Vesicle (biology)
Encyclopedia
Supramolecular chemistry
Supramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components...
assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes (see micelle
Micelle
A micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre. This phase is...
), or they may be prepared. Artificially prepared vesicles are known as liposome
Liposome
Liposomes are artificially prepared vesicles made of lipid bilayer. Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases. Liposomes are composite structures made of phospholipids and may contain small amounts of other molecules...
s. Most vesicles have specialized functions depending on what materials they contain.
Because vesicles tend to look alike, it is very difficult to tell the difference between different types.
The vesicle is separated from the cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
by at least one phospholipid bilayer. If there is only one phospholipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar.
Vesicles store, transport
Transport
Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...
, or digest
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
cellular
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
products
Product (biology)
In biochemistry, a product is something "manufactured" by an enzyme from its substrate. For example, the products of lactase are galactose and glucose, which are produced from the substrate lactose....
and waste
Waste
Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...
. The membrane enclosing the vesicle is similar to that of the plasma membrane, and vesicles can fuse with the plasma membrane to release their contents outside of the cell. Vesicles can also fuse with other organelles within the cell.
Because it is separated from the cytosol, 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
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, transport, buoyancy control, and enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
storage. They can also act as chemical reaction chambers.
Types of vesicles
Vacuoles
Vacuoles are vesicles which contain mostly water.- Plant cells are known for having a large central vacuole in the center of the cell that is used for osmotic controlOsmoregulationOsmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
and nutrientPlant nutrition'Plant Nutrition is the study of the chemical elements that are necessary for growth. In 1972, E. Epstein defined 2 criteria for an element to be essential for plant growth:# in its absence the plant is unable to complete a normal life cycle or...
storage. - Contractile vacuoleContractile vacuoleA contractile vacuole is a sub-cellular structure involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole....
s are found in certain protists, especially those in Phylum Ciliophora. These vacuoles take water from the cytoplasm and excrete it from the cell to avoid bursting due to osmotic pressureOsmotic pressureOsmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane....
.
Lysosomes
- LysosomeLysosomethumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...
s or "Suicide Cells" are involved in cellular digestion. Food can be taken from outside the cell into food vacuoles by a process called endocytosisEndocytosisEndocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
. 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.
- Lysosomes are also used to destroy defective or damaged organelles in a process called endophagocytosis. 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 reticulumEndoplasmic reticulumThe endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
to the Golgi apparatusGolgi apparatusThe Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
.
- Membrane-bound and secreted proteins are made on ribosomes found in the rough endoplasmic reticulum. Most of these proteins mature in the Golgi apparatusGolgi apparatusThe Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
before going to their final destination which may be to lysosomes, peroxisomes, or outside of the cell. These proteins travel within the cell inside of transport vesicles.
Secretory vesicles
Secretory vesicles 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. Some examples include the following.
Types of secretory vesicles
- Synaptic vesicleSynaptic vesicleIn a neuron, synaptic 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 impulses between neurons and are constantly recreated by the cell...
s are located at presynaptic terminals in neurons and store neurotransmitterNeurotransmitterNeurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
s. When a signal comes down an axonAxonAn axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
, the synaptic vesicles fuse with the cell membrane releasing the neurotransmitter so that it can be detected by receptorReceptor (biochemistry)In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
molecules on the next nerve cell.
- In animals endocrine tissuesEndocrine systemIn physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...
release hormones into the bloodstream. These hormones are stored within secretory vesicles. A good example is the endocrine tissue found in the islets of LangerhansIslets of LangerhansThe islets of Langerhans are the regions of the pancreas that contain its endocrine cells. Discovered in 1869 by German pathological anatomist Paul Langerhans at the age of 22, the islets of Langerhans constitute approximately 1 to 2% of the mass of the pancreas...
in the pancreasPancreasThe pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
. This tissueTissue (biology)Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
contains many cell types that are defined by which hormones they produce.
- Secretory vesicles hold the enzymes that are used to make the cell wallCell wallThe cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s of plantsPlant cellPlant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic organisms. Their distinctive features include:...
, protistProtistProtists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s, fungi, bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, and ArchaeaArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
cells as well as the extracellular matrixExtracellular matrixIn biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
of animal cells.
Other types of vesicles
- Gas vesicles are used by ArchaeaArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
, bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and planktonPlanktonPlankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic microorganisms, possibly to control vertical migration by regulating the gas content and thereby buoyancy, or possibly to position the cell for maximum solar light harvesting.
- MatrixExtracellular matrixIn biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
vesicles are located within the extracellular space, or matrix. Using electron microscopy but working independently, they were discovered in 1967 by H. Clarke Anderson and Ermanno Bonucci. These cell-derived vesicles are specialized to initiate biomineralisationBiomineralisationBiomineralization 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; all six taxonomic kingdoms contain members that are able to form minerals, and over 60...
of the matrix in a variety of tissues, including boneBoneBones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
, cartilageCartilageCartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
, and dentinDentinDentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
. During normal calcificationCalcificationCalcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
, a major influx of calcium and phosphate ions into the cells accompanies cellular apoptosisApoptosisApoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
(genetically determined self-destruction) and matrix vesicle formation. Calcium-loading also leads to formation of phosphatidylserinePhosphatidylserinePhosphatidylserine is a phospholipid component, usually kept on the inner-leaflet of cell membranes by an enzyme called flippase...
:calcium:phosphate complexes in the plasma membrane mediated in part by a protein called annexins. 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 bodyEndosomeIn biology, an endosome is a membrane-bound compartment inside eukaryotic cells. It is a compartment of the endocytic membrane transport pathway from the plasma membrane to the lysosome. Molecules internalized from the plasma membrane can follow this pathway all the way to lysosomes for...
