Golgi apparatus

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Golgi apparatus

The Golgi apparatus (also called the Golgi body, Golgi complex, or dictyosome) is an organelle

Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
found in most eukaryotic

Eukaryote

Animals, plants, fungus, and protists are eukaryotes , organisms whose Cell are organized into complex structures enclosed within Cell membrane....
cells

Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
. It was identified in 1898 by the Italian physician Camillo Golgi

Camillo Golgi

Camillo Golgi was an Italy physician, pathologist and scientist....
and was named after him.

The primary function of the Golgi apparatus is to process and package the macromolecule

Macromolecule

The term macromolecule by definition implies "large molecule". In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles....
s such as 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 and lipid

Lipid

Lipids are broadly defined as any fat-soluble , naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others....
s that are synthesized by the cell.

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Encyclopedia

The Golgi apparatus (also called the Golgi body, Golgi complex, or dictyosome) is an organelle

Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
found in most eukaryotic

Eukaryote

Animals, plants, fungus, and protists are eukaryotes , organisms whose Cell are organized into complex structures enclosed within Cell membrane....
cells

Cell (biology)

Camillo Golgi

Camillo Golgi was an Italy physician, pathologist and scientist....
and was named after him.

The primary function of the Golgi apparatus is to process and package the macromolecule

Macromolecule

Protein

Lipid

Secretion

Secretion is the process of, elaborating and releasing Chemical compound from a cell , or a secreted chemical substance or amount of substance. In contrast to excretion, the substance may have a certain function, rather than being a waste product....
. The Golgi apparatus forms a part of the endomembrane system

Endomembrane system

The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles....
of eukaryotic cells.

Structure

The Golgi is composed of membrane-bound stacks known as cisternae. Between five and eight are usually present; however, in some protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s as many as sixty have been observed.

The cisternae stack has five functional regions: the cis-Golgi network, cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network. Vesicles from the endoplasmic reticulum (via the vesicular-tubular cluster

Vesicular-tubular cluster

A vesicular-tubular cluster , also referred to as the ER-Golgi intermediate compartment , is an organelle in eukaryotic cells. This compartment mediates trafficking between the endoplasmic reticulum and Golgi complex, facilitating the sorting of cargo....
) fuse with the cis-Golgi network and subsequently progress through the stack to the trans-Golgi network, where they are packaged and sent to the required destination. Each region contains different enzymes which selectively modify the contents depending on where they are destined to reside.

The trans face of the trans-Golgi network is the face from which vesicles leave the Golgi. These vesicles then proceed to later compartments such as 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 ....
(or plasma membrane), secretory vesicles or late endosomes.

A cisterna (plural cisternae) comprises a flattened membrane disk that makes up 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....
. A typical Golgi has anywhere from 3 to 7 cisternae stacked upon each other like a stack of dinner plates, but there are usually around 6. The cisternae carry Golgi enzymes to help or to modify cargo proteins traveling through them destined for other parts of the cell.

The cisternae also carry structural proteins important for its maintenance as a flattened membrane and its stacking upon each other.

The earliest cisternae are called the cis-cisternae, followed by the medial cisternae, then the trans-cisternae (as they move away from the endoplasmic reticulum

Endoplasmic reticulum

The endoplasmic reticulum is a eukaryote organelle that forms an interconnected network of tubules, vesicle , and cisternae within cell . The lacey membranes of the endoplasmic reticulum were first seen by Keith R....
).

The formation of new cisternae is often called the cis-Golgi network and at the end of the Golgi where transport to other parts of the cell occurs is called the trans-Golgi network. Both are thought to be specialized cisternae leading in and out of the Golgi apparatus.

Cisternae may also refer to flattened regions of the rough endoplasmic reticulum.

Function

Cells synthesize a large number of different macromolecules required for life. The Golgi apparatus is integral in modifying, sorting, and packaging these substances for cell secretion (exocytosis) or for use within the cell. As an analogy, it is like a cellular post office. It primarily modifies proteins delivered from the rough endoplasmic reticulum but is also involved in the transport of lipid

Lipid

Lysosome

Lysosomes are organelles that contain digestive enzymes . Some biologists say they can only be found in animal cells, but there is new evidence that supports that they may exist in plant cells....
s. In this respect it can be thought of as similar to a post office; it packages and labels items and then sends them to different parts of the cell.

