Which among the following amino acids has a lowest molecular mass?

Which among the following amino acids has a lowest molecular mass?
  1. Proline
  2. Aspartic acid
  3. Serine
  4. Glycine

Solution

Steps to Calculate Molecular Mass: - Atomic Masses: - Hydrogen (H): $\mathbf{1} \mathbf{g} / \mathrm{mol}$ - Carbon (C): $\mathbf{1 2} \mathbf{~ g} / \mathrm{mol}$ - Nitrogen (N): $\mathbf{1 4} \mathbf{~ g} / \mathrm{mol}$ - Oxygen (0): $16 \mathrm{~g} / \mathrm{mol}$ 1. Glycine $\left(\mathrm{NH}_2-\mathrm{CH}_2-\mathrm{COOH}\right)$ - Molecular formula: $\mathrm{C}_2 \mathrm{H}_5 \mathrm{NO}_2$ - Calculation: $(2 \times 12)+(5 \times 1)+(1 \times 14)+(2 \times 16)=24+5+14+32=75 \mathrm{~g} / \mathrm{mol}$ 2. Serine $\left(\mathrm{NH}_2-\mathrm{CH}(\mathrm{OH})-\mathrm{CH}_2-\mathrm{COOH}\right)$ - Molecular formula: $\mathrm{C}_3 \mathrm{H}_7 \mathrm{NO}_3$ - Calculation: $(3 \times 12)+(7 \times 1)+(1 \times 14)+(3 \times 16)=36+7+14+48=105 \mathrm{~g} / \mathrm{mol}$ 3. Proline $\left(\mathrm{NH}_2-\mathrm{CH}\left(\mathrm{CH}_2\right)_3-\mathrm{COOH}\right)$ - Molecular formula: $\mathrm{C}_5 \mathrm{H}_9 \mathrm{NO}_2$ - Calculation: $(5 \times 12)+(9 \times 1)+(1 \times 14)+(2 \times 16)=60+9+14+32=115 \mathrm{~g} / \mathrm{mol}$ 4. Aspartic Acid ( $\left.\mathrm{NH}_2-\mathrm{CH}\left(\mathrm{CH}_2-\mathrm{COOH}\right)-\mathrm{COOH}\right)$ - Molecular formula: $\mathrm{C}_4 \mathrm{H}_7 \mathrm{NO}_4$ - Calculation: $(4 \times 12)+(7 \times 1)+(1 \times 14)+(4 \times 16)=48+7+14+64=133 \mathrm{~g} / \mathrm{mol}$ Conclusion: - By solving, the molecular masses are: - Glycine: $75 \mathrm{~g} / \mathrm{mol}$ - Serine: $105 \mathrm{~g} / \mathrm{mol}$ - Proline: $115 \mathrm{~g} / \mathrm{mol}$ - Aspartic Acid: $133 \mathrm{~g} / \mathrm{mol}$ Thus, Glycine has the lowest molecular mass.

Asked in: MHT CET 2020 (19 Oct Shift 1)

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