See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Concept: A chiral centre (stereogenic centre) is a carbon atom bonded to four different substituents. In alpha-amino acids, the alpha-carbon bears an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (-H), and a side chain (R group). For the alpha-carbon to be chiral, all four groups must be different, which requires R ≠ H. Reasoning: Glycine is the simplest amino acid with the side chain R = H. Therefore, its alpha-carbon bears two identical hydrogen atoms (-NH2, -COOH, -H, -H), meaning it has only three distinct substituents. This makes the alpha-carbon achiral (not a chiral centre). Why other options fail: Valine has R = -CH(CH3)2 (isopropyl group), so its alpha-carbon has four different groups and is chiral. Leucine has R = -CH2CH(CH3)2 (isobutyl group), so its alpha-carbon is chiral. Isoleucine has R = -CH(CH3)CH2CH3, so its alpha-carbon is chiral (and it actually has a second chiral centre in the side chain). Thus, glycine is the only amino acid among the options that does not contain a chiral centre. Therefore, the correct answer is C.