Enzymes within the cisterna

Cisterna

A cisterna comprises a flattened membrane disk that makes up the Golgi apparatus. A typical Golgi has anywhere from 3 to 7 cisternae stacked upon each other like a stack of dinner plates, but there are usually around 6....
e are able to modify substances by the addition of carbohydrates (glycosylation

Glycosylation

Glycosylation is the enzymatic process that links saccharides to produce glycans, either free or attached to proteins and lipids. This enzymatic process produces one of four fundamental components of all cells and also provides a co-translational and post-translational modification mechanism that modulates the structure and function of membr...
) and phosphates (phosphorylation

Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Protein phosphorylation in particular plays a significant role in a wide range of cellular processes....
). In order to do so the Golgi transports substances such as nucleotide sugars into the organelle from the cytosol. Proteins are also labeled with a signal sequence

Protein 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....
of molecules which determine their final destination. For example, the Golgi apparatus adds a mannose-6-phosphate

Mannose

Mannose is a sugar monomer of the hexose series of carbohydrates....
label to proteins destined for lysosome

Lysosome

Lysosomes are organelles that contain digestive enzymes . Some biologists say they can only be found in animal cells, but there is new evidence that supports that they may exist in plant cells....
s.

The Golgi also plays an important role in the synthesis of proteoglycans, molecules present in 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....
of animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s, and it is a major site of carbohydrate

Carbohydrate

Carbohydrates or saccharides are the most abundant of the four major classes of biomolecules. They fill numerous roles in living things, such as the storage and transport of energy and structural components ....
synthesis.

This includes the productions of glycosaminoglycan

Glycosaminoglycan

Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit....
s (GAGs), long unbranched polysaccharide

Polysaccharide

Polysaccharides are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic bonds. They are therefore very large, often branched, macromolecules....
s which the Golgi then attaches to a protein synthesized in the endoplasmic reticulum to form the proteoglycan

Proteoglycan

File:PBB Protein ACAN image.jpgProteoglycans represent a special class of glycoproteins that are heavily glycosylation. They consist of a core protein with one or more covalent bond attached glycosaminoglycan chain....
. Enzymes in the Golgi will polymerize several of these GAGs via a xylose

Xylose

Xylose, or wood sugar, is an aldopentose — a monosaccharide containing five carbon atoms and including an aldehyde functional group. It has chemical formula 5105....
link onto the core protein. Another task of the Golgi involves the sulfation

Sulfation

Sulfation refers to the process whereby a lead-acid battery loses its ability to hold a charge after it is kept in a discharged state too long due to the crystallization of lead sulfate....
of certain molecules passing through its lumen via sulphotranferases that gain their sulphur molecule from a donor called PAPs. This process occurs on the GAGs of proteoglycans as well as on the core protein. The level of sulfation is very important to the proteoglycans' signalling abilities as well as giving the proteoglycan its overall negative charge.

The Golgi is also capable of phosphorylating molecules. To do so it transports ATP

Adenosine triphosphate

This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
into the lumen

Lumen (anatomy)

Kinase

In chemistry and biochemistry, a kinase, alternatively known as a phosphotransferase, is a type of enzyme that transfers phosphate groups from High-energy phosphate donor molecules, such as adenosine triphosphate, to specific target molecules ; the process is termed phosphorylation ...
s, such as casein kinase 1

Casein kinase 1

The Casein kinase 1 family of protein kinases are serine/threonine-selective enzymes that function as regulators of signal transduction pathways in most eukaryotic cell types....
and casein kinase 2

Casein kinase 2

The Casein kinase 2 is a serine/threonine-selective protein kinase that is a tetramer of two alpha subunits and two beta subunits. The alpha subunits have the catalytic kinase domain....
. One molecule that is phosphorylated in the Golgi is Apolipoprotein

Apolipoprotein

Apolipoproteins are proteins that binds to fats . They form lipoproteins, which transport dietary fats through the bloodstream. Dietary fats are digested in the intestine and carried to the liver....
, which forms a molecule known as VLDL that is a constitute of blood serum. It is thought that the phosphorylation of these molecules is important to help aid in their sorting for secretion

Secretion

Secretion is the process of, elaborating and releasing Chemical compound from a cell , or a secreted chemical substance or amount of substance. In contrast to excretion, the substance may have a certain function, rather than being a waste product....
into the blood serum.

The Golgi also has a putative role in apoptosis

Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
, with several Bcl-2

Bcl-2

Bcl-2 is the prototype for a family of mammalian genes and the proteins they produce. They govern mitochondrial outer membrane permeabilization and can be either pro-apoptosis or anti-apoptotic ....
family members localised there, as well as to the mitochondria. In addition a newly characterised anti-apoptotic protein, GAAP (Golgi anti-apoptotic protein), which almost exclusively resides in the Golgi, protects cells from apoptosis by an as-yet undefined mechanism (Gubser et al., 2007).

Vesicular transport

The vesicles that leave the rough endoplasmic reticulum are transported

TRAPP complex

TRAPP is a protein involved in particle transport between organelles....
to the cis face of the Golgi apparatus, where they fuse with the Golgi membrane and empty their contents into the lumen

Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine. By extension, a lumen can also be the inside space of a cellular component or structure, such as the endoplasmic reticulum....
. Once inside they are modified, sorted, and shipped towards their final destination. As such, the Golgi apparatus tends to be more prominent and numerous in cells synthesising and secreting many substances: plasma B cells, the antibody

Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
-secreting cells of the immune system, have prominent Golgi complexes.

