Introduction: The Structure and Composition of Biomembranes
Membranes play a central role in both the structure and function of all cells, prokaryotic and eukaryotic, plant and animal. Membranes basically define compartments, each membrane associated with an inside and an outside. If this were all they did, membranes would be considerably less interesting than they are. But, membranes not only define compartments, they also determine the nature of all communication between the inside and outside. This may take the form of actual passage of ions or molecules between the two compartments (in and out) or may be in the form of information, transmitted through conformational changes induced in membrane components. In addition, attached to membranes are many cellular enzymes. Some of these enzymes catalyze transmembrane reactions, involving reactants on both sides of the membrane or molecular transport. Others are involved in sequential reactions involving a series of enzymes which are concentrated in the plane of the membrane, thus facilitating efficient interactions. Still other enzymes have membrane-bound substrates and/or are involved in the maintenance or biosynthesis of the membrane. Most of the fundamental biochemical functions in cells involve membranes at some point, including such diverse processes as prokaryotic DNA replication (e.g., refs. 807, 777, 803), protein biosynthesis, protein secretion, bioenergetics, and hormonal responses.
KeywordsLipid Bilayer Sialic Acid Erythrocyte Membrane Electron Density Profile Membrane Isolation
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