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MBB222-lecture6 - the lack of rotation around the peptide...

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the lack of rotation around the peptide bond means that flexibility along the backbone of the protein occurs only in the b d h b bonds to the α -carbon peptide backbones are free to rotate around these phi ( Φ ) and psi ( Ψ ) bonds > allows variety in protein folding
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Φ is the angle of rotation about the bond between the amide N is the angle of rotation about the bond between the amide N and the C α Ψ is the angle of rotation about the bond between C α and the carbonyl C these two dihedral angles determine both the path of the polypeptide chain and the conformation of the peptide polypeptide chain and the conformation of the peptide backbone
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Are all combinations of rotational angles possible? a biochemist by the name of Ramachandran wanted to know the same thing – plotted Φ angles vs. Ψ angles for the various amino acids (Ramachandran plot)
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Ramachandran Plot for L-Alanine most favoured regions: dark green - involve no steric overlap less favoured regions: light green - allowed only at the less favoured regions: light green allowed only at the extreme limits for unfavourable atomic contacts ~ 75% of combinations are excluded because of steric interference consider the plots for other amino acids . . .
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Proteome: Proteome: the entire protein complement of an organism – in humans consists of ~ 32 000 different proteins in humans, consists of 32,000 different proteins » constructed from only 20 different amino acids! a protein chain folds into a unique shape / conformation stabilized by interactions between regions of the linear i id amino acid sequence the resulting 3-D structure is required for efficient function (or any function at all, in some cases)
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Secondary Structure:
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