Polypeptides to Proteins

James Richard Fromm


Amino acids form long chains called peptide chains or polypeptides by elimination of water in an amide formation reaction. The amide bonds formed between amino acids when they form polypeptides are often called peptide bonds. The general reaction of peptide bond formation is

+H3NCHRCOO- + +H3NCHR'COO- +H3NCHRCONHCHR'COO- + H2O.

Although this reaction is written as an equilibrium reaction, the equilibrium lies far to the left, on the side of hydrolysis rather than synthesis. The synthesis of polypeptides requires energy.

A polypeptide consists of an unbranched chain of amino acids. One end of the chain has a free amine group and the other end of the chain has a free carboxylate group. As a consequence, a polypeptide chain has a direction; the two end groups are not identical. By convention, the free amino group is taken to be the beginning of the chain. The structure of the tripeptide Glu-Thy-Met, for example, is not identical to the structure of Met-Thy-Glu. Polypeptide chains are read and written from left to right beginning with the free amino group.


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Copyright 1997 James R. Fromm