Glycine Peptide Molecular Formula: 10 Glycine Condensation Synthesis MCQ Calculation

Introduction

Molecular formulae linear peptide ten glycine condensation synthesis involves linking 10 glycine molecules (C₂H₅O₂N) with loss of water at each peptide bond.

Each condensation removes H₂O (9 bonds for 10 residues), yielding C₂₀H₄₈O₁₈N₁₀ from total C₂₀H₅₀O₂₀N₁₀ minus 9H₂O.

Peptide Formula Calculation

• Single glycine: C₂H₅O₂N (MW 75 Da)
• 10 glycines (unlinked): 10 × C₂H₅O₂N = C₂₀H₅₀O₂₀N₁₀
• Peptide bonds formed: 10 residues → 9 bonds
• Water lost per bond: H₂O (2H + O)
• Total water lost: 9 × H₂O = 9H₁₈O₉
• Final peptide: C₂₀H₅₀₋₁₈O₂₀₋₉N₁₀ = C₂₀H₄₈O₁₈N₁₀

General formula: (n × AA) – (n-1) × H₂O

Detailed MCQ Solution

Question: Molecular formula for linear peptide from ten glycine molecules by condensation?

Option Analysis:

• a. C20H50O20N10 – Formula of 10 free glycines (no bonds formed). Ignores condensation. Incorrect.
• b. C20H48O18N10 – Correct: C₂₀H₅₀O₂₀N₁₀ – 9H₁₈O₉ = C₂₀H₄₈O₁₈N₁₀. Matches 9 peptide bonds. Correct answer.
• c. C20H32O11N10 – Far too few H atoms (32 vs 48). Suggests excessive water loss (~9O missing). Incorrect. [web:21]
• d. C20H50O10N10 – Correct C/N but only 10O (vs 18). Implies loss of 10O atoms, not matching H₂O stoichiometry. Incorrect.

Condensation Synthesis Breakdown

Structure: H₃N⁺-Gly-Gly-…-Gly-COO⁻ (9 -CO-NH- linkages)
Common Peptide Formula Errors