# DBT JRF 2022 — Question 8

Exam: DBT JRF 2022 · Section: B · Topic: Molecular Biology › Nucleases & Nucleic Acid Enzymology · Difficulty: Medium

## Question

Which enzyme will digest RNA in a DNA-RNA Hybrid?

## Options

- **A.** RNase A
- **B.** BamHI
- **C.** Reverse transcriptase
- **D.** RNAse H

## Answer

Option D

## Explanation

RNase H: enzyme that digests RNA in a DNA:RNA hybrid: RNase H (Ribonuclease H) is an endonuclease with specific activity against the RNA strand of an RNA:DNA heteroduplex: • It cleaves the RNA strand internally (5'→3' and 3'→5') but does NOT degrade single-stranded RNA or double-stranded DNA. • Biological roles: During reverse transcription (retroviruses, retrotransposons), after first-strand cDNA is made, the RNA template must be removed so that second-strand synthesis can occur — RNase H does this. • Also functions during DNA replication to remove RNA primers (e.g., Okazaki fragment primers) in some organisms. Distractors: • RNase A: degrades single-stranded RNA, not RNA:DNA hybrids. • BamHI: a DNA restriction endonuclease. • Reverse transcriptase: has intrinsic RNase H activity but IS reverse transcriptase, not a standalone nuclease. Answer: RNase H (Option 4).

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