In
cell biology
Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and ...
, a vesicle is a structure
within
Within may refer to:
* ''Within'' (William Joseph album) (2004), by pianist William Joseph
* ''Within'' (Embraced album) (2000), by Swedish melodic black metal band Embraced
* Within (company), a virtual reality content and technology company ba ...
or
outside a
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
, consisting of liquid or cytoplasm enclosed by a
lipid bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
. Vesicles form naturally during the processes of secretion (
exocytosis
Exocytosis () is a form of active transport and bulk transport in which a cell transports molecules (e.g., neurotransmitters and proteins) out of the cell ('' exo-'' + ''cytosis''). As an active transport mechanism, exocytosis requires the use o ...
), uptake (
endocytosis
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. E ...
) and transport of materials within the
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
. Alternatively, they may be prepared artificially, in which case they are called
liposome
A liposome is a small artificial vesicle, spherical in shape, having at least one lipid bilayer. Due to their hydrophobicity and/or hydrophilicity, biocompatibility, particle size and many other properties, liposomes can be used as drug deliver ...
s (not to be confused with
lysosomes
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prote ...
). If there is only one
phospholipid bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
, the vesicles are called ''
unilamellar liposome
A unilamellar liposome is a spherical liposome, a vesicle, bounded by a single bilayer of an amphiphilic lipid or a mixture of such lipids, containing aqueous solution inside the chamber. Unilamellar liposomes are used to study biological systems a ...
s''; otherwise they are called ''multilamellar liposomes''.
The membrane enclosing the vesicle is also a
lamellar phase Lamellar phase refers generally to packing of polar-headed long chain nonpolar-tail molecules in an environment of bulk polar liquid, as sheets of bilayers separated by bulk liquid. In biophysics, polar lipids (mostly, phospholipids, and rarely, gly ...
, similar to that of the
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other
organelles
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
within the cell. A vesicle released from the cell is known as an
extracellular vesicle
Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are naturally released from almost all types of cell but, unlike a cell, cannot replicate. EVs range in diameter from near the size of the smallest physically possible unil ...
.
Vesicles perform a variety of functions. Because it is separated from the
cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
, the inside of the vesicle can be made to be different from the cytosolic environment. For this reason, vesicles are a basic tool used by the cell for organizing cellular substances. Vesicles are involved in
metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
, transport, buoyancy control,
and temporary storage of food and enzymes. They can also act as chemical reaction chambers.
![Sarfus](https://upload.wikimedia.org/wikipedia/commons/7/74/Sarfus.LipidVesicles.jpg)
The 2013
Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single prize, but five separate prizes that, accord ...
was shared by
James Rothman
James Edward Rothman (born November 3, 1950) is an American biochemist. He is the Fergus F. Wallace Professor of Biomedical Sciences at Yale University, the Chairman of the Department of Cell Biology at Yale School of Medicine, and the Director ...
,
Randy Schekman
Randy Wayne Schekman (born December 30, 1948) is an American cell biologist at the University of California, Berkeley, former editor-in-chief of ''Proceedings of the National Academy of Sciences'' and former editor of ''Annual Review of Cell and ...
and
Thomas Südhof
Thomas may refer to:
People
* List of people with given name Thomas
* Thomas (name)
* Thomas (surname)
* Saint Thomas (disambiguation)
* Thomas Aquinas (1225–1274) Italian Dominican friar, philosopher, and Doctor of the Church
* Thomas the Ap ...
for their roles in elucidating (building upon earlier research, some of it by their mentors) the makeup and function of cell vesicles, especially in yeasts and in humans, including information on each vesicle's parts and how they are assembled. Vesicle dysfunction is thought to contribute to
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
,
diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...
, some hard-to-treat cases of
epilepsy
Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...
, some cancers and immunological disorders and certain neurovascular conditions.
Types of vesicular structures
Vacuoles
Vacuoles
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
are cellular organelles that contain mostly water.
*
Plant cells
Plant cells are the cells present in green plants, photosynthetic eukaryotes of the kingdom Plantae. Their distinctive features include primary cell walls containing cellulose, hemicelluloses and pectin, the presence of plastids with the capabi ...
have a ''large central vacuole'' in the center of the cell that is used for
osmotic control and
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
storage.
*
Contractile vacuole
A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole.
Overview
The contractile v ...
s are found in certain
protists
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...
, especially those in Phylum ''
Ciliophora
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different ...
''. These vacuoles take water from the cytoplasm and excrete it from the cell to avoid bursting due to
osmotic pressure
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a solution to take in a pure ...
.
