BIOL 0280 Lecture Notes - Lecture 2: Steric Effects, Protein Structure, Electric Dipole Moment
7 Nov 2016
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Secondary structure: short segments of protein that adopt a particular predefined configuration such as a helix, a sheet, a turn, random coil. The partial double-bond character makes the peptide bond planar. The carbonyl o has a partial (-) and amide n has a partial (+) --> small electric dipole. Virtually all peptide bonds in proteins occur in this trans configuration, giving the bulky substituents on a-c the most room. Steric hindrance in cis-peptide bonds --> would be very difficult due to bulky side chains. *for proline, because it is also bonded to the n, can have cis or trans forms. The peptide bond angle between the a-amino n and carboxyl c is fixed. Phi: angle of bond between a-c and a-amino n. Psi: angle of bond between a-c and carboxyl c (from n-->c terminus, first angle you come to is phi, second is psi) These angles refer to the rotation of the planes relative to the side chains.
