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Encyclopedia > Exocytosis
Neuron A (transmitting) to neuron B (receiving)1. Mitochondria 2. synaptic vesicle with neurotransmitters 3. Autoreceptor4. Synapse with neurotransmitter released (serotonin) 5. Postsynaptic receptors activated by neurotransmitter (induction of a postsynaptic potential) 6. Calcium channel7. Exocytosis of a vesicle8. Recaptured neurotransmitter
Neuron A (transmitting) to neuron B (receiving)
1. Mitochondria
2. synaptic vesicle with neurotransmitters
3. Autoreceptor
4. Synapse with neurotransmitter released (serotonin)
5. Postsynaptic receptors activated by neurotransmitter (induction of a postsynaptic potential)
6. Calcium channel
7. Exocytosis of a vesicle
8. Recaptured neurotransmitter
Illustration of an axon releasing dopamine.
Illustration of an axon releasing dopamine.

Exocytosis (ek-soh-sy-TOH-sis) is the durable process by which a cell directs secretory vesicles to the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane. Image File history File links Size of this preview: 503 × 599 pixelsFull resolution (642 × 765 pixel, file size: 168 KB, MIME type: image/png) Synaptical transmission (chemical). ... Image File history File links Size of this preview: 503 × 599 pixelsFull resolution (642 × 765 pixel, file size: 168 KB, MIME type: image/png) Synaptical transmission (chemical). ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... In a neuron, synaptic vesicles, also called neurotransmitter vesicles, store the various neurotransmitters that are released during calcium-regulated exocytosis at the presynaptic terminal into the synaptic cleft of a synapse. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a presynaptic and a postsynaptic neuron. ... Illustration of the major elements in a prototypical synapse. ... Serotonin (pronounced ) (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and enterochromaffin cells in the gastrointestinal tract of animals including humans. ... Ion channels are present in the membranes that surround all biological cells. ... Image File history File links Metadata No higher resolution available. ... Image File history File links Metadata No higher resolution available. ... Look up cell membrane in Wiktionary, the free dictionary. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Wikipedia does not yet have an article with this exact name. ... Figure 1: Basic lipid structure. ...

Contents

Types

In multicellular organisms there are two types of exocytosis: 1) Ca2+ triggered non-constitutive and 2) non Ca2+ triggered constitutive. Exocytosis in neuronal chemical synapses is Ca2+ triggered and serves interneuronal signalling. Constitutive exocytosis is performed by all cells and serves the release of components of the extracellular matrix, or just delivery of newly-synthesized membrane proteins that are incorporated in the plasma membrane after the fusion of the transport vesicle. Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical signals into chemical ones. ... Illustration depicting extracellular matrix (basement membrane and interstitial matrix) in relation to epithelium, endothelium and connective tissue In biology, the extracellular matrix (ECM) is the extracellular part of animal tissue that usually provides structural support to the cells in addition to performing various other important functions. ... Look up cell membrane in Wiktionary, the free dictionary. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...


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Steps

Five steps are involved in exocytosis:


Vesicle trafficking

Certain vesicle-trafficking steps require the translocation of a vesicle over a significant distance. For example, vesicles that carry proteins from the Golgi apparatus to the cell surface are likely to use motor proteins and a cytoskeletal track to get close to their target before tethering would be appropriate. Both the actin- and the microtubule-based cytoskeletons are implicated in these processes, along with several motor proteins. Once the vesicles reach their targets, they come into contact with tethering factors that can restrain them. Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... Molecular motors are biological nanomachines and are the essential agents of movement in living organisms. ...


Vesicle tethering

It is useful to distinguish between the initial, loose tethering of vesicles with their targets from the more stable, docking interactions. Tethering involves links over distances of more than about half the diameter of a vesicle from a given membrane surface (>25 nm). Tethering interactions are likely to be involved in concentrating synaptic vesicles at the synapse.


Vesicle docking

The term docking refers to the holding of two membranes within a bilayer's distance of one another (<5-10 nm). Stable docking probably represents several distinct, molecular states: the molecular interactions underlying the close and tight association of a vesicle with its target may include the molecular rearrangements needed to trigger bilayer fusion. A common feature of many proteins that function in vesicle tethering and docking is their propensity to form highly extended, coiled-coil structures. Tethering and docking of a transport vesicle at the target membrane precedes the formation of a tight core SNARE complex. A kind of trap used in trapping. ...


Vesicle priming

In neuronal exocytosis, the term priming has been used to include all of the molecular rearrangements and ATP-dependent protein and lipid modifications that take place after initial docking of a synaptic vesicle but before exocytosis, such that the influx of calcium ions is all that is needed to trigger nearly instantaneous neurotransmitter release. In other cell types, whose secretion is constitutive (i.e. continuous, calcium ion independent, non-triggered) there is no priming. Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ...


Vesicle fusion

The vesicle fusion is driven by SNARE proteins process of merging the vesicle membrane with the target one resulting in release of large biomolecules in the extracellular space (or in case of neurons in the synaptic cleft). A kind of trap used in trapping. ...

The merging of the donor and the acceptor membranes accomplishes three tasks:
  • The surface of the plasma membrane increases (by the surface of the fused vesicle). This is important for the regulation of cell size, e.g., during cell growth.
  • The substances within the vesicle are released into the exterior. These might be waste products or toxins, or signalling molecules like hormones or neurotransmitters during synaptic transmission.
  • Proteins embedded in the vesicle membrane are now part of the plasma membrane. The side of the protein that was facing the inside of the vesicle now faces the outside of the cell. This mechanism is important for the regulation of transmembrane receptors and transporters.

For other uses, see Toxin (disambiguation). ... For other uses, see Hormone (disambiguation). ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... Illustration of the major elements in a prototypical synapse. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ...

External links

Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ...

See also


  Results from FactBites:
 
Exocytosis - Wikipedia, the free encyclopedia (217 words)
Exocytosis is the process of a biological cell's releasing substances into the extracellular fluid (its environment).
Vesicles that contain the substances to be released are transported to the plasma membrane and fuse with it.
Among many factors involved in exocytosis, the soluble NSF receptor (SNARE proteins) are the best-characterized as catalysts of the membrane fusion reaction.
  More results at FactBites »

 
 

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