Lysosomes
*
Lysosome
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prot ...
s are involved in cellular digestion. Food can be taken from outside the cell into food vacuoles by a process called
endocytosis
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. E ...
. These food vacuoles fuse with lysosomes which break down the components so that they can be used in the cell. This form of cellular eating is called
phagocytosis
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...
.
*Lysosomes are also used to destroy defective or damaged organelles in a process called
autophagy
Autophagy (or autophagocytosis; from the Ancient Greek , , meaning "self-devouring" and , , meaning "hollow") is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent re ...
. They fuse with the membrane of the damaged organelle, digesting it.
Transport vesicles
*Transport vesicles can move molecules between locations inside the cell, e.g., proteins from the rough
endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
to the
Golgi apparatus
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ins ...
.
*Membrane-bound and secreted proteins are made on
ribosomes
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to f ...
found in the
rough endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
. Most of these proteins mature in the
Golgi apparatus
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ins ...
before going to their final destination which may be to
lysosomes
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prote ...
,
peroxisomes
A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen pero ...
, or outside of the cell. These proteins travel within the cell inside of transport vesicles.
Secretory vesicles
Secretory vesicles 440px
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical ...
contain materials that are to be excreted from the cell. Cells have many reasons to excrete materials.
One reason is to dispose of wastes.
Another reason is tied to the function of the cell. Within a larger organism, some cells are specialized to produce certain chemicals. These chemicals are stored in secretory vesicles and released when needed.
Types
*
Synaptic vesicle
In a neuron, synaptic vesicles (or neurotransmitter vesicles) store various neurotransmitters that are released at the synapse. The release is regulated by a voltage-dependent calcium channel. Vesicles are essential for propagating nerve impulse ...
s are located at
presynaptic terminal
Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous syste ...
s in
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s and store
neurotransmitter
A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell.
Neuro ...
s. When a signal comes down an
axon
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...
, the synaptic vesicles fuse with the cell membrane releasing the neurotransmitter so that it can be detected by
receptor
Receptor may refer to:
* Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
molecules on the next nerve cell.
*In animals
endocrine tissues release
hormones
A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...
into the bloodstream. These hormones are stored within secretory vesicles. A good example is an endocrine tissue found in the
islets of Langerhans
The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of ...
in the
pancreas
The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...
. This
tissue contains many cell types that are defined by which hormones they produce.
*Secretory vesicles hold the enzymes that are used to make the
cell wall
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...
s of
plants
Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...
,
protist
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
s,
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and
Archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
cells as well as the
extracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...
of
animal cell
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...
s.
* Bacteria,
Archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
, fungi and parasites release membrane vesicles (MVs) containing varied but specialized toxic compounds and biochemical signal molecules, which are transported to target cells to initiate processes in favour of the microbe, which include invasion of host cells and killing of competing microbes in the same niche.
Extracellular vesicles
Extracellular vesicles
Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are naturally released from almost all types of cell but, unlike a cell, cannot replicate. EVs range in diameter from near the size of the smallest physically possible unilame ...
(EVs) are lipid bilayer-delimited particles produced by all domains of life including complex eukaryotes, both Gram-negative and Gram-positive bacteria, mycobacteria, and fungi.
Types
*
Ectosomes/microvesicles are shed directly from the plasma membrane and can range in size from around 30
nm to larger than a micron in diameter
). These may include large particles such as
apoptotic blebs released by dying cells,
large oncosomes
Large means of great size.
Large may also refer to:
Mathematics
* Arbitrarily large, a phrase in mathematics
* Large cardinal, a property of certain transfinite numbers
* Large category, a category with a proper class of objects and morphisms (or ...
released by some cancer cells, or "
exophers," released by nematode neurons
and mouse cardiomyocytes.
*
Exosomes: membranous vesicles of endocytic origin (30-100 nm diameter).
Different types of EVs may be separated based on density
[ (by gradient ]differential centrifugation
In biochemistry and cell biology, differential centrifugation (also known as differential velocity centrifugation) is a common procedure used to separate organelles and other sub-cellular particles based on their sedimentation rate. Although o ...
), size, or surface markers. However, EV subtypes have an overlapping size and density ranges, and subtype-unique markers must be established on a cell-by-cell basis. Therefore, it is difficult to pinpoint the biogenesis pathway that gave rise to a particular EV after it has left the cell.
