Membranes are fluid. Membrane molecules are held in place by relatively weak hydrophobic interactions. Most of the lipids and some proteins drift laterally in the plane of the membrane, but rarely flip-flop from one phospholipid layer to the other. The lateral movements of phospholipids are rapid, about 2 microns per second. A phospholipid can travel the length of a typical bacterial cell in 1 second. Many larger membrane proteins drift within the phospholipid bilayer, although they move more slowly than the phospholipids. Some proteins move in a very directed manner, perhaps guided or driven by motor proteins attached to the cytoskeleton. Other proteins never move and are anchored to the cytoskeleton. Membrane fluidity is influenced by temperature. As temperatures cool, membranes switch from a fluid state to a solid state as the phospholipids pack more closely.
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This note was uploaded on 01/04/2012 for the course BSC BSC1005 taught by Professor Orlando,rebecca during the Fall '10 term at Broward College.