Question

Indicate the name and one letter code for the (proteinogenic) amino acid best fitting the given description

1. Of the amino acids with an amide functional group in its sidechain, the one with the shortest sidechain

 

2. The amino acid that has an amino group in its sidechain;  in some proteins, it is post-translationally hydroxylated via a Vitamin C dependent enzyme

3. The amino acid with an aromatic (but not heterocyclic) sidechain that is nonetheless capable of hydrogen bonding and is often found in the edge of membrane spanning helices and is also capable of being post-translationally modified by ATP-dependent phosphorylation

4. The amino acid having a sidechain including an imidazole ring with a pKa near physiological pH

 

5. Of the proteinogenic amino acids with branched sidechains (the “branched chain amino acids”), the one with the shortest sidechain

 

6. Of the amino acids with a carboxylate group in the sidechain, the one with the longest sidechain

 

7. Of the amino acids, the one which is achiral (and hence forms peptides with the largest allowable regions in its Ramachandran plot)

Answer 1

Single letter codes are given in brackets after the name.

a) There are two amino acids with amide side chains. Glutamine, with a side chain of 3 carbons, and Asparagine, with a side chain of 2 carbons.

Hence, the smaller one is Asparagine (N)

b) Two amino acids undergo hydroxylation involving Vitamin C; these are Proline and Lysine.

Out of these, one having an amino group inside the chain is Lysine (K)

c) Only aromatic amino acid containing -OH group is Tyrosine (Y)

d) Amino acid-containing imidazole ring is Histidine (H)

e) Branched-chain amino acids are Valine, Leucine, and Isoleucine. Both leucine and isoleucine are of 3 carbon side chain while Valine has 2 carbon chain.

So, the answer is Valine (V)

f) Carboxylate side chains are in Aspartic acid, with 2 carbons, and Glutamic acid, with 3 carbons.

So, the longer one is Glutamic acid (E)

g) Only achiral proteogenic amino acid is Glycine (G).