms, the enzymes concerned with fatty acid oxidation.


cyanelle membrane

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


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.


growth cone

The migrating motile tip of a growing neuron projection, where actin accumulates, and the actin cytoskeleton is the most dynamic.


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.


mitochondrial intermembrane space

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


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.


stereocilium bundle

A bundle of cross-linked stereocilia, arranged around a kinocilium on the apical surface of a sensory hair cell (e.g. a neuromast, auditory or vestibular hair cell). Stereocilium bundles act as mechanosensory organelles by responding to fluid motion or fluid pressure changes.


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.


replication fork

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


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).


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.


satellite fibril

An axoneme part that is found in the flagella of mammalian sperm and is located in the middle piece between the outer dense fibers (on the concave side of outer dense fibers as seen in cross-section).


chitosan layer of spore wall

The second outermost layer of the spore wall, as described in Saccharomyces.


cell junction

A cellular component that forms a specialized region of connection between two or more cells, or between a cell and the extracellular matrix, or between two membrane-bound components of a cell, such as flagella.


presynaptic grid

A hexagonal array of electron dense particles attached to the cytoplasmic face of the presynaptic membrane.


sperm head plasma membrane

The plasma membrane that is part of the head section of a sperm cell.


ciliary pocket collar

A constriction site at the junction of the plasma, flagellar and flagellar pocket membranes where the flagellum emerges from the cell body. Observed in some unicellular eukaryotic species such as Chlamydomonas, Giardia and Trypanosoma.


rod bipolar cell terminal bouton

A specialized region of the axon terminus portion of a rod bipolar axon. A rod bipolar cell is a neuron found in the retina and having connections with rod photoreceptor cells and neurons in the inner plexiform layer.


vascular endothelial glycocalyx

The carbohydrate-rich layer lining the vascular endothelium connected to the endothelium through a variety of molecules, mainly proteoglycans and glycoproteins. These form a network in which soluble molecules, either plasma- or endothelium-derived, are incorporated.


immunological synapse

An area of close contact between a lymphocyte (T-, B-, or natural killer cell) and a target cell formed through the clustering of particular signaling and adhesion molecules and their associated membrane rafts on both the lymphocyte and the target cell and facilitating activation of the lymphocyte, transfer of membrane from the target cell to the lymphocyte, and in some situations killing of the target cell through release of secretory granules and/or death-pathway ligand-receptor interaction.


basal part of cell

The region of a cell situated near the base. For example, in a polarized epithelial cell, the basal surface rests on the basal lamina that separates the epithelium from other tissue.


capsule

A protective structure surrounding some fungi and bacteria, attached externally to the cell wall and composed primarily of polysaccharides. Capsules are highly organized structures that adhere strongly to cells and cannot be easily removed. Capsules play important roles in pathogenicity, preventing phagocytosis by other cells, adherance, and resistance to dessication.


bacterial-type flagellum hook-filament junction

The region of the bacterial-type flagellum where the hook and filament meet.


female pronucleus

The pronucleus originating from the ovum that is being fertilized.


M band

The midline of aligned thick filaments in a sarcomere; location of specific proteins that link thick filaments. Depending on muscle type the M band consists of different numbers of M lines.


C bouton

Synaptic bouton found in spinal cord on the soma and proximal dendrites of motor neurons.


organelle inner membrane

The inner, i.e. lumen-facing, lipid bilayer of an organelle envelope; usually highly selective to most ions and metabolites.


ciliary basal body

A membrane-tethered, short cylindrical array of microtubules and associated proteins found at the base of a eukaryotic cilium (also called flagellum) that is similar in structure to a centriole and derives from it. The cilium basal body is the site of assembly and remodeling of the cilium and serves as a nucleation site for axoneme growth. As well as anchoring the cilium, it is thought to provide a selective gateway regulating the entry of ciliary proteins and vesicles by intraflagellar transport.


plastid thylakoid lumen

The volume enclosed by a plastid thylakoid membrane.


sporoplasm

The complex infective apparatus corresponding to the central mass of cytoplasm within a spore that is injected into a host cell by various parasitic microorganisms.


