Question

The general structure of alpha amino acid can be represented as

. Which amino acid is not correctly matched with R-given?

• A. R = -CH\(_2\)-C\(_6\)H\(_4\)-OH(p) - (Tyrosine)
• B. R = -CH\(_2\)-SH - (Cysteine)
• C. R = -CH\(_2\)-CH\(_2\)-S-CH\(_3\) - (Serine)
• D.

  

Hint:

It is very helpful to memorize the structures of the 20 common amino acids, especially by classifying them into groups: nonpolar, polar, acidic, and basic. Key ones to remember: - Glycine (R=H) - Alanine (R=CH\(_3\)) - Serine (R=CH\(_2\)OH) - Cysteine (R=CH\(_2\)SH) - Aspartic Acid (R=CH\(_2\)COOH) - Lysine (R=(CH\(_2\))\( _4 \)NH\(_2\))

Answer 1

The Correct Option is C

We need to check if the given R group (side chain) corresponds to the named amino acid.
(A) Tyrosine (Tyr, Y): Its side chain is a p-hydroxybenzyl group. The formula is -CH\(_2\)-C\(_6\)H\(_4\)-OH. This match is correct.
(B) Cysteine (Cys, C): Its side chain contains a thiol group. The formula is -CH\(_2\)-SH. This match is correct.
(C) Serine (Ser, S): Its side chain is a hydroxymethyl group. The formula is -CH\(_2\)-OH. The R group given is -CH\(_2\)-CH\(_2\)-S-CH\(_3\). This R group actually belongs to Methionine (Met, M). Therefore, the match with Serine is incorrect.
(D) Asparagine (Asn, N): Its side chain is the amide derivative of aspartic acid. The formula is -CH\(_2\)-C(=O)-NH\(_2\). This match is correct.
The incorrectly matched pair is (C).