Among the following L-serine is a) H₂N-C(=NH)-NH-CH₂-CH₂-CH₂-CH(NH₂)-COOH (guanidino side chain) b) (imidazol-

Choose the Best Answer · Q15

Q. Among the following L-serine is

a) H₂N-C(=NH)-NH-CH₂-CH₂-CH₂-CH(NH₂)-COOH (guanidino side chain)

b) (imidazol-4-yl)-CH₂-CH(NH₂)-COOH (five-membered N-containing ring side chain)

c) HO-CH₂-CH(NH₂)-COOH

d) CH₃-CH(OH)-CH(NH₂)-COOH [Textbook note: the four options are printed as skeletal structural formulae of amino acids; the condensed formula given above for each option faithfully represents the drawn structure.]

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Step 1. Serine is one of the twenty standard amino acids, with the simple structural formula HOCH₂-CH(NH₂)-COOH -- an α-carbon bearing NH₂, COOH, H, and a short -CH₂OH side chain carrying the single defining hydroxyl group.

Step 2. Match each drawn option against known amino-acid side chains. Option (a), with a guanidino group (-NH-C(=NH)-NH₂) at the end of a propyl chain, is the side chain of arginine, not serine. Option (b), with a five-membered ring containing two nitrogens (an imidazole ring) attached via a -CH₂- linker, is the side chain of histidine, not serine. Option (d), with both a branched -OH and a -CH₃ group on the carbon adjace …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2022Set ANNUAL1 markMCQ
$Q. Which of the following amino acids are achiral ?$
(a) Proline
(b) Alanine
(c) Glycine
(d) Leucine
›Reveal solutionSolution

Chirality at the $\alpha$ -carbon requires four different substituents; glycine's $\alpha$ -carbon carries $-NH_2$ , $-COOH$ , and two identical $-H$ atoms, so it fails this test and glycine is achiral, unlike proline, alanine, and leucine.

…

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CBSE 2018Set ANNUAL1 markMCQ
$Q. The amino acid without chiral carbon is :$
(a) proline
(b) glycine
(c) thyrosine
(d) alanine
›Reveal solutionSolution

A chiral carbon must carry four different groups. In glycine, the α-carbon bears two identical H atoms, so it is not chiral.

All standard amino acids have the general structure $H_2N-CH(R)-COOH$ , where the α-carbon is bonded to an $-NH_2$ group, a $-COOH$ group, an H atom, and the side chain R. For the α-carbon to be a chiral (asymmetric) centre, all four substituents attached to it must be different.

…

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CBSE 2017Set ANNUAL1 markMCQ
$Q. The building block of proteins are :$
(a) $\alpha$ -hydroxy acid
(b) $\alpha$ -amino acid
(c) $\beta$ -hydroxy acid
(d) $\beta$ -amino acid
›Reveal solutionSolution

The 20 or so standard amino acids that make up proteins are all $\alpha$ -amino acids, i.e. the amino group is on the carbon adjacent to the carboxyl group.

In an $\alpha$ -amino acid, the $-NH_2$ group is attached to the $\alpha$ -carbon (the carbon directly bonded to $-COOH$ ); these units condense via peptide ( $-CONH-$ ) bonds to form the polypeptide chains of proteins. $\beta$ -amino acids and $\alpha$ / $\beta$ -hydroxy acids are real classes o …

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Q.Among the following L-serine is

Concept understanding — Amino Acids and Their Classification

Q.Among the following L-serine is

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