329 and 330 in a helix the nh bonds and thus the

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Unformatted text preview: α ­helix C=O group of residue n accepts a hydrogen bond from N ­H group of residue n+4 + N ­H group of residue n donates a hydrogen bond to the oxygen of a C=O group n ­4 2 1 6 5 Poten7ally many hydrogen bonds in a helix, depending on its length Berg, Tymoczko & Stryer Fig. 3.29 and 3.30 In a helix, the N ­H bonds and thus the pepHde groups all point one direcHon δ+ H N C + - O δ- The polarity of the H ­bonds and pepHde groups along the helix results in a net helix dipole: the N ­terminal end is slightly posiHve and the C ­terminal end slightly negaHve “ribbon” representation of helix Alpha helices in proteins are almost all right-handed The α-helix has good van der Waals interactions and avoids steric clashes “Ball-and-stick” representation shows a hole down the middle of the helix “Space filling” representation shows that there is no hole— the helix is nicely packed inside, with R groups nicely staggered and packed on the outside 9 Schrader, F., and Leuchtenberger, C., Exp. Cell Res., 1, 421-452 (1950). 10 Pollister, A. W., and Leuchtenberger, C., these PROCEEDINGS, 35, 66-71 (1949). 11 Leuchtenberger, C., Chromosoma, 3,449-473 (1950). 12 Mirsky, A. E., and Ris, H., Nature, 163, 666-667 (1949). THE STRUCTURE OF PROTEINS: TWO HYDROGEN-BONDED HELICAL CONFIGURATIONS OF THE POL YPEPTIDE CHAIN By LINUS PAULING, ROBERT B. COREY, AND H. R. BRANSON* GATES AND CRELLIN LABORATORIES OF CHEMISTRY, CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIFORNIAt VOL. 37, 1951 CHEMISTRY: PA ULING, COREY, BRA NSON PROC. N. A. S. ept for the differences in the side chain R). An amino acid han glycine) has no symmetry elements. The general opersion of one residue of a single chain into a second residue e first is accordingly a rotation about an axis accompa...
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