Phospholipids are responsible for the dynamic nature of the plasma membrane. In a membrane, a bilayer of phospholipids forms the matrix of the structure, the fatty acid tails of phospholipids face inside, away from water, whereas the phosphate group faces the outside, aqueous side ( Figure). The head is the hydrophilic part, and the tail contains the hydrophobic fatty acids. The hydrophobic tails are sequestered in the middle of the bilayer. The hydrophilic head groups of the phospholipids face the aqueous solution. The phospholipid bilayer is the major component of all cellular membranes. The fatty acid chains are hydrophobic and cannot interact with water, whereas the phosphate-containing group is hydrophilic and interacts with water ( Figure). Both choline and serine attach to the phosphate group at the position labeled R via the hydroxyl group indicated in green.Ī phospholipid is an amphipathic molecule, meaning it has a hydrophobic and a hydrophilic part. Two chemical groups that may modify the phosphate, choline and serine, are shown here. The phosphate may be modified by the addition of charged or polar chemical groups. A phospholipid is a molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone. Phosphatidylcholine and phosphatidylserine are two important phospholipids that are found in plasma membranes. The phosphate group is modified by an alcohol. A phosphate group alone attached to a diaglycerol does not qualify as a phospholipid it is phosphatidate (diacylglycerol 3-phosphate), the precursor of phospholipids. Instead of three fatty acids attached as in triglycerides, however, there are two fatty acids forming diacylglycerol, and the third carbon of the glycerol backbone is occupied by a modified phosphate group ( Figure). Like fats, they are composed of fatty acid chains attached to a glycerol or sphingosine backbone. Phospholipids are major constituents of the plasma membrane, the outermost layer of animal cells.
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