BiologicalMolecules160-page18 - secondary and tertiary...

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Biological Molecules - 18 Protein shape and structure The polypeptide chain is just the beginning of a protein. Functional proteins undergo further processing to obtain a final functional shape. Some proteins are composed of more than one polypeptide. The surface structure of the protein is critical for its function. The function of many proteins depends on a specific region of the protein that binds to another molecule. Antibodies, critical to the immune system, function by binding to specific regions of the antigen molecules, to deactivate them. An enzyme binds to the substrate (the reactants) at a specific active site on the enzyme. Secondary Structures The ultimate shape of each protein is determined by bonds that form the
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Unformatted text preview: secondary and tertiary protein structure. As peptide bonds are formed, aligning the amino acids, hydrogen bonds form between different amino acids in the chain. This bonding coils the polypeptide into the secondary structure of the protein, most commonly the alpha helix, discovered by Linus Pauling. The ±-helix coils at every 4 th amino acid. ± Helix Pleated Protein Some regions of the polypeptide have portions that lie parallel to each other (still held by hydrogen bonds) instead of in the alpha helix, in which the amino acids' hydrogen bonds form a pleated structure. Fibrous proteins have significant pleated structures....
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