• In 1925, E. Gorter and F. Grendel reasoned that cell membranes must be a phospholipid bilayer two molecules thick. • The molecules in the bilayer are arranged such that the hydrophobic fatty acid tails are sheltered from water while the hydrophilic phosphate groups interact with water. • In 1972, S.J. Singer and G. Nicolson presented a revised model that proposed that the membrane proteins are dispersed and individually inserted into the phospholipid bilayer. • In this fluid mosaic model , the hydrophilic regions of proteins and phospholipids are in maximum contact with water and the hydrophobic regions are in a nonaqueous environment. • A specialized preparation technique, freeze-fracture, splits a membrane along the middle of the phospholid bilayer prior to electron microscopy. • This shows protein particles interspersed with a smooth matrix, supporting the fluid mosaic model. • Membrane molecules are held in place by relatively weak hydrophobic
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