ABSTRACT
Unlike prokaryotes, eukaryotic cells contain extensive internal machinery for post-translational modification of proteins. This includes internal organelles responsible for considerable modification of translational products, as well as a developed system for the shuttling of these altered proteins to their final destination sites. This highly organized intracellular system is responsible for a num ber of modifications to newly-formed proteins, including 1) glycosylation, 2) myristoylation, 3) palmitylation, 4) phosphorylation, and 5) addition of glycophospholipid anchors, just to m ention a few of the ways in which proteins are altered by this network. The infernal organelles responsible for these processes comprise the rough endoplasmic reticulum (RER), the Golgi stacks, and the trans-Golgi network, as well as the endosomal-lysosomal network for the recycling of cell-surface proteins and receptors. The considerable alteration of proteins by this cellular network is an im portant way in which multicellular organisms have evolved the capacity to organize into highly differentiated cellular arrays which are able to communicate with, and affect, each other. Taken at the simplest level, the single differentiated cell (Figure 3.1), this post translation network provides the m achinery for specifically directing proteins to final sites within the cell — such as the apical m em brane surface, and various cellular organelles — as well as for packaging proteins into secretory bodies for export.
