# DBT JRF 2020 — Question 50

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Hard

## Question

The $\beta$ -sheet rich structure of prion protein represents the

## Options

- **A.** intermediator state of the protein
- **B.** normal functional protein
- **C.** abnormal disease-causing protein
- **D.** soluble form of the protein

## Answer

Option C

## Explanation

DNase I (bovine pancreatic deoxyribonuclease I) is an endonuclease that makes single-stranded nicks in double-stranded DNA, but it also cleaves single-stranded DNA and RNA:DNA hybrids. The correct statement is that DNase I acts on BOTH single-stranded and double-stranded DNA — it does NOT cleave ONLY double-stranded DNA. The incorrect pair is therefore 'DNase I: Cleaves only double stranded DNA.' In contrast: Alkaline phosphatase correctly removes 5'-phosphates from DNA/RNA ends; DNA Pol I nick translation correctly: Pol I uses its 5'→3' exonuclease to remove the downstream fