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Biology Essay 2 Cell membranes are almost made entirely of protein and lipid. The lipid of membranes is phospholipids. Phospholipids have a very similar structure to triglyceride, except that one of the fatty acid groups is replaced by a phosphate group. This molecule has a top part that is composed of a glycerol group to which an ionised phosphate group is attached. This part is known to have hydrophilic properties (water-loving). Below the head there are two long fatty acids, composed of hydrocarbon chains. These fatty acids are known to have hydrophobic properties (Water-hating). When a small batch of phospholipids comes into contact with water, they will float with the hydrocarbon tails exposed above the water forming a monolayer. If more phospholipids are added the molecules arrange themselves in a bilayer with the hydrocarbon tails facing each other. It is called a lipid bilayer (See figure 1 below) Figure 1 Proteins are spread...

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