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Exocytosis (ek-soh-sy-TOH-sis, Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
: ??? - external and ??t?? - cell) is the durable process by which a cell directs the contents of secretory vesicles
Vesicle (biology)

A vesicle is a small bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell....
 out of the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
. 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.

ulticellular 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.






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Exocytosis (ek-soh-sy-TOH-sis, Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
: ??? - external and ??t?? - cell) is the durable process by which a cell directs the contents of secretory vesicles
Vesicle (biology)

A vesicle is a small bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell....
 out of the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
. 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.

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
Extracellular matrix

In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal Cell in addition to performing various other important functions....
, or just delivery of newly-synthesized membrane proteins that are incorporated in the plasma membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
 after the fusion of the transport vesicle
Vesicle (biology)

A vesicle is a small bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell....
. Exocytosis is the opposite of endocytosis
Endocytosis

Endocytosis is the process by which cell s absorb material from outside the cell by engulfing it with their cell membrane. It is used by all cells of the body because most substances important to them are large Chemical polarity molecules that cannot pass through the hydrophobic plasma membrane or cell membrane....
.

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
Golgi apparatus

The Golgi apparatus is an organelle found in most eukaryote Cell . It was identified in 1898 by the Italian physician Camillo Golgi and was named after him....
 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 cytoskeleton's are implicated in these processes, along with several motor proteins
Molecular motors

Molecular motors are biological molecular machines that are the essential agents of movement in living organisms. Generally speaking, a motor may be defined as a device that consumes energy in one form and converts it into motion or Mechanical work; for example, many protein-based molecular motors harness the chemical Gibbs free energy releas...
. Once the vesicles reach their targets, they come into contact with tethering factors that can restrain them.

Vesicle tethering

It is useful to distinguish between the initial, loose tethering of vesicles with their targets from the more stable, packing 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
Snare

A Trapping #Snares is a kind of trap used for capturing animals. It may also mean:* Snare drum* SNARE , a family of proteins involved in vesicle fusion...
.

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
Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
 release. In other cell types, whose secretion is constitutive (i.e. continuous, calcium ion independent, non-triggered) there is no priming.

Vesicle fusion

The vesicle fusion is driven by SNARE
Snare

A Trapping #Snares is a kind of trap used for capturing animals. It may also mean:* Snare drum* SNARE , a family of proteins involved in vesicle fusion...
 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).

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 toxin
    Toxin

    A toxin is a poisonous substance produced by living cells or organisms. For a toxic substance not produced by living organisms, "toxicant" is the more appropriate term, and "toxics" is an acceptable plural....
    s, or signalling molecules like hormone
    Hormone

    Hormones are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism....
    s or neurotransmitter
    Neurotransmitter

    Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
    s during synaptic transmission.
  • Protein
    Protein

    Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
    s 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
    Receptor (biochemistry)

    In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
     and transporters.


External links


See also

  • Secretory pathway
    Secretory pathway

    The secretory pathway is a series of steps a Cell uses to move proteins out of the cell; a process known as secretion. The path of a protein destined for secretion has its origins in the rough endoplasmic reticulum, a membrane bound Cellular_compartment in the cell....
  • Synapse
  • Endocytosis
    Endocytosis

    Endocytosis is the process by which cell s absorb material from outside the cell by engulfing it with their cell membrane. It is used by all cells of the body because most substances important to them are large Chemical polarity molecules that cannot pass through the hydrophobic plasma membrane or cell membrane....
  • Endocytic cycle
    Endocytic cycle

    Most animal cells take up portions of their surface plasma membranes in a process called endocytosis. The main route of endocytosis is the coated pit which buds into a cell to form a cytoplasmic vesicle ? a clathrin-coated vesicle....
  • Membrane nanotube
    Membrane nanotube

    Membrane nanotubes or membrane nanotubules or cytonemes are long and thin tubes formed from the plasma membrane that connect different animal cells over long distances....