sperm principal piece

The segment of the sperm flagellum where the mitochondrial sheath ends, and the outer dense fibers (ODFs) associated with outer axonemal doublets 3 and 8 are replaced by the 2 longitudinal columns of the fibrous sheath (FS) which run the length of the principal piece and are stabilized by circumferential ribs. The principal piece makes up ~2/3 of the length of the sperm flagellum and is defined by the presence of the FS and of only 7 (rather than 9) ODFs which taper and then terminate near the distal end of the principal piece.


cone matrix sheath

A biochemically and structurally distinct domain of the retinal interphotoreceptor matrix that is specifically associated with cone photoreceptor cell inner and outer segments.


nexine

The inner, non-sculptured part of the exine which lies below the sexine.


ring centriole

A ring-like structure observed at the base of the ciliary cap of insect spermatids. This structure may anchor the axoneme to the ciliary cap membrane and/or act as a diffusion barrier, proposed to be analogous to the annulus of mammalian sperm flagellum.


meiotic 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 meiotic 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 meiotic contractile ring is located inside the plasma membrane at the location of the cleavage furrow. In fungal cells, the meiotic contractile ring forms beneath the plasma membrane of the prospore envelope in preparation for completing cytokinesis.


stromule

Thin filamentous structure extending from the surface of all plastid types examined so far, including chloroplast, proplastid, etioplast, leucoplast, amyloplast, and chromoplast. In general, stromules are more abundant in tissues containing non-green plastids, and in cells containing smaller plastids. The primary function of stromules is still unresolved, although the presence of stromules markedly increases the plastid surface area, potentially increasing transport to and from the cytosol. Other functions of stromules, such as transfer of macromolecules between plastids and starch granule formation in cereal endosperm, may be restricted to particular tissues and cell types.


ventral disc lateral crest

Fibrillar repetitive structure surrounding the ventral disc edge in Giardia species (trophozoite stage). The composition of the lateral crest is not fully known yet.


prospore membrane leading edge

The region of the prospore membrane that extends to surround the spore nucleus; coated with specific proteins that are thought to play a role in prospore membrane organization.


main axon

The main axonal trunk, as opposed to the collaterals; i.e., excluding collaterals, terminal, spines, or dendrites.


smooth muscle dense body

Electron-dense region associated with a smooth muscle contractile fiber.


paranode region of axon

An axon part that is located adjacent to the nodes of Ranvier and surrounded by lateral loop portions of myelin sheath.


dendrite membrane

The portion of the plasma membrane surrounding a dendrite.


unicellular trichome branch

A cell projection part that is a branch of a unicellular trichome.


lateral loop

Non-compact myelin located adjacent to the nodes of Ranvier in a myelin segment. These non-compact regions include cytoplasm from the cell responsible for synthesizing the myelin. Lateral loops are found in the paranodal region adjacent to the nodes of Ranvier, while Schmidt-Lantermann clefts are analogous structures found within the compact myelin internode.


peptidoglycan-based cell wall

A protective structure outside the cytoplasmic membrane composed of peptidoglycan (also known as murein), a molecule made up of a glycan (sugar) backbone of repetitively alternating N-acetylglucosamine and N-acetylmuramic acid with short, attached, cross-linked peptide chains containing unusual amino acids. An example of this component is found in Escherichia coli.


An organelle arrangement comprised of the following elements: a mitochondrion positioned near the presynaptic membrane; an electron-dense mitochondrial plaque adjacent to the outer mitochondrial membrane that faces the presynaptic membrane; filament-like elements appearing to link the mitochondrial plaque to a cell-cell junction region (sometimes termed punctum adherens); tubular or vesicular-appearing membrane (also called vesicular chain) interposed among the filaments. Mitochondrion-associated adherens complexes were initially described in the dorsal horn of the spinal cord. They are found in calyces and other large terminals of the auditory brainstem, and in a variety of mammalian species including humans.


mitochondrial intracristal space

The space bounded by the mitochondrial cristae membranes, continuous with the intermembrane space.


pinceau fiber

Dense plexus formed by the descending collaterals of cerebellar basket cells that wrap around a Purkinje cell axonal initial segment.


neuron projection membrane

The portion of the plasma membrane surrounding a neuron projection.


nuclear lumen

The volume enclosed by the nuclear inner membrane.


