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CELL MEMBRANES- Lipid Bi-layer
Plasma membrane, ER and mitochondria are composed of a lipid bi-layer. Note the railroad track effect of each membrane (arrow). The extracellular space is narrow between the plasma membrane of each structure (1& 2). The lipid bi-layer supports many proteins that function by either operating across the membrane or on just one side or the other. At synapses and gap junctions, the membranes are the closest.