Chemical properties of Amino Acids

Peptide Bond Formation

When two amino acids combine with each other, the amino group of one amino acid combines with carboxyl group of other amino acid. This leads to peptide bond formation. The combination of the amino group of one molecule with the carboxyl group of the other results in the elimination of a water molecule and forms a -CO-NH-bond.

The bond formed above is a peptide bond. The dipeptide contains two amino acids and one peptide bond.

Glycylalanine (Gly-Ala) has structure

The same two amino acids may also form Ala-Gly where the amino group of glycerin may react with the carboxyl group of alamine. Both those dipeptides have 3 free functional groups which further react with relevant groups of other amino acids forming tri, tetra, penta peptides and so on.

Both -CO and -NH groups of peptide bonds are polar. They are involved in hydrogen bond formation. In a protein the amino acids are held together by peptide bonds. The peptides with more than 10 amino acids are called polypeptides. Peptide chains are written with free amino end at left and free carboxyl end at right. Any amino acid sequence is read from N-terminal end to C-terminal end.

Peptide bonds are strong, rigid and planar. They have partial double bond characteristics. They serve as cementing material between individual amino acids. The polypeptide chain is shown below:

The distance between two adjacent a-carbon atoms is 0.36 nm.