See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Concept: Acidic groups are functional groups that can donate a proton (H+). The most common acidic groups in amino acids are carboxylic acid groups (-COOH) and the conjugate acid of the amino group (-NH3+). Step 1: Identify the structure. This amino acid is shown in its zwitterionic/partially ionized form. The molecule is glutamic acid (or a related structure) displayed as: NH3(+)-CH(CO2(-))-CH2-CH2-CO2H. Step 2: Identify all potentially acidic groups in the parent (un-ionized) amino acid: - The alpha-carboxyl group: shown here as CO2(-) (already deprotonated in this representation, but it is an acidic group -COOH in neutral form). - The side-chain carboxyl group: shown as CO2H (terminal -COOH), which is an acidic group. - The alpha-amino group: shown as NH3(+), which is also acidic (can donate a proton to give NH2), but in standard classification for amino acid acidic groups, the question focuses on -COOH type groups. Step 3: Count acidic groups. In the context of this question, the two carboxylic acid groups (alpha-COOH and the side-chain -COOH) are counted as the acidic groups. Both CO2(-) and CO2H represent carboxylate/carboxylic acid groups — there are 2 such groups total. Step 4: The NH3(+) group is the acidic group of the ammonium type, but in the typical classification used here, the question counts carboxylic acid (-COOH) groups as the acidic groups, giving a total of 2. Why not 1 or 3: There is only 1 terminal -CO2H visible, but the alpha -CO2(-) is also a carboxylic acid group (deprotonated form), so both count. That gives 2, not 1. Including NH3+ would give 3, but the standard answer counts only the carboxylic acid-type acidic groups. Therefore, the correct answer is 2.