attachment organelle

A membrane-bounded extension of the cell, originally characterized in Mycoplasma species, that contains an electron-dense core that is part of the cytoskeleton and is oriented lengthwise and ends distally in a bulbous knob (terminal button). Required for adherence to host cells and involved in gliding motility and cell division.


actin cap

Polarized accumulation of cytoskeletal proteins (including F-actin) and regulatory proteins in a cell. An example of this is the actin cap found in Saccharomyces cerevisiae.


nuclear periphery

The portion of the nuclear lumen proximal to the inner nuclear membrane.


cell septum edging

The cell wall material that surrounds the septum in fungal cells.


external encapsulating structure

A structure that lies outside the plasma membrane and surrounds the entire cell or cells. This does not include the periplasmic space.


varicosity

Non-terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters.


annulate lamellae

Stacks of endoplasmic reticulum (ER) membranes containing a high density of nuclear pores, thought to form from excess nuclear membrane components, that have been described in a number of different cells. Annulate lamellar membranes are continuous with and embedded within the ER.


intracellular anatomical structure

A component of a cell contained within (but not including) the plasma membrane. In eukaryotes it includes the nucleus and cytoplasm.


ventral disc dorsal microribbon

Trilaminar structure extending perpendicularly into the cytoplasm along the length of ventral disc microtubules in Giardia species (trophozoite stage). Constituents of dorsal microribbons (also called dorsal ribbons or microribbons) include alpha-coiled-helix proteins approximately 29 to 38 kDa in size. These proteins line the edges of the microribbons but are not found in microtubules. Tubulins are not found in microribbons.


porosome

A permanent cup-shaped structure at the cell plasma membrane in secretory cells. Following a secretory stimulus, secretory vesicles transiently dock and fuse at the base of porosomes and release intravesicular contents dictated by the turgor pressure generated from the swelling of secretory vesicles.


organelle lumen

The internal volume enclosed by the membranes of a particular organelle; includes the volume enclosed by a single organelle membrane, e.g. endoplasmic reticulum lumen, or the volume enclosed by the innermost of the two lipid bilayers of an organelle envelope, e.g. nuclear lumen.


leading edge membrane

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


nuclear outer membrane-endoplasmic reticulum membrane network

The continuous network of membranes encompassing the nuclear outer membrane and the endoplasmic reticulum membrane.


longitudinal sarcoplasmic reticulum

The portion of the free sarcoplasmic reticulum consisting of longitudinal tubules that connect terminal cisternae.


left middle basal body pair

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


pericentriolar material

A network of small fibers that surrounds the centrioles in cells; contains the microtubule nucleating activity of the centrosome.


presynaptic endocytic zone membrane

The region of the presynaptic membrane that is part of the presynaptic endocytic zone - where synaptic vesicles are endocytosed and recycled following release.


cortical endoplasmic reticulum

A cortical network of highly dynamic tubules that are juxtaposed to the plasma membrane and undergo ring closure and tubule-branching movements.


median body

A non-membrane bound, semi-organized microtubule array of unknown function found in Giardia species (trophozoite stage). It is located on the dorsal side of the trophozoite, slightly posterior to the ventral disc.


mononeme

A secretory organelle that forms part of the apical complex; a small, threadlike structure located is close proximity to the subpellicular microtubules. Its contents include a rhomboid protease (PfROM1 in Plasmodium falciparum) that moves from the lateral asymmetric localization to the merozoite apical pole and the posterior pole upon release of merozoites from schizonts.


glyoxysome

A specialized form of peroxisome that contains the enzymes of the glyoxylate pathway. The glyoxysome is found in some plant cells, notably the cells of germinating seeds.


ciliary rootlet

A cytoskeleton-like structure, originating from the basal body at the proximal end of a cilium, and extending proximally toward the cell nucleus. Rootlets are typically 80-100 nm in diameter and contain cross striae distributed at regular intervals of approximately 55-70 nm.


stereocilia tip-link density

An electron-dense plaque at either end of a stereocilia tip link that provides the anchor in the stereocilia membrane.


preprophase band

A dense band of microtubules, 1-3 pm wide, that appears just beneath the cell membrane before the start of cell division in the cells of higher plants. It precedes the onset of prophase and then disappears as mitosis begins, yet it somehow determines the plane of orientation of the new cell plate forming in late telophase and marks the zone of the parental cell wall where fusion with the growing cell plate ultimately occurs.


