golgi apparatus ppt

Golgi apparatusThe Golgi apparatus (also Golgi body or Golgi Complex is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi and was named after him. The primary function of the Golgi apparatus is to process and package macromolecules, such as proteins and lipids, after their synthesis. It is particularly important in the processing of proteins for secretion. The Golgi apparatus forms a part of the cellular endomembrane system. The Golgi is composed of stacks of membrane-bound structures known as cisternae.

• The Golgi is composed of stacks of membrane-bound structures known as cisternae A mammalian cell typically contains 40 to 100 stacks. Between four and eight cisternae are usually present in a stack. An individual stack is sometimes called a dictyosome . About four to eight cisternae are usually present in a stack Each cisterna comprises a flattened membrane disk, and carries Golgi enzymes to help or to modify cargo proteins that travel through them.

• The cisternae stack has four functional regions: the cis-Golgi network, medial-Golgi, endo-Golgi, and trans-Golgi network . Vesicles from the endoplasmic reticulum fuse with the network and subsequently progress through the stack to the trans Golgi network, where they are packaged and sent to the required place. The three basic component of golgi apparatus is Cisternae, Tubules, Vesicles. The tubules are array of associated vesicles and anastomosing tubules(30-50nm)surround the dictyosome and radiate from it .The vesicle are of three types a) transitional vesicles,b) secretory vesicles c) Clathrin vesicles.

• Small vesicles: ( transport vesicles)formed from the GER membrane by budding• newly synthesized protein from GER are

transported to the Golgi complex with the transport vesicles

• about 300-800 A in dimeter

• Cisternae: (flattened sacs or saccules)

• The Golgi complex consist of several membrane-bounded stacked, flattened sacs (or cisternae)

• The saccules are disk-like and often slightly curved

(convex and concave surfaces )

Function • Cells synthesize a large number of different

macromolecules. The Golgi apparatus is integral in modifying, sorting, and packaging these macromolecules for cell secretion (exocytosis) or 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. Enzymes within the cisternae are able to modify substances by the addition of carbohydrates (glycosylation) and phosphates (phosphorylation).

• the Golgi imports substances such as nucleotide sugars from the cytosol. The Golgi plays an important role in the synthesis of proteoglycans, which are molecules present in the extracellular matrix of animals. It is also a major site of carbohydrate synthesis .This includes the productions of glycosaminoglycans long unbranched polysaccharides which the Golgi then attaches to a protein synthesised in the endoplasmic reticulum to form proteoglycans .

• The Golgi complex controls trafficking of different types of proteins.

• Some are destined for secretion.

• Others are destined for the extracellular matrix.

• Other proteins, such as lysosomal enzymes, may need to be sorted and sequestered from the remaining constituents because of their potential destructive effects