, or MVB, is a membrane-bound vesicle containing a number of smaller vesicles.
Vesicle formation and transport
Capturing cargo molecules
The assembly of vesicles requires numerous coats to surround and bind to the proteins being transported. these bind to the coat vesicle. They also trap various transmembrane receptor proteins,called cargo receptors,which in turn trap the cargo molecules.Vesicle coat
The vesicle coat serves to sculpt the curvature of a donor membrane, and to select specific proteins as cargo. It selects cargo proteins by binding to sorting signalsProtein targeting
Protein targeting or protein sorting is the mechanism by which a cell transports proteins to the appropriate positions in the cell or outside of it. Sorting targets can be the inner space of an organelle, any of several interior membranes, the cell's outer membrane, or its exterior via secretion...
. In this way the vesicle coat clusters selected membrane cargo proteins into nascent vesicle buds.
There are three types of vesicle coats: clathrin
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 1975. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskelia interact they form a polyhedral lattice...
, COPI
COPI
COPI is a protein complex that coats vesicles transporting proteins from the cis end of the Golgi complex back to the rough endoplasmic reticulum , where they were originally synthesized and between golgi compartments. This type of transport is termed as retrograde transport...
and COPII
COPII
COPII is a type of vesicle coat protein that transports proteins from the rough endoplasmic reticulum to the Golgi apparatus. This is termed anterograde transport. The name "COPII" refers to the specific coat protein complex that initiates the budding process...
. Clathrin coats are found on vesicles trafficking between the Golgi
Golgi
Golgi may refer to:*Camillo Golgi , Italian physician and scientist after which the following terms are named:**Golgi apparatus , an organelle in the eukaryotic cell...
and plasma membrane, the Golgi and endosome
Endosome
In biology, an endosome is a membrane-bound compartment inside eukaryotic cells. It is a compartment of the endocytic membrane transport pathway from the plasma membrane to the lysosome. Molecules internalized from the plasma membrane can follow this pathway all the way to lysosomes for...
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
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 1975. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskelia interact they form a polyhedral lattice...
coat is thought to assemble in response to regulatory G protein
G protein
G proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...
. A coatomer coat assembles and disassembles due to an ARF
ADP ribosylation factor
ADP Ribosylation Factors 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 mammalian cells. Although ARFs are soluble, they generally...
protein.
Vesicle docking
Surface markers called SNARESnare
Snare may refer to:* Snare trap, a kind of trap used for capturing animals* Snare drum* SNARE , a family of proteins involved in vesicle fusion* The Snares, a group of islands approximately 200 kilometres south of New Zealand...
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 (G-protein)
The Rab family of proteins is a member of the Ras superfamily of monomeric G proteins. Approximately 70 types of Rabs have now been identified in humans. Rab GTPases regulate many steps of membrane traffic, including vesicle formation, vesicle movement along actin and tubulin networks, and membrane...
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.
Vesicle fusion
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 unfavourable, and evidence suggests that the process requires ATP, GTP and acetyl-coA, fusion is also linked to budding, which is why the term budding and fusing arises.Vesicles in receptor downregulation
Membrane proteins serving as receptorReceptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
s are sometimes tagged for downregulation by the attachment of ubiquitin
Ubiquitin
Ubiquitin is a small regulatory protein that has been found in almost all tissues of eukaryotic organisms. Among other functions, it directs protein recycling.Ubiquitin can be attached to proteins and label them for destruction...
. After arriving an endosome
Endosome
In biology, an endosome is a membrane-bound compartment inside eukaryotic cells. It is a compartment of the endocytic membrane transport pathway from the plasma membrane to the lysosome. Molecules internalized from the plasma membrane can follow this pathway all the way to lysosomes for...
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
Lysosome
thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...
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
Lysosome
thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...
, 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
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
.
Vesicle preparation
Phospholipid vesicles have been studied in biochemistryBiochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
. For such studies, a homogeneous phospholipid vesicle suspension can be prepared by sonication
Sonication
thumb|right|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. In the laboratory, it is usually applied using an ultrasonic bath or an ultrasonic probe, colloquially known as...
, injection of a phospholipid solution into the aqueous buffer solution membranes. In this way aqueous vesicle solutions can be prepared of different phospholipid composition, as well as different sizes of vesicles.
See also
- Endoplasmic reticulumEndoplasmic reticulumThe endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
- Golgi apparatusGolgi apparatusThe Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
- MicelleMicelleA micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre. This phase is...
- Membrane nanotubeMembrane nanotubeMembrane nanotubes, membrane nanotubules or cytonemes are long and thin tubes formed from the plasma membrane that connect different animal cells over long distances. Two types of nanotubes have been observed. The first type are less than 0.7 micrometres in diameter, contain actin and carry...
- EndocytosisEndocytosisEndocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
- Synaptic vesicleSynaptic vesicleIn a neuron, synaptic 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 impulses between neurons and are constantly recreated by the cell...
- Membrane contact siteMembrane contact siteMembrane contact sites are areas within a cell where the membranes of two organelles are arranged in close proximity . These sites are thought to be important in the transport of small molecules such as lipids between organelles, and offer an alternative to the classical mechanism of lipid...
s - SpitzenkörperSpitzenkörperThe Spitzenkörper is a structure found in fungal hyphae which is the organizing center for hyphal growth and morphogenesis. It consists of many small vesicles and is present in growing hyphal tips, during spore germination and where branch formation occurs. Its position in the hyphal tip correlates...
- DODABDODABDioctadecyldimethylammonium bromide is a doublechained quaternary ammonium surfactant that forms unilamellar vesicles in water. Among various preparation methods, the ‘‘hot-water” method offers a simple procedure to prepare DODAB cationic vesicles by simply dissolving the DODAB in hot water...