Protein Secondary Structure Section C
PRIMARY STRUCTURE OF PROTEINS
We have already discussed the Primary structure of Proteins, which is the polypeptide backbone or amino acid sequence. The amide bonds joining the individual amino acid residues of the backbone have an important role in forming the 3-D structure of proteins. The peptide bond of the amino acid sequence forms a planar structure due to the partial double bond between N and C. This planar structure limits the ways the backbone can fold up and therefore, constrains the shape a folded polypeptide can take.
Figure 5. The Amide Bond showing its partial double bond character and partial charges.
Figure 6. Planes formed on the two sides of an Alpha Carbon and Angles of Rotation of Peptide Bonds.
The degree of rotation of each Peptide Bond unit about the central Alpha-Carbon is limited by the size/shape of the side chain bonded to the Central Carbon. (From Voet/Biochemistry 1990 John Wiley)
©Wilbur H. Campbell, 1995; wcampbel@mtu.edu