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

The structure of a dipeptide, such as Gly-Ala (glycyl alanine), involves the peptide bond formation between two amino acids. The first amino acid in this dipeptide is glycine (Gly), which has the formula \(\text{NH}_2\text{CH}_2\text{COOH}\), and the second amino acid is alanine (Ala), with the formula \(\text{NH}_2\text{CH(CH}_3\text{)COOH}\). In a dipeptide formation, the carboxyl group \(-\text{COOH}\) of the first amino acid reacts with the amino group \(-\text{NH}_2\) of the second, resulting in the release of a water molecule and the formation of a peptide bond \(\text{-CONH-}\).

Steps to construct Gly-Ala: 

1. Identify the N-terminus (beginning) of the dipeptide: The N-terminus of Gly-Ala is derived from glycine, \(\text{NH}_2\text{CH}_2\text{-}\).
2. Attach the peptide bond: Form the peptide bond \(\text{-CONH-}\) from the carboxyl group of glycine and the amino group of alanine.
3. Add the alanine structure following the peptide bond: Append the structure \(\text{CH(CH}_3\text{)COOH}\), representing alanine, to complete the dipeptide.

By following these steps, the complete structure for the dipeptide Gly-Ala is: \(\text{H}_2\text{NCH}_2\text{CONHCH(CH}_3\text{)COOH}\)

This structure is the correct representation of glycyl alanine, with the N-terminus having an amino group from glycine and the C-terminus ending with a carboxylic acid group from alanine.

Answer 2

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