Match the amino acid (AA) with its right side chain category:

1) methionine A) negatively charged polar AA

2) histidine B) nonpolar aromatic AA

3) alanine C) positively charged polar AA

4) threonine D) nonpolar AA

5) tryptophan E) polar AA

6) aspartic acid F) nonpolar aliphatic AA

1) methionine ⇒ D) nonpolar AA

2) histidine ⇒ C) positively charged polar AA

3) alanine ⇒ F) nonpolar aliphatic AA

4) threonine ⇒ E) polar AA

5) tryptophan ⇒ B) nonpolar aromatic AA

6) aspartic acid ⇒ A) negatively charged polar AA

Explanation:

Methionine (Met) contains a S-methyl thioether side chan, which confers to the molecule a nonpolar character.

Histidine (His) has an imidazole group wich is partially protonated so it is a positively charged polar amino acid.

The side chain group of alanine (Ala) is a methyl group (-CH₃) so it is considered the most simple aliphatic AA.

Threonine (Thr) contains an hydroxyl group so it is a polar amino acid.

Tryptophan (Trp) is one of the three aromatic amino acids in the nature (along with phenylalanine and tyrosine) and contains an indole side chain.

Aspartic acid (Asp) has an acidic side chain (CH₂COOH) which is desprotonated at physiological pH so it is negatively charged.