Two amino acids with negatively charged side chains are
Two amino acids with negatively charged side chains are
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Correct Answer: Option A
Explanation
Amino acids with negatively charged side chains (acidic amino acids, pKa of side chain ~2–4, so deprotonated and negatively charged at physiological pH 7.4): Aspartate (Asp, D) — side chain:, pKa = 3.65. Glutamate (Glu, E) — side chain:, pKa = 4.25. Both carry a netcharge at pH 7.4. In contrast: Glycine has no ionisable side chain; Lysine (pKa ~10.5) and Arginine (pKa ~12.5) are positively charged. These acidic amino acids are critical for enzyme active sites (Asp in the catalytic triad of serine proteases; Glu in lysozyme), metal-binding (Cacoordination), and signal transduction.