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Unformatted text preview: Structure of Proteins (cont.) Secondary Structure 1) the right-handed -helix was discovered by Pauling and Corey, where the side chains are on the outside of the helix and the helix makes one turn every 3.6 amino acids. The C=O group of residue n is H-bonded to the NH group of residue n + 4 . (Fig. 18.5) The hydrogen bonds are parallel to the long axis of the helix. Wool fibers, very flexible and stretchable, are in -helices. 2) the -sheet has interchain H-bonding, running either parallel (adjacent strands running in same direction) or antiparallel (adjacent strands in opposite directions). Silk, not as easily stretched or as flexible as wool, are in -sheets. (Fig. 18.7) Tertiary Structure The bending and folding of the protein in a 3-D shape depends on: 1) disulfide bridge (-SS-), 2) salt bridge (ionic bond) between -NH 3 + and COO- , 3) H- bonding, 4) Hydrophobic interactions (dispersion forces) as those between non-polar regions of the protein. (See examples of each in Fig. 18.9 in text, p. 611)(See examples of each in Fig....
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