BCMB20002 Lecture Notes - Lecture 4: Steric Effects, Alpha And Beta Carbon, Molecular Geometry

• School: University of Melbourne
• Department: Biochemistry and Molecular Biology
• Course: BCMB20002
• Professor: Terry Mulhern

Document Summary

Double bond is shared between oxygen, the carbonyl carbon and peptide amine nitrogen. Length of peptide bond is 1. 32 (single bond is 1. 49 , double is 1. 27 ). Double bond character gives rigidity and planarity (o, c, n, nh, c ) Our diagrams usually assume double bond character. Can have two distinct orientations, cis (0 ) or trans (180 )(omega) ( (cid:550) ). Trans - alpha carbon on different side atoms that define this torsion angle are c (i-1), c"(i-1), n(i) and c (i) Cis - alpha carbon on the same side. Alpha carbon and delta carbon on the same side = steric clash. But trans peptide bond is more stable (by about 1000) except for pro (more stable by. Trans is slightly more stable than cis, hence dominant. Peptide, polypeptides, and proteins vary in length from several residues to thousands and molecular weight from hundreds of daltons to mda. General rule: number of residues x 110 = molecular weight.