Peptide Bond Formaion or Amide Synthesis:
The formation of peptides is nothing more than the application
of the amide synthesis reaction. By convention, the amide
bond in the peptides should be made in the order that the amino
acids are written. The amine end (N terminal) of an amino acid
is always on the left, while the acid end (C terminal) is on
The reaction of glycine with alanine to form the dipeptide
glyclalanine is written as shown in the graphic on the left.
Oxygen (red) from the acid and hydrogens (red) on the amine form
a water molecule. The carboxyl oxygen (green) and the amine nitrogen
(green) join to form the amide bond.
If the order of listing the amino acids is reversed, a different
dipeptide is formed such as alaninylglycine.
QUES. Write the reactions for:
a) ala + gly ---> Answer
b) phe + ser ----> Answer
Salt Formation Contrast:
The salt formation reaction
is simply the transfer of the -H (positive ion) from the acid
to the amine and the attraction of the positive and negative
chagres. The acid group becomes negative, and the amine nitrogen
becomes positive because of the positive hydrogen ion.
No water is formed and there is only one product, the salt.