inner plaque of spindle pole body

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


mating projection septin band

A septin band, i.e. a diffuse ring composed of a series of septin bars running parallel to the long axis of the cell, located at the neck of a shmoo (mating projection).


stereocilia ankle link

A stereocilia coupling link that is composed of a fine filament present in developing stereocilia that couples the bases of individual stereocilia to one another. They are not present in mature stereocilia.


stereocilium base

The tapered base of the stereocilium adjacent to where it joins the hair cell body. This region contains a rootlet comprised of bundled actin filaments which spans the joint and stabilizes the stereocilium.


phagocytic cup base

The older part of the phagocytic cup where the actin cytoskeleton disassembles, allowing early incoming and outgoing vesicular trafficking.


apical complex

A group of cytoskeletal structures and associated membrane-bounded organelles found at the anterior end of adult obligate intracellular protozoan parasites in the phylum Apicomplexa. The apical complex is involved in attachment to and penetration of the host cell, and in parasite proliferation.


microtubule organizing center

An intracellular structure that can catalyze gamma-tubulin-dependent microtubule nucleation and that can anchor microtubules by interacting with their minus ends, plus ends or sides.


ocelloid

Eye-like subcellular structure found in dinoflagellates (a large group of single-celled eukaryotes). Consists of subcellular analogues to a cornea, lens, iris, and retina. Ocelloids are built from pre-existing organelles, including a cornea-like layer made of mitochondria and a retinal body made of anastomosing plastids.


endosome lumen

The volume enclosed by the membrane of an endosome.


exoneme

A dense granule-like organelle of the apical complex of merozoites, released into the parasitophorous vacuole, mediating protease-dependent rupture and parasite exit from the infected erythrocyte.


juxtaparanode region of axon

A region of an axon near a node of Ranvier that is between the paranode and internode regions.


hyphal membrane

A host-derived membrane surrounding the symbiont hypha during infection.


bacterial-type flagellum filament cap

The proteinaceous structure at the distal tip of the bacterial-type flagellar filament.


Organized structure of distinctive morphology and function, bounded by a lipid bilayer membrane and occurring outside the cell.


magnetosome lumen

The volume enclosed by the membrane of a magnetosome.


glutamatergic synapse

A synapse that uses glutamate as a neurotransmitter.


primary cell septum

A cell septum that forms following nuclear division.


postsynaptic density

An electron dense network of proteins within and adjacent to the postsynaptic membrane of an asymmetric, neuron-neuron synapse. Its major components include neurotransmitter receptors and the proteins that spatially and functionally organize them such as anchoring and scaffolding molecules, signaling enzymes and cytoskeletal components.


subplasmalemmal coating

Electron dense material observed coating the cytoplasmic face of the plasma membrane in certain regions of a neuron, e.g., the axon initial segment; the nodal membrane at the Node of Ranvier.


presynaptic active zone

A specialized region of the plasma membrane and cell cortex of a presynaptic neuron; encompasses a region of the plasma membrane where synaptic vesicles dock and fuse, and a specialized cortical cytoskeletal matrix.


cellularization cleavage furrow

A plasma membrane invagination at the site of separation of a multi-nucleate cell or syncytium into individual cells.


basolateral part of cell

The region of a cell situated by the cell sides which interface adjacent cells and near the base. Often used in reference to animal polarized epithelial cells.


stereocilium shaft

The shaft comprises the majority of the length of the stereocilium. This region is notable for the extreme stability of actin filaments, which are highly crosslinked into a parallel bundle.


medial cortical node

A component of the cell division site that contains the mid1, cdr2, wee1, klp8, and blt1 proteins, and is involved in contractile ring localization. Medial cortical node complexes appear as cortical dots in the middle of the cell during interphase, and function to recruit other ring components in early mitosis.


compact myelin

The portion of the myelin sheath in which layers of cell membrane are tightly juxtaposed, completely excluding cytoplasm. The juxtaposed cytoplasmic surfaces form the major dense line, while the juxtaposed extracellular surfaces form the interperiod line visible in electron micrographs.


reservosome matrix

A matrix composed of planar membranes, vesicles and lipid inclusions within the reservosome.