In humans, endogenous extracellular vesicles likely play a role in coagulation, intercellular signaling and waste management.[ Free full text] They are also implicated in the pathophysiological processes involved in multiple diseases, including cancer. Extracellular vesicles have raised interest as a potential source of biomarker discovery because of their role in intercellular communication, release into easily accessible body fluids and the resemblance of their molecular content to that of the releasing cells. The extracellular vesicles of (mesenchymal) stem cells, also known as the secretome of stem cells, are being researched and applied for therapeutic purposes, predominantly degenerative, auto-immune
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". P ...
and/or inflammatory diseases.
In Gram-negative bacteria, EVs are produced by the pinching off of the outer membrane; however, how EVs escape the thick cell walls of Gram-positive bacteria, mycobacteria and fungi is still unknown. These EVs contain varied cargo, including nucleic acids, toxins, lipoproteins and enzymes and have important roles in microbial physiology and pathogenesis. In host-pathogen interactions, gram negative bacteria produce vesicles which play roles in establishing a colonization niche, carrying and transmitting virulence factors into host cells and modulating host defense and response.
Ocean cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
have been found to continuously release vesicles containing proteins, DNA and RNA into the open ocean. Vesicles carrying DNA from diverse bacteria are abundant in coastal and open-ocean seawater samples.
Other types
Gas vesicles are used by Archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
, bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
ic microorganisms, possibly to control vertical migration by regulating the gas content and thereby buoyancy
Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
, or possibly to position the cell for maximum solar light harvesting. These vesicles are typically lemon-shaped or cylindrical tubes made out of protein; their diameter determines the strength of the vesicle with larger ones being weaker. The diameter of the vesicle also affects its volume and how efficiently it can provide buoyancy. In cyanobacteria natural selection has worked to create vesicles that are at the maximum diameter possible while still being structurally stable. The protein skin is permeable to gasses but not water, keeping the vesicles from flooding.
Matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
vesicles are located within the extracellular space, or matrix. Using electron microscopy
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
they were discovered independently in 1967 by H. Clarke Anderson and Ermanno Bonucci. These cell-derived vesicles are specialized to initiate biomineralisation
Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues. It is an extremely widespread phenomenon ...
of the matrix in a variety of tissues, including bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
, cartilage
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...
and dentin
Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...
. During normal calcification
Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...
, a major influx of calcium and phosphate ions into the cells accompanies cellular apoptosis
Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...
(genetically determined self-destruction) and matrix vesicle formation. Calcium-loading also leads to formation of phosphatidylserine
Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid and is a component of the cell membrane. It plays a key role in cell cycle signaling, specifically in relation to apoptosis. It is a key pathway for viruses to enter cells via ap ...
:calcium:phosphate complexes in the plasma membrane mediated in part by a protein called annexins
Annexin is a common name for a group of cellular proteins. They are mostly found in eukaryotic organisms (animal, plant and fungi).
In humans, the annexins are found inside the cell. However some annexins (Annexin A1, Annexin A2, and Annexin A5) ...
. Matrix vesicles bud from the plasma membrane at sites of interaction with the extracellular matrix. Thus, matrix vesicles convey to the extracellular matrix calcium, phosphate, lipids and the annexins which act to nucleate mineral formation. These processes are precisely coordinated to bring about, at the proper place and time, mineralization of the tissue's matrix unless the Golgi are non-existent.
Multivesicular body
Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane ca ...
, or MVB, is a membrane-bound vesicle containing a number of smaller vesicles.
Formation and transport
Some vesicles are made when part of the membrane pinches off the endoplasmic reticulum or the Golgi complex. Others are made when an object outside of the cell is surrounded by the cell membrane.
Vesicle coat and cargo molecules
The vesicle "coat" is a collection of proteins that serve to shape the curvature of a donor membrane, forming the rounded vesicle shape. Coat proteins can also function to bind to various transmembrane receptor proteins, called cargo receptors. These receptors help select what material is endocytosed in receptor-mediated endocytosis
Receptor-mediated endocytosis (RME), also called clathrin-mediated endocytosis, is a process by which cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane (invagination). Thi ...
or intracellular transport.
There are three types of vesicle coats: clathrin
Clathrin is a protein that plays a major role in the formation of coated vesicles. Clathrin was first isolated and named by Barbara Pearse in 1976. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. Whe ...
, COPI
COPI is a coatomer, a protein complex that coats vesicles transporting proteins from the ''cis'' end of the Golgi complex
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most ...
and COPII
The Coat Protein Complex II, or COPII, is a group of proteins that facilitate the formation of vesicles to transport proteins from the endoplasmic reticulum to the Golgi apparatus or endoplasmic-reticulum–Golgi intermediate compartment. This ...
