Question

The structure of Gly-Ala (Glycylalanine) is:

• A.
• B.
• C.
• D.

Hint:

Key points about dipeptides: 1. Always drawn with N-terminus (NH$_2$) on left
2. Peptide bonds are rigid and planar
3. R-groups alternate above/below the peptide chain
4. Named from N-terminal to C-terminal residue

Answer 1

The Correct Option is B

Gly-Ala (Glycylalanine) is a dipeptide composed of: - Glycine (Gly) as the N-terminal amino acid.
- Alanine (Ala) as the C-terminal amino acid. Correct structural features: - Free amino group (-NH$_2$) at the N-terminus.
- Free carboxyl group (-COOH) at the C-terminus.
- Peptide bond (-CO-NH-) linking the two amino acids.
- Methyl side chain (-CH$_3$) from alanine. Analysis of options: - Option 1: Shows two separate amino acids (Gly + Ala), not a dipeptide.
- Option 2: Correct dipeptide structure with proper peptide bond.
- Option 3: Incorrect hydroxyl group (OH) at N-terminus.
- Option 4: Shows ester linkage (-CO-O-) instead of peptide bond. 
Thus, the correct answer is (2).

Answer 2

Glycylalanine is a dipeptide formed from two amino acids:

• Glycine (Gly): NH₂–CH₂–COOH
• Alanine (Ala): NH₂–CH(CH₃)–COOH

When these two amino acids undergo a condensation reaction, the carboxyl group of glycine reacts with the amino group of alanine, releasing a water molecule and forming a peptide bond (–CO–NH–). 

Resulting Dipeptide Structure (Gly-Ala):
H₂N–CH₂–CO–NH–CH(CH₃)–COOH
The image shown above correctly represents the structure of Glycylalanine, featuring:

• A terminal amino group from glycine (left side)
• A peptide linkage between glycine and alanine
• A terminal carboxylic acid group from alanine (right side)

Final Answer:
The given structure is Gly-Ala (Glycylalanine)