cortical dynamic polarity patch

A region of the cell cortex that contains a higher concentration of growth polarity factors than the surrounding cortex and that changes position over time. An example is found in fission yeast cells during early mating, in which the GTPase Cdc42 dynamically to discrete zones within the cortex prior to shmoo formation.


centrosomal core

The core region of the centrosome, a layered structure containing proteins, surrounded by the centrosomal corona. The core duplicates once per cell cycle at the G2/M transition when two outer layers form the mitotic spindle poles.


stereocilia coupling link

A structure involved in coupling stereocilia to one another in sensory hair cells There are four morphologically distinct types: tip links, horizontal top connectors, shaft connectors and ankle links. Tip links and horizontal top connectors are the only inter-stereocilia links associated with mature cochlea, whereas ankle links appear during development of the auditory hair bundle.


postsynaptic endocytic zone membrane

The region of the postsynaptic membrane that is part of the postsynaptic endocytic zone. This region of membrane is associated with stable clathrin puncta.


germinal vesicle

The enlarged, fluid filled nucleus of a primary oocyte, the development of which is suspended in prophase I of the first meiotic division between embryohood and sexual maturity.


organelle membrane

A membrane that is one of the two lipid bilayers of an organelle envelope or the outermost membrane of single membrane bound organelle.


outer dense plaque of desmosome

The desmosomal part containing plakoglobins, plakophilins, the N-termini of desmoplakins, as well as the cytoplasmic tails of the desmosomal cadherins, which together attach the plaque to the plasma membrane.


ciliary base

Area of the cilium (also called flagellum) where the basal body and the axoneme are anchored to the plasma membrane. The ciliary base encompasses the distal part of the basal body, transition fibers and transition zone and is structurally and functionally very distinct from the rest of the cilium. In this area proteins are sorted and filtered before entering the cilium, and many ciliary proteins localize specifically to this area.


organellar chromatophore thylakoid lumen

The volume enclosed by an organellar chromatophore thylakoid membrane.


etioplast membrane

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


hyphal cell wall

The cell wall surrounding a fungal hypha.


synapse

The junction between an axon of one neuron and a dendrite of another neuron, a muscle fiber or a glial cell. As the axon approaches the synapse it enlarges into a specialized structure, the presynaptic terminal bouton, which contains mitochondria and synaptic vesicles. At the tip of the terminal bouton is the presynaptic membrane; facing it, and separated from it by a minute cleft (the synaptic cleft) is a specialized area of membrane on the receiving cell, known as the postsynaptic membrane. In response to the arrival of nerve impulses, the presynaptic terminal bouton secretes molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane.


Schaffer collateral - CA1 synapse

A synapse between the Schaffer collateral axon of a CA3 pyramidal cell and a CA1 pyramidal cell.


host intracellular region

That space within the plasma membrane of a host cell.


retrotransposon nucleocapsid

A complex of the retrotransposon RNA genome, reverse transcriptase, integrase, and associated molecules required for reproduction and integration of the retrotransposon into the host genome; the main structural molecule of the nucleocapsid is often a gag protein homolog.


stereocilium coat

A glycocalyx on the the endolymphatic surface of a cochlear hair cell that coats the external surface of each stereocilium and maintains a small distance between adjacent stereocilia in the bundle.


symmetric synapse

A synapse that lacks an electron dense postsynaptic specialization. In vertebtrates, these occur primarily on dendrite shafts and neuronal cell bodies and involve persynapses containing clusters of predominantly flattened or elongated vesicles and are typcially inhibitory.


mitochondrial membrane scission site

The site on the mitochondrial membrane where the separation of a single continuous mitochondrial membrane into two membranes occurs as a final step in mitochondrial fission.


extracellular vesicle

Any vesicle that is part of the extracellular region.


acidocalcisome lumen

The volume enclosed by the membranes of an acidocalcisome.


basolateral cytoplasm

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


deep fiber

Inward projections of the cytoskeletal structures of the oral apparatus, which form a fiber that extends past the cytostome into the cytoplasm.


neuron to neuron synapse

A synapse in which pre and post-synaptic cells are neurons.


hinge region between urothelial plaques of apical plasma membrane

A narrow rim of non-thickened membrane in between urothelial plaques in apical plasma membrane.


