Golgi apparatus

The Golgi body is a membranous structure within the cytoplasm of cells involved with the further modification of carbohydrates, lipids and proteins. It is composed of a series of flattened, parallel chambers - cisternae - close to the cell nucleus and usually, rough endoplasmic reticulum. It is polarized. The cis face is the receptive end that accepts incoming vesicles from the rER; the trans face and particularly an area termed the trans-Golgi network, is involved in carefully forming vesicles and directing them to destinations such as lysosomes and the plasma membrane for exocytosis.

Within the cisternae, molecules are modified e.g.:

• cleavage of polysaccharide chains on proteoglycans
• glycosylation of sugar residues
• phosphorylation of hydrolytic enzymes
• positioning in the correct compartment e.g.:
  • some membrane proteins are confined to the inner leaflet of the lipid bilayer
  • glycosylated proteins are confined to the outer leaflet ready for fusion with the plasma membrane to form glycocalyx