Proteins and polypeptides are formed by the condensation of α-amino acids. The correct representation of the dipeptide, glycyl alanine is

A
$H_{2} N - {CH}_{2} - CO - NH - CH ({CH}_{3}) - COOH$
B
$H_{2} N - CH ({CH}_{3}) - CO - NH - {CH}_{2} - COOH$
C
$HOOC - {CH}_{2} - NH - CO - CH ({CH}_{3}) - {NH}_{2}$
D
$HOOC - CH ({CH}_{3}) - NH - CO - {CH}_{2} - {NH}_{2}$

Solution:

Proteins, polypeptides, oligopeptides are written from N-terminal to C-terminal of amino acid residues.

$∴$ Glycyl alanine means

-COOH group of glycine must condense with $- {NH}_{2}$ group of alanine so that the $- {NH}_{2}$ group of glycine will be free and it will be present on left hand terminal.

$\underset{Glycine}{H_{2} N - {CH}_{2} - COOH} + \underset{Alanine}{H_{2} N - \underset{\overset{|}{{CH}_{3}}}{CH} - COOH} \overset{H_{2} O}{\to} \underset{Glycyl alanine}{H_{2} N - {CH}_{2} - \overset{\underset{∥}{O}}{C} - NH - \underset{\overset{|}{{CH}_{3}}}{CH} - COOH}$

Solution:

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