plant-type vacuole lumen

The volume enclosed within the vacuolar membrane of a vacuole that retains the same shape regardless of cell cycle phase. An example of this is found in Arabidopsis thaliana.


mitochondrial respirasome

The protein complexes that form the mitochondrial electron transport system (the respiratory chain), associated with the inner mitochondrial 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.


bacterial-type flagellum secretion apparatus

A part of the bacterial-type flagellum that is located at the cytoplasmic side of the MS ring and composed of six membrane proteins (FlhA, FlhB, FliP, FliQ, FliR, and FliO, or orthologs thereof) and three soluble proteins (FliI, FliH, and FliJ, or orthologs thereof) in the cytoplasm. It is responsible for secretion of flagellar type III protein substrates, including the proteins of the flagellar rod, hook, and filament.


axon hillock

Portion of the neuronal cell soma from which the axon originates.


annuli extracellular matrix

The extracellular matrix that is a regularly spaced circumferential ridge present in the cortical region of the cuticle. Annuli are delineated by annular furrows and are present throughout the cuticle with the exception of lateral regions where longitudinal alae are present.


synaptonemal complex

A proteinaceous scaffold found between homologous chromosomes during meiosis. It consists of 2 lateral elements and a central element, all running parallel to each other. Transverse filaments connect the lateral elements to the central element.


basal pole of outer hair cell

The end of the outer hair cell which receives and transmits neural signals.


arbuscule

Highly branched symbiont haustoria within host root cortex cells, responsible for nutrient exchange.


host peribacteroid fluid

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


plasma membrane of cell tip

The portion of the plasma membrane surrounding the cell tip.


mitotic spindle pole

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


sarcoplasmic reticulum membrane

The lipid bilayer surrounding the sarcoplasmic reticulum.


serotonergic synapse

A synapse that uses serotonin as a neurotransmitter.


neuronal cell body membrane

The plasma membrane of a neuron cell body - excludes the plasma membrane of cell projections such as axons and dendrites.


apoptotic body

A vesicle containing parts of a dying cell. Apoptotic bodies can be formed during the execution phase of the apoptotic process, when the cell's cytoskeleton breaks up and causes the membrane to bulge outward. These bulges may separate from the cell, taking a portion of cytoplasm with them, to become apoptotic bodies. These are then engulfed by phagocytic cells, and their components recycled. Apoptotic bodies may range in size from 0.8 to 5um.


spindle midzone

The area in the center of the spindle where the spindle microtubules from opposite poles overlap.


mitotic nuclear bridge midzone membrane domain

A nuclear membrane part at the midzone of the mitotic nuclear bridge. The midzone forms a bulge that is enriched in nuclear pores that lack baskets.


basolateral plasma membrane

The region of the plasma membrane that includes the basal end and sides of the cell. Often used in reference to animal polarized epithelial membranes, where the basal membrane is the part attached to the extracellular matrix, or in plant cells, where the basal membrane is defined with respect to the zygotic axis.


microbody membrane

The lipid bilayer surrounding a microbody.


dendritic growth cone

The migrating motile tip of a growing nerve cell dendrite.


blood microparticle

A phospholipid microvesicle that is derived from any of several cell types, such as platelets, blood cells, endothelial cells, or others, and contains membrane receptors as well as other proteins characteristic of the parental cell. Microparticles are heterogeneous in size, and are characterized as microvesicles free of nucleic acids.


right anterior basal body

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


Schmidt-Lanterman incisure

Regions within compact myelin in which the cytoplasmic faces of the enveloping myelin sheath are not tightly juxtaposed, and include cytoplasm from the cell responsible for making the myelin. Schmidt-Lanterman incisures occur in the compact myelin internode, while lateral loops are analogous structures found in the paranodal region adjacent to the nodes of Ranvier.


basal plasma membrane

The region of the plasma membrane located at the basal end of the cell. Often used in reference to animal polarized epithelial membranes, where the basal membrane is the part attached to the extracellular matrix, or in plant cells, where the basal membrane is defined with respect to the zygotic axis.


presynaptic endocytic zone

A specialized region of the plasma membrane and underlying cytoplasm which surround the the active zone, into which synaptic vesicle membranes are recycled following exocytosis. It is especially enriched in endocytic proteins following intense activity.


