Question

The correct structure of dipeptide, Gly-Ala (glycyl alanine) is:

• A. \(\text{H}_2\text{NCH}_2\text{CONHCH(CH}_3\text{)COOH}\)
• B. \(\text{HOOC} - \text{CH}_2 - \text{NH} - \text{CO} - \text{CH(CH}_3\text{)} - \text{NH}_2\)
• C. \(\text{HOOC} - \text{CH(CH}_3\text{)} - \text{NH} - \text{CO} - \text{CH}_2 - \text{NH}_2\)
• D. \(\text{H}_2\text{N} - \text{CH(CH}_3\text{)} - \text{CO} - \text{NH} - \text{CH}_2 - \text{COOH}\)

Answer 1

The Correct Option is A

To determine the correct structure of the dipeptide Gly-Ala (glycyl alanine), we need to understand how amino acids link together to form peptides.

Glycine (Gly): H₂NCH₂COOH

Alanine (Ala): H₂NCH(CH₃)COOH

A dipeptide is formed by the condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH₂) of another amino acid, with the elimination of a water molecule (H₂O). The bond formed is a peptide bond (-CONH-).

In Gly-Ala, glycine is the first amino acid, and alanine is the second amino acid. Therefore, the carboxyl group of glycine will react with the amino group of alanine.

Let's analyze each option:

• Option 1: H₂NCH₂CONHCH(CH₃)COOH: This structure shows the carboxyl group of glycine (-CH₂COOH) reacting with the amino group of alanine (-NHCH(CH₃)-), forming a peptide bond (-CONH-). This is the correct structure.
• Option 2: HOOC−CH₂−NH−CO−CH(CH₃)−NH₂: This structure is incorrect because the peptide bond is formed in the wrong orientation.
• Option 3: HOOC−CH(CH₃)−NH−CO−CH₂−NH₂: This structure represents Ala-Gly, not Gly-Ala.
• Option 4: H₂N−CH(CH₃)−CO−NH−CH₂−COOH: This structure also represents Ala-Gly, not Gly-Ala.

Therefore, the correct structure of Gly-Ala is:

Option 1: H₂NCH₂CONHCH(CH₃)COOH