Many of the major hormones in the body are peptides. These hormones can influence enzyme action, metabolism, and physiology. Certain antibiotics and a few anti-tumor agents are also peptides. The artificial sweetener aspartame is a dipeptide composed of aspartic acid and phenylalanine with a methyl group attached at the carboxyl terminal group (L-aspartyl-L-phenylalanine methyl ester). The sequence of amino acid residues in a polypeptide chain is critical for biological function. A single structural change resulted in a dramatic alteration in physiological function. The ability of an enzyme to catalyze a particular reaction depends on its specific shape. It’s a lot like a key and lock; if the key is broken or in a different shape, it won’t open the lock. The receptor sites on cell surfaces must be in a specific shape for polypeptide hormones to interact with the cell. With twenty different amino acids and each polypeptide consisting of hundreds of amino acids, it is no wonder that proteins play such a variety of roles in the human body.
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