MBB 222 Lecture Notes - Lecture 9: Coiled Coil, Steric Effects, Alpha Helix
30 Mar 2018
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Interactions between atoms in the polypeptide main chain result in repeating secondary structures: the alpha-helix and the beta-sheet. Secondary structures are stabilized by hydrogen bonding, between main chain atoms (i. e. , not side chains). Thus, they are somewhat independent of the amino acid sequence. Turns and loops are also secondary structures but they are not regular/repeating structures like the a-helix and b-sheet. Turns and loops connect a-helices, a-helices with b-strands, and b- strands within b-sheets. The a-helix is a repeating coiled structure stabilized by hydrogen bonds. N c dire(cid:272)tio(cid:374)(cid:895) a-helices have (cid:862)handedness(cid:863) a-helices coil in one direction or another. To determine the handedness of a helix, take each hand, thumb pointed upward, and wrap your fingers around the turns of the helix. Now, twist your hand along the helical turns, following the helix upward in the direction your thumb is pointing. This will only work with one of your hands, the one that corresponds to the handedness of the helix.