. The various types of coat proteins help with sorting of vesicles to their final destination. Clathrin coats are found on vesicles trafficking between the Golgi and plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
, the Golgi and endosome
Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can ...
s and the plasma membrane and endosomes. COPI coated vesicles are responsible for retrograde transport from the Golgi to the ER, while COPII coated vesicles are responsible for anterograde transport from the ER to the Golgi.
The clathrin
Clathrin is a protein that plays a major role in the formation of coated vesicles. Clathrin was first isolated and named by Barbara Pearse in 1976. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. Whe ...
coat is thought to assemble in response to regulatory G protein
G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their act ...
. A protein coat assembles and disassembles due to an ADP ribosylation factor
ADP ribosylation factors (ARFs) are members of the ARF family of GTP-binding proteins of the Ras superfamily. ARF family proteins are ubiquitous in eukaryotic cells, and six highly conserved members of the family have been identified in mammal ...
(ARF) protein.
Vesicle docking
Surface proteins called SNARE
SNARE proteins – " SNAP REceptor" – are a large protein family consisting of at least 24 members in yeasts, more than 60 members in mammalian cells,
and some numbers in plants. The primary role of SNARE proteins is to mediate vesicle fu ...
s identify the vesicle's cargo and complementary SNAREs on the target membrane act to cause fusion of the vesicle and target membrane. Such v-SNARES are hypothesised to exist on the vesicle membrane, while the complementary ones on the target membrane are known as t-SNAREs.
Often SNAREs associated with vesicles or target membranes are instead classified as Qa, Qb, Qc, or R SNAREs owing to further variation than simply v- or t-SNAREs. An array of different SNARE complexes can be seen in different tissues and subcellular compartments, with 36 isoforms currently identified in humans.
Regulatory Rab
Rab âːb( dlm, Arba, la, Arba, it, Arbe, german: Arbey) is an island in the northern Dalmatia region in Croatia, located just off the northern Croatian coast in the Adriatic Sea.
The island is long, has an area of and 9,328 inhabitants (2 ...
proteins are thought to inspect the joining of the SNAREs. Rab protein is a regulatory GTP-binding protein and controls the binding of these complementary SNAREs for a long enough time for the Rab protein to hydrolyse its bound GTP and lock the vesicle onto the membrane.
SNAREs proteins in plants are understudied compared to fungi and animals. The cell botanist Natasha Raikhel has done some of the basic research in this area, including Zheng et al 1999 in which she and her team found AtVTI1a to be essential to Golgi⇄vacuole
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
transport.
Vesicle fusion
Vesicle fusion can occur in one of two ways: full fusion or kiss-and-run fusion Kiss-and-run fusion is a type of synaptic vesicle release where the vesicle opens and closes transiently. In this form of exocytosis, the vesicle docks and transiently fuses at the presynaptic membrane and releases its neurotransmitters across the s ...
. Fusion requires the two membranes to be brought within 1.5 nm of each other. For this to occur water must be displaced from the surface of the vesicle membrane. This is energetically unfavorable and evidence suggests that the process requires ATP, GTP and acetyl-coA
Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for ...
. Fusion is also linked to budding, which is why the term budding and fusing arises.
In receptor downregulation
Membrane proteins serving as receptor
Receptor may refer to:
* Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
s are sometimes tagged for downregulation
In the biological context of organisms' production of gene products, downregulation is the process by which a cell decreases the quantity of a cellular component, such as RNA or protein, in response to an external stimulus. The complementary proc ...
by the attachment of ubiquitin
Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Fo ...
. After arriving an endosome
Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can ...
via the pathway described above, vesicles begin to form inside the endosome, taking with them the membrane proteins meant for degradation; When the endosome either matures to become a lysosome
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prot ...
or is united with one, the vesicles are completely degraded.
Without this mechanism, only the extracellular part of the membrane proteins would reach the lumen of the lysosome
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prot ...
and only this part would be degraded.
It is because of these vesicles that the endosome is sometimes known as a ''multivesicular body''. The pathway to their formation is not completely understood; unlike the other vesicles described above, the outer surface of the vesicles is not in contact with the cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
.
Preparation
Isolated vesicles
Producing membrane vesicles is one of the methods to investigate various membranes of the cell. After the living tissue is crushed into suspension
Suspension or suspended may refer to:
Science and engineering
* Suspension (topology), in mathematics
* Suspension (dynamical systems), in mathematics
* Suspension of a ring, in mathematics
* Suspension (chemistry), small solid particles suspend ...