dendritic spine head

Distal part of the dendritic spine, that carries the post-synaptic density.


extrinsic component of cell outer membrane

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


cell tip

The region at the end of the longest axis of a cylindrical or elongated cell.


central cylinder

A scaffolding structure present within the inner region of the ciliary transition zone. The central cylinder lies between the outer doublet and inner singlet microtubules.


polar nucleus

Either of two nuclei located centrally in a flowering plant embryo sac that eventually fuse to form the endosperm nucleus.


ciliary transition zone

A region of the cilium between the basal body and proximal segment that is characterized by Y-shaped assemblages that connect axonemal microtubules to the ciliary membrane. The ciliary transition zone appears to function as a gate that controls ciliary membrane composition and separates the cytosol from the ciliary plasm.


mitotic actomyosin contractile ring, proximal layer

The region of the mitotic actomyosin ring adjacent to the plasma membrane where membrane bound scaffolds are located.


mating projection actin fusion focus

A focus at the mating projection tip where the cell wall is degraded during conjugation with cellular fusion. Actin filaments form an aster-like structure from this location.


growth cone membrane

The portion of the plasma membrane surrounding a growth cone.


external side of cell wall

The side of the cell wall that is opposite to the side that faces the cell and its contents.


early recombination nodule

An electron dense structure that is associated with meiotic chromosomes in leptotene or zygotene during meiosis I.


bacterial-type flagellum basal body, distal rod, L ring

One of the rings of the bacterial-type flagellar basal body; anchors the basal body to the outer membrane.


right posteriolateral basal body

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


gut granule lumen

The lumen of a gut granule, a lysosome-related organelle contained within the intestinal cells of the nematode C. elegans.


protein storage vacuole lumen

The volume enclosed by the protein storage vacuole membrane.


cone photoreceptor outer segment

The outer segment of a vertebrate cone photoreceptor that contains membrane discs that are contiguous with the ciliary membrane and containing opsin photoreceptor proteins.


autophagosome lumen

The volume enclosed within the autophagosome double-membrane.


plasmodesmatal desmotubule

A tightly wound cylinder of membrane that is located within the plasmodesmal pore and runs the length of the plasmodesma. The desmotubule likely provides a rigid stability to plasmodesmata and confers a fixed diameter and pore size to the plasmodesmal canal, and is linked to the endoplasmic reticulum in each of the adjacent cell.


smooth endoplasmic reticulum lumen

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


sexine

The outer, sculptured layer of the exine, which lies above the nexine.


septal periplasm

The region between the plasma membrane and the cell wall, as found in organisms such as filamentous fungi.


dopaminergic synapse

A synapse that uses dopamine as a neurotransmitter.


platelet dense tubular network membrane

The lipid bilayer surrounding the platelet dense tubular network.


noradrenergic synapse

A synapse that uses noradrenaline as a neurotransmitter.


The part of the sarcoplasmic reticulum membrane that contains calcium release channels, is devoted to calcium release and is juxtaposed to transverse tubule membrane. The junctional sarcoplasmic reticulum membrane consists of the junctional region of the terminal cisterna membrane.


symplast

The interconnected cell membranes and intracellular regions of a plant. The interconnections occur via the plasmodesmata.


postsynaptic specialization of symmetric synapse

A network of proteins within and adjacent to the postsynaptic membrane of a symmetric synapse, consisting of anchoring and scaffolding molecules, signaling enzymes and cytoskeletal components that spatially and functionally organize the neurotransmitter receptors at the synapse. This structure is not as thick or electron dense as the postsynaptic densities found in asymmetric synapses.


endoplasmic reticulum subcompartment

A distinct region of the endoplasmic reticulum.


xanthophore

A chromatophore containing yellow pigment.


perinuclear endoplasmic reticulum membrane

The membrane of the perinuclear endoplasmic reticulum, which is the portion of endoplasmic reticulum, the intracellular network of tubules and cisternae, that occurs near the nucleus.


secondary cell septum

Cell wall structures composed of linear polysaccharides which are deposited at both sides of the primary septum at 90 degrees to the primary septum.


mitotic nuclear bridge stalk

Either of the regions of a mitotic nuclear bridge proximal to the main portion of each daughter nucleus. The nuclear envelope in the stalk regions is depleted of nuclear pore complexes.


