Golgi apparatus.
Cells synthesise 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. It primarily modifies proteins delivered from the rough endoplasmic reticulum, but is also involved in the transport of lipids around the cell, and the creation of lysosomes. 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 cisternae are able to modify substances by the addition of carbohydrates (glycosylation) and phosphate (phosphorylation) to them. In order to do so the Golgi transports substances such as nucleotide sugars into the organelle from the cytosol. Proteins are also labelled with a signal sequence of molecules which determine their final destination. For example, the Golgi apparatus adds a mannose-6-phosphate label to proteins destined for lysosomes.
The Golgi also plays an important role in the synthesis of proteoglycans, molecules present in the extracellular matrix of animals, and it is a major site of carbohydrate synthesis.[3]
This includes the productions of glycosaminoglycans or GAGs, long unbranched polysaccharides which the Golgi then attaches to a protein synthesized in the endoplasmic reticulum to form the proteoglycan.[4]Enzymes in the Golgi will polymerize several of these GAGs via a xylose link onto the core protein. Another task of the Golgi involves the sulfation 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.[3]
The Golgi is also capable of phosphorylating molecules. To do so it transports ATP into the lumen.[5] The Golgi itself contains resident kinases, such as casein kinases. One molecule that is phosphorylated in the Golgi is Apolipoprotein, 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 of secretion into the blood serum.[6]
The Golgi also has a putative role in apoptosis, with several Bcl-2 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.
Lysosomes are organelles that contain digestive enzymes (acid hydrolases). They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are built in the Golgi apparatus. The name lysosome derives from the Greek words lysis, which means dissolution or destruction, and soma, which means body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in autolysis.
2007-09-03 06:43:15
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answer #1
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answered by ? 3
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Can we say cut and paste.
Just go here:
http://en.wikipedia.org/wiki/Lysosomes
2007-09-03 13:50:37
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answer #2
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answered by David 4
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