Question

If the carboxylic acid group of glycine and amino acid group of alanine undergo elimination of a water molecule, the name of the compound thus formed is

• A. alanylglycide (dipeptide)
• B. glycylalanide (tripeptide)
• C. glycylalanine (dipeptide)
• D. alanylglycine (dipeptide)

Answer 1

The correct option is C glycylalanine (dipeptide)

The amino acid unit having free $-N{H}_2$ groups is called N-terminal end whereas, the amino acid unit with free​ $-COOH$ group is called C-terminal end.​
The structure is written with​ N-terminal end to the left and​ C-terminal end to the right.
At N-terminal or C-terminal further bond​ formation takes place and tri, tetra,​ pentapeptides are formed.​

Naming of Polypeptides
1. Starts from –N–terminal residue.
Suffix -ine of amino acids is ​replaced by -yl for all except ​
amino acid of C-terminal residue.
Example: Glycine $\stackrel{}{\to }$ Glycyl​
Alanine $\stackrel{}{\to }$ Alanyl​
Lysine $\stackrel{}{\to }$ Lysyl​
Alanylglycylphenylalanine means Ala-Gly-Phe or​ A-G-F.​

If the carboxyl acid group of glycine and amino group of alanine undergo elimination of a water molecule, the formed compound is glycylalanine (dipeptide).
Hence, (c) is correct.