Those proteins destined for areas of the cell other than either the endoplasmic reticulum

Endoplasmic reticulum

The endoplasmic reticulum is a eukaryote organelle that forms an interconnected network of tubules, vesicle , and cisternae within cell . The lacey membranes of the endoplasmic reticulum were first seen by Keith R....
or Golgi apparatus are moved towards the trans face, to a complex network of membranes and associated vesicles known as the trans-Golgi network (TGN). This area of the Golgi is the point at which proteins are sorted and shipped to their intended destinations by their placement into one of at least three different types of vesicles, depending upon the molecular marker they carry:

Type	Description	Example
Exocytotic vesicles (continuous)	Vesicle contains proteins destined for extracellular release. After packaging the vesicles bud off and immediately move towards the plasma membrane, where they fuse and release the contents into the extracellular space in a process known as constitutive secretion 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.... .	Antibody Antibody Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses.... release by activated plasma B cells
Secretory vesicles (regulated)	Vesicle contains proteins destined for extracellular release. After packaging the vesicles bud off and are stored in the cell until a signal is given for their release. When the appropriate signal is received they move towards the membrane and fuse to release their contents. This process is known as regulated secretion 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.... .	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 from neuron Neuron Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves.... s
Lysosomal vesicles	Vesicle contains proteins destined for the lysosome Lysosome Lysosomes are organelles that contain digestive enzymes . Some biologists say they can only be found in animal cells, but there is new evidence that supports that they may exist in plant cells.... , an organelle of degradation containing many acid hydrolase Hydrolase In biochemistry, a hydrolase is an enzyme that catalyzes the hydrolysis of a chemical bond. For example, an enzyme that catalyzed the following reaction is a hydrolase:... s, or to lysosome-like storage organelles. These proteins include both digestive enzymes and membrane proteins. The vesicle first fuses with the late endosome Endosome In biology, an endosome is a membrane-bound compartment inside cells, roughly 300-400 Nanometre in diameter when fully mature.... , and the contents are then transferred to the lysosome via unknown mechanisms.	Digestive protease Protease A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain, which form a molecule of protein.... s destined for the lysosome Lysosome Lysosomes are organelles that contain digestive enzymes . Some biologists say they can only be found in animal cells, but there is new evidence that supports that they may exist in plant cells....

Transport mechanism

The transport mechanism

TRAPP complex

TRAPP is a protein involved in particle transport between organelles....
which proteins use to progress through the Golgi apparatus is not yet clear; however a number of hypotheses currently exist. Until recently, the vesicular transport mechanism was favoured but now more evidence is coming to light to support cisternal maturation. The two proposed models may actually work in conjunction with each other, rather than being mutually exclusive. This is sometimes referred to as the combined model.

Cisternal maturation model: the cisternae of the Golgi apparatus move by being built at the cis face and destroyed at the trans face. Vesicles from the endoplasmic reticulum fuse with each other to form a cisterna at the cis face, consequently this cisterna would appear to move through the Golgi stack when a new cisterna is formed at the cis face. This model is supported by the fact that structures larger than the transport vesicles, such as collagen
Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content....
rods, were observed microscopically to progress through the Golgi apparatus. This was initially a popular hypothesis, but lost favour in the 1980s. Recently it has made a comeback, as laboratories at the University of Chicago
University of Chicago

The University of Chicago is a private university located principally in the Hyde Park, Chicago neighborhood of Chicago. Although an older university by the same name existed prior to its founding, the modern University of Chicago credits its founding to the oil magnate John D....
and the University of Tokyo
University of Tokyo

The , abbreviated as , is a major research university located in Tokyo, Japan. The University has 10 faculty with a total of around 30,000 students, 2,100 of whom are foreign....
have been able to use new technology to directly observe Golgi compartments maturing. Additional evidence comes from the fact that COPI
COPI

COPI is a protein that coats vesicle s that transports proteins from the cis end of the Golgi complex to the rough endoplasmic reticulum . This type of transport is termed retrograde transport....
vesicles move in the retrograde direction, transporting ER proteins back to where they belong by recognizing a signal peptide.

Vesicular transport model: Vesicular transport views the Golgi as a very stable organelle
Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
, divided into compartments in the cis to trans direction. Membrane bound carriers transport material between the ER and the different compartments of the Golgi. Experimental evidence includes the abundance of small vesicles (known technically as shuttle vesicles) in proximity to the Golgi apparatus. To direct the vesicles, actin filaments connect packaging proteins to the membrane to ensure that they fuse with the correct compartment.

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