Question 27:

Read the following statements carefully:

(A) DNA ligases are enzymes that create a phosphodiester bond between DNA fragments.
(B) A protein containing one or more prosthetic groups is called a conjugated protein.
(C) A type of enzyme inhibition reversed by increasing the substrate concentration is called competitive inhibition.
(D) Two stereoisomers of a given sugar that differ only in the configuration about carbonyl carbon atom are called anomers.

Choose the correct answer from the options given below:

(A) (A), (B) and (C) only
(B) (A), (B) and (D) only
(C) (A), (C) and (D) only
(D) (B), (C) and (D) only

DNA ligase, conjugated proteins, competitive inhibition, and anomers are core biochemistry concepts, but one statement here is incorrect. The correct answer is (B) (A), (B) and (D) only.

Correct Answer

Option (B) (A), (B) and (D) only is correct. Statements (A), (B), and (D) accurately define their terms, while (C) is false because competitive inhibition is overcome by excess substrate, but the description fits non-competitive inhibition where Vmax decreases without affecting Km.

Statement Explanations

• (A) Correct: DNA ligases seal nicks in DNA by catalyzing phosphodiester bond formation between 3′-OH and 5′-phosphate ends of adjacent fragments, essential for replication and repair.

• (B) Correct: Conjugated proteins have non-amino acid prosthetic groups (e.g., heme in hemoglobin) covalently or non-covalently bound, enabling functions like oxygen transport.​

• (C) Incorrect: Competitive inhibition involves inhibitor competing with substrate for the active site; it is reversed by high substrate (increases Km, Vmax unchanged). The statement describes non-competitive inhibition.​

• (D) Correct: Anomers are stereoisomers (α and β) of sugars differing only at the anomeric carbon (former carbonyl), as in glucose where OH orientation at C1 varies.​

Options Comparison