Pepcde bonds must remain essencally planar and

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Unformatted text preview: Val ­Ala ­His ­ or  ­KKGGLVAH ­ EnergeCc constraints on folding of polypepCdes/proteins 1.  Bond lengths and angles don’t change significantly A C ­C or C ­O bond has typical length, for example. 1.  Atoms do not come closer than their van der Waals radii (steric clashes/hindrance are avoided) 2.  PotenCal for hydrogen bonding needs to be saCsfied H ­bond donor needs an acceptor nearby, and vice versa 3.  PepCde bonds must remain essenCally planar and usually have trans configuraCon Planarity of PepCde Bond Peptide Unit R group R group •  Rigidity: hindered rotaCon around the bond connecCng the carbonyl carbon and amide nitrogen •  Cα, C, O, N, H and Cα lie in a plane •  Why? PepCde Bond Electronic Structure •  PepCde bond has parCal double ­bond character –  Two resonance forms •  Cannot rotate freely •  Also has a small electric dipole pointed toward the carbonyl oxygen 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). 9 CHEMISTRY: PA ULING, COREY, BRA NSON 206 PROC. N. A. S. THE STRUCTURE OF PROTEINS: TWO HYDROGEN-BONDED HELICAL (except for the differences in THE POL YPEPTI...
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This test prep was uploaded on 02/25/2014 for the course BIOC 462A taught by Professor Ziegler,baldwin during the Spring '08 term at University of Arizona- Tucson.

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