Cell Structures - The Golgi Apparatus
Created | Updated Jan 28, 2002
Also known as Golgi Bodies (pronounced Gol-jee) and The Golgi Complex, the Golgi Apparatus is a cell organelle discovered by Italian biologist Camillo Golgi in 1898.
The Golgi Apparatus is found only in eukaryotic cells and consists of around half a dozen flattened, single-membraned sacs (cisternae), arranged in layers (lamellae). It is often described as having the appearance of a stack of pancakes although, as the layers are curved, perhaps a stack of size 'A' silicon implants presents an arguably more accurate and pleasing picture. The curvature is always away from the nucleus (the "cis" end of the Golgi Apparatus) and towards the cell membrane (the trans-Golgi). The organelle is roughly 1 µm in diameter and cells may contain more than one apparatus. In general plant cells contain more Golgi Apparati than animal cells (they have a function in building plant cell walls), and secretory cells contain more than non-secretory cells. For example, cells producing saliva and other digestive chemicals contain many Golgi Apparati.
At the onset of cell division the Golgi Apparatus will disappear, breaking up into vesicles which fuse with the endoplasmic reticulum (ER). It will only reappear at the final phase of mitosis (telophase), reforming from the ER.
The function of the Golgi Apparatus is to receive proteins from the rough Endoplasmic Reticulum and lipids from smooth ER, modify, and then despatch them to their appropriate destinations. Vital proteins, required by the ER to function, are delivered to the cis-Golgi along with the production molecules. These are filtered out at the cis-Golgi and returned to the ER.
Movement of proteins and lipids from ER to the cis-Golgi, from layer to layer within the GA, and finally from the trans-Golgi to their destination, is by means of transport vesicles. Vesicles are formed by an area of membrane which produces a bud, containing the molecules, that is subsequently pinched off. This membrane-bound sac will then migrate through the cytoplasm and fuse with the membrane of the recipient organelle, thus delivering its chemical contents. Transport vesicles may be known by other names at various stages in the process, eg shuttle vesicles within the GA, and secretory vesicles when delivering the finished product, but the function is the same.
There is also some evidence that the Golgi cisternae may migrate through the stack, a cis-Golgi cisternae becoming a medial cisternae, and finally a trans-Golgi cisternae.
Proteins and lipids are transported through the cytoplasm in transport vesicles to the cis-Golgi and passed through the GA where they may be altered by the addition of polysaccharide elements, removal of water, emulsification of lipids, etc. to give them their final structure. Formation of glycoproteins by the addition of polysaccharide elements is the main function of the Golgi Apparatus. At the trans-Golgi the finished molecules are sorted and despatched for use, either within the cell as lysosomes (membrane-bound bodies involved in intracellular digestion and the breakdown of molecules), or outwith it as receptor proteins, hormones, digestive enzymes, mucus, etc.
In short, the Golgi Apparatus may be thought of as a multi-line assembly plant:-
Reception: Unwanted deliveries of vital ER proteins are returned, whilst production lipids and proteins are passed on for modification.
Assembly: Proteins and lipids are modified and passed on to the next assembly line.
Despatch: Finished molecules are packaged and sent to their appropriate destinations.
The Golgi Apparatus is found only in eukaryotic cells and consists of around half a dozen flattened, single-membraned sacs (cisternae), arranged in layers (lamellae). It is often described as having the appearance of a stack of pancakes although, as the layers are curved, perhaps a stack of size 'A' silicon implants presents an arguably more accurate and pleasing picture. The curvature is always away from the nucleus (the "cis" end of the Golgi Apparatus) and towards the cell membrane (the trans-Golgi). The organelle is roughly 1 µm in diameter and cells may contain more than one apparatus. In general plant cells contain more Golgi Apparati than animal cells (they have a function in building plant cell walls), and secretory cells contain more than non-secretory cells. For example, cells producing saliva and other digestive chemicals contain many Golgi Apparati.
At the onset of cell division the Golgi Apparatus will disappear, breaking up into vesicles which fuse with the endoplasmic reticulum (ER). It will only reappear at the final phase of mitosis (telophase), reforming from the ER.
The function of the Golgi Apparatus is to receive proteins from the rough Endoplasmic Reticulum and lipids from smooth ER, modify, and then despatch them to their appropriate destinations. Vital proteins, required by the ER to function, are delivered to the cis-Golgi along with the production molecules. These are filtered out at the cis-Golgi and returned to the ER.
Movement of proteins and lipids from ER to the cis-Golgi, from layer to layer within the GA, and finally from the trans-Golgi to their destination, is by means of transport vesicles. Vesicles are formed by an area of membrane which produces a bud, containing the molecules, that is subsequently pinched off. This membrane-bound sac will then migrate through the cytoplasm and fuse with the membrane of the recipient organelle, thus delivering its chemical contents. Transport vesicles may be known by other names at various stages in the process, eg shuttle vesicles within the GA, and secretory vesicles when delivering the finished product, but the function is the same.
There is also some evidence that the Golgi cisternae may migrate through the stack, a cis-Golgi cisternae becoming a medial cisternae, and finally a trans-Golgi cisternae.
Proteins and lipids are transported through the cytoplasm in transport vesicles to the cis-Golgi and passed through the GA where they may be altered by the addition of polysaccharide elements, removal of water, emulsification of lipids, etc. to give them their final structure. Formation of glycoproteins by the addition of polysaccharide elements is the main function of the Golgi Apparatus. At the trans-Golgi the finished molecules are sorted and despatched for use, either within the cell as lysosomes (membrane-bound bodies involved in intracellular digestion and the breakdown of molecules), or outwith it as receptor proteins, hormones, digestive enzymes, mucus, etc.
In short, the Golgi Apparatus may be thought of as a multi-line assembly plant:-
Reception: Unwanted deliveries of vital ER proteins are returned, whilst production lipids and proteins are passed on for modification.
Assembly: Proteins and lipids are modified and passed on to the next assembly line.
Despatch: Finished molecules are packaged and sent to their appropriate destinations.