, various membranes form tiny closed bubbles. Big fragments of the crushed cells can be discarded by low-speed centrifugation and later the fraction of the known origin (plasmalemma
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
, tonoplast
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
, etc.) can be isolated by precise high-speed centrifugation in the density gradient. Using osmotic shock
Osmotic shock or osmotic stress is physiologic dysfunction caused by a sudden change in the solute concentration around a cell, which causes a rapid change in the movement of water across its cell membrane. Under hypertonic conditions - conditions ...
, it is possible temporarily open vesicles (filling them with the required solution) and then centrifugate down again and resuspend in a different solution. Applying ionophores like valinomycin
Valinomycin is a naturally occurring dodecadepsipeptide used in the transport of potassium and as an antibiotic. Valinomycin is obtained from the cells of several '' Streptomyces'' species, '' S. fulvissimus'' being a notable one.
It is a member ...
can create electrochemical gradients comparable to the gradients inside living cells.
Vesicles are mainly used in two types of research:
*To find and later isolate membrane receptors that specifically bind hormones and various other important substances.
*To investigate transport of various ions or other substances across the membrane of the given type. While transport can be more easily investigated with patch clamp
The patch clamp technique is a laboratory technique in electrophysiology used to study ionic currents in individual isolated living cells, tissue sections, or patches of cell membrane. The technique is especially useful in the study of excitabl ...
techniques, vesicles can also be isolated from objects for which a patch clamp is not applicable.
Artificial vesicles
Artificial vesicles are classified into three groups based on their size: small unilamellar liposomes/vesicles (SUVs) with a size range of 20–100 nm, large unilamellar liposomes/vesicles (LUVs) with a size range of 100–1000 nm and giant unilamellar liposomes/vesicles (GUVs) with a size range of 1–200 µm. Smaller vesicles in the same size range as trafficking vesicles found in living cells are frequently used in biochemistry
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
and related fields. For such studies, a homogeneous phospholipid vesicle suspension can be prepared by extrusion or sonication
A sonicator at the Weizmann Institute of Science during sonicationSonication is the act of applying sound energy to agitate particles in a sample, for various purposes such as the extraction of multiple compounds from plants, microalgae and seawe ...
, or by rapid injection of a phospholipid solution into an aqueous buffer solution. In this way, aqueous vesicle solutions can be prepared of different phospholipid composition, as well as different sizes of vesicles. Larger synthetically made vesicles such as GUVs are used for in vitro studies in cell biology
Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and ...
in order to mimic cell membranes. These vesicles are large enough to be studied using traditional fluorescence light microscopy. A variety of methods exist to encapsulate biological reactants like protein solutions within such vesicles, making GUVs an ideal system for the in vitro recreation (and investigation) of cell functions in cell-like model membrane environments. These methods include microfluidic methods, which allow for a high-yield production of vesicles with consistent sizes.
See also
*Bleb (cell biology)
In cell biology, a bleb is a bulge of the plasma membrane of a cell, characterized by a spherical, bulky morphology. It is characterized by the decoupling of the cytoskeleton from the plasma membrane, degrading the internal structure of the cel ...
* Host-pathogen interface
*Membrane contact site Membrane contact sites (MCS) are close appositions between two organelles. Ultrastructural studies typically reveal an intermembrane distance in the order of the size of a single protein, as small as 10 nm or wider, with no clear upper limit. ...
s
*Membrane nanotube
A tunneling nanotube (TNT) or membrane nanotube is a term that has been applied to protrusions that extend from the plasma membrane which enable different animal cells to touch over long distances, sometimes over 100 μm between T cells. Two t ...
*Membrane vesicle trafficking Membrane vesicle trafficking in eukaryotic animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the Golgi body to specific release locations on the inside of the plasma membrane of the secretory ...
*Micelle
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated collo ...
*Microsome
In cell biology, microsomes are heterogeneous vesicle-like artifacts (~20-200 nm diameter) re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; microsomes are not present in healthy, livin ...
*Protocell
A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a stepping-stone toward the origin of life. A central question in evolution is how simple protocells first arose and how they could ...
*Spitzenkörper
The Spitzenkörper (German for pointed body, SPK) is a structure found in fungal hyphae that is the organizing center for hyphal growth and morphogenesis. It consists of many small vesicles and is present in growing hyphal tips, during spore germ ...
, a structure of many small vesicles found in fungal hyphae
References
Further reading
*
External links
Lipids, Membranes and Vesicle Trafficking - The Virtual Library of Biochemistry, Molecular Biology and Cell Biology
{{DEFAULTSORT:Vesicle (Biology And Chemistry)
Membrane biology
Organelles