Amino acids contain amino (–NH2) and carboxyl (–COOH) functional groups. Depending upon the relative position of amino group with respect to carboxyl group, the amino acids can be classified as α, β, γ, δ and so on. Only α-amino acids are obtained on hydrolysis of proteins. All α-amino acids have trivial names, which usually reflect the property of that compound or its source. Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule. Equal number of amino and carboxyl groups makes it neutral; more number of amino than carboxyl groups makes it basic and more carboxyl groups as compared to amino groups makes it acidic. The amino acids, which can be synthesized in the body, are known as nonessential amino acids. On the other hand, those which cannot be synthesized in the body and must be obtained through diet, are known as essential amino acids.
Match List-I with List-II.
| List-I (Amino acid) | List-II (Side chain, R) |
|---|---|
| (A) Serine | (I) C6H5–CH2– |
| (B) Threonine | (II) HO–CH2– |
| (C) Phenylalanine | (III) (p)HO–C6H4–CH2– |
| (D) Tyrosine | (IV) H3C–CHOH– |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-II, B-IV, C-I, D-III
An α-amino acid has the general formula R–CH(NH2)–COOH, and the amino acids differ only in the side chain, R. Serine and threonine both carry an –OH group in R; phenylalanine and tyrosine both carry a benzene ring.
(A) Serine — This matches (II) HO–CH2–. Its side chain is a CH2 group carrying an –OH group.
(B) Threonine — This matches (IV) H3C–CHOH–. It has one carbon more than serine: the –OH group is on a carbon that also carries a methyl group.
(C) Phenylalanine — This matches (I) C6H5–CH2–, a benzyl group, as the name “phenyl”-alanine suggests.
(D) Tyrosine — This matches (III) (p)HO–C6H4–CH2–. It is the phenylalanine side chain with an –OH group at the para position of the ring.
NCERT (2026-27 edition):
10.2.1 Amino Acids – “…Structures of some commonly occurring amino acids along with their 3-letter and 1-letter symbols are given in Table 10.2.”
Table 10.2: Natural Amino Acids