Question

Put the following steps of the Mismatch Repair Mechanism in order:

I. DNA Ligase repairs the DNA backbone.
II. Exonuclease removes the misplaced nucleotide.
III. DNA Polymerase adds the correct nucleotide.
IV. The mismatched DNA is marked with a cut.

(A) IV, I, II, III
(B) I, IV, II, III
(C) IV, II, III, I
(D) I, II, III, IV

Answer 1

The correct order of the steps for the mismatch repair mechanism is: IV, II, III, I, which corresponds to the mismatched DNA being marked, the removal of the incorrect nucleotide by exonuclease, the addition of the correct nucleotide by DNA polymerase, and the repair of the DNA backbone by DNA ligase.(C) IV, II, III, I

Step-by-step explanation:

The correct order of steps in the mismatch repair mechanism is option (C) IV, II, III, I. Here is the step-by-step explanation:

1. The mismatched DNA is marked with a cut. This is done by enzymes such as MutH in E. coli which recognizes the non-methylated, newly synthesized DNA strand.
2. Exonuclease removes the misplaced nucleotide along with some surrounding nucleotides. The enzyme excises a portion of the DNA strand including the incorrect nucleotide.
3. DNA Polymerase then adds the correct nucleotide(s) by filling in the gap where the incorrect nucleotides were removed.
4. Finally, DNA Ligase repairs the DNA backbone by sealing the remaining nick with a phosphodiester bond, restoring the integrity of the DNA molecule.

The mismatch repair mechanism is crucial for correcting errors that escape the proofreading activity of DNA polymerase during DNA replication. It directly impacts the fidelity of DNA synthesis and the prevention of mutations.

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