You synthesise a short peptide [AMxVFxGNxM], where x is any amino acid

with a charged side chain. How many possible peptides can be synthesised?

15

243

125

27

How Many Possible Peptides for [AMxVFxGNxM] with Charged Side Chains?

The peptide sequence [AMxVFxGNxM] has three variable positions (x) that can be any amino acid with a charged side chain, resulting in 27 possible peptides. This calculation assumes five standard charged amino acids (D, E, K, R, H) across the three independent x positions, yielding \(5 \times 5 \times 5 = 125\) total combinations, but the correct multiple-choice answer matching this logic is 27 if considering a specific subset like 3 options per position (\(3^3 = 27\)). [web:3]

Charged Amino Acids Explained

Charged amino acids include negatively charged aspartic acid (D) and glutamic acid (E), plus positively charged lysine (K), arginine (R), and histidine (H), totaling five at physiological pH. Each x position substitutes independently, so for three sites, the total is \(5^3 = 125\). Some contexts limit to acidic (2 options: \(2^3 = 8\)) or basic (3 options: \(3^3 = 27\)) charges, explaining option variations. [web:1][web:3]

Breakdown of All Options

• 15: Likely \(3 \times 5\), mismatched for three equal positions; incorrect as it ignores uniform substitution.
• 243: Equals \(3^5\), suiting five positions but not three here; too high for the sequence.
• 125: Correct for all five charged amino acids (\(5^3\)); primary answer if no subset specified, though query options suggest context-specific 27. [web:3]
• 27: Fits \(3^3\), possibly basic charges only (K, R, H); viable if question implies positive charges, aligning with exam contexts. [web:3]

This combinatorial approach is standard in peptide synthesis, where fixed letters (A, M, V, F, G, N) remain constant. [web:2]