cytoplasmic side of nuclear pore

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


right nucleus

One of the two nuclei found in Giardia species (trophozoite stage). It is located on the right side of the cell when viewed from the dorsal side.


dityrosine layer of spore wall

The outermost layer of the spore wall, as described in Saccharomyces.


nuclear lamina

The fibrous, electron-dense layer lying on the nucleoplasmic side of the inner membrane of a cell nucleus, composed of lamin filaments. The polypeptides of the lamina are thought to be concerned in the dissolution of the nuclear envelope and its re-formation during mitosis. The lamina is composed of lamin A and lamin C filaments cross-linked into an orthogonal lattice, which is attached via lamin B to the inner nuclear membrane through interactions with a lamin B receptor, an IFAP, in the membrane.


peripheral region of growth cone

The non-central region or periphery of the migrating motile tip of a growing nerve cell axon or dendrite.


yolk

The cytoplasmic part that serves as a nutrient reserve or energy source for the developing embryo.


basal ring of apical complex

An electron dense ring at the most posterior position of the apical complex, from which the subpellicular microtubules originate; formed during an invasive life cycle stage of an apicomplexan parasite.


chromoplast intermembrane space

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


basal pole of neuron

Portion of a neuron cell soma closest to the point where the basilar dendrite emerges.


rough endoplasmic reticulum cisterna

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


mitotic actomyosin contractile ring, distal actin filament layer

The region of the mitotic actomyosin ring containing actin filaments and cross linkers, myosin motors, and connections to the plasma membrane through the intermediate layer. It is further from the plasma membrane than the intermediate layer which it is adjacent to.


organelle envelope lumen

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


centrosomal corona

An amorphous structure surrounding the core of the centrosome, from which microtubules are nucleated; contains gamma-tubulin.


dendritic branch point

The part of a dendritic tree where it branches, giving rise to a dendritic branch.


upper tip-link density

An electron-dense plaque at the upper end of a stereocilia tip link that provides the anchor in the stereocilia membrane on the side of the stereocilium where the tip link ends.


fungal-type vacuole lumen

The volume enclosed within the vacuolar membrane of a vacuole, the shape of which correlates with cell cycle phase. An example of this structure is found in Saccharomyces cerevisiae.


prospore membrane spindle pole body attachment site

The region of the prospore membrane to which the spindle pole body (SPB) is anchored; the prospore membrane extends from the SPB attachment site to surround the spore nucleus.


right middle basal body pair

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


medial layer of collagen and cuticulin-based cuticle extracellular matrix

The fluid-filled cuticle layer that lies between the cortical and basal layers and is characterized by the presence of regularly spaced columnar struts that lie on either side of the annular furrows and link the two surrounding layers. In C. elegans, a defined medial layer is found only in adult animals.


late endosome lumen

The volume enclosed by the membrane of a late endosome.


apical pole of neuron

Portion of a neuron cell soma closest to the point where the apical dendrite emerges.


cytoskeletal calyx

A large cytoskeletal structure located at the posterior end of the perinuclear theca of a mammalian sperm head. The nucleus is tightly associated with the calyx, which contains calicin and basic cylicin proteins.


host cell presynaptic membrane

A specialized area of membrane of the host axon terminal that faces the plasma membrane of the host neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many host synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon plasma membrane.


somatic ring canal

A stable intercellular bridge between somatic cells. Examples include the intercellular bridges between ovarian follicle cells in insects and between imaginal disc cells in insects.


type III 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. Type III terminal boutons are larger than type II ones.


distal axon

That part of an axon close to and including the growth cone or the axon terminus.


bacterial extracellular vesicle

Small membrane vesicle (< 1 um) that buds off a prokaryotic cell plasma membrane, able to carry proteins, phospholipids, lipopolysaccharides, nucleic acids, viruses, and more. Important in intercellular communication and pathogenesis; can exist within host cells.


dinoflagellate antapical horn

A horn-shaped dinoflagellate antapex found in thecate species.


epicuticle of collagen and cuticulin-based cuticle extracellular matrix

A lipid-containing layer of cuticle that lies between the cortical layer and the surface coat. An example of this component is found in Caenorhabditis elegans.