Question

Match LIST-I with LIST-II

Choose the correct answer from the options given below:

• A. A-I, B-II, C - III, D- IV
• B. A-I, B - III, C - II, D - IV
• C. A-I, B-II, C - IV, D - III
• D. A-III, B - IV, C - I, D - II

Hint:

Associate keywords: \textbf{Mismatch} \(\rightarrow\) Methylation (\textbf{Dam methylase}). \textbf{Base} Excision \(\rightarrow\) AP site (\textbf{AP endonuclease}). \textbf{Nucleotide} Excision \(\rightarrow\) Bulky lesion (\textbf{ABC excinuclease}). \textbf{Direct} Repair \(\rightarrow\) Light/UV (\textbf{Photolyase}).

Answer 1

The Correct Option is B

Step 1: Concept Overview:
The question requires linking E. coli DNA repair pathways to their characteristic enzymes or proteins.
Step 2: Detailed Solution:
Matching each repair system with its key enzyme:


A. Mismatch repair (MMR): This system fixes replication errors. E. coli MMR uses methylation to distinguish the new (error-containing) strand from the old template. Dam methylase methylates adenine in GATC sequences. New strands are temporarily unmethylated, allowing error identification and correction. Dam methylase provides system specificity. This corresponds to I.

B. Base-excision repair (BER): This pathway removes single damaged bases. A DNA glycosylase removes the base, creating an AP site. An AP endonuclease then cleaves the DNA backbone at this site for repair. This corresponds to III.

C. Nucleotide-excision repair (NER): This pathway removes bulky lesions. The key E. coli enzyme is UvrABC, also known as ABC excinuclease. It identifies the lesion and cuts on either side. This corresponds to II.

D. Direct repair: This directly reverses damage. An example is DNA photolyases repairing UV-induced pyrimidine dimers using visible light. This corresponds to IV.

Step 3: Final Answer:
The correct matches are A-I, B-III, C-II, D-IV.