lec_strc3d_2 - Amino Acid Peptide Bond Planar Four levels...

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Four levels of protein structure Amino Acid & Peptide Bond Planar Angles φ & ψ peptide bond planes are joined by the tetrahedral bonds of the C α . • The rotation parameters The rotation parameters are φ and ψ . Protein structure Two structural motifs that arrange the primary structure of proteins into a higher level of organization predominate in proteins: the α -helix and the β -pleated strand. Atomic representations of these secondary structures are shown: •helical ribbon for the α -helix •wide arrow for β -structures. Both of these structures owe their Both of these structures owe their stability to the formation of hydrogen bonds between N–H and O=C functions along the polypeptide backbone Four different graphic representations of the α -helix. (a) As it originally appeared in Pauling’s 1960 The Nature of the Chemical Bond . (b) Showing the arrangement of peptide planes in the helix I - Alpha Helix helix. (c) A space-filling computer graphic presentation. (d) A “ribbon structure” with an inlaid stick figure, showing how the ribbon indicates the path of the polypeptide backbone.
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I - Alpha Helix Keep the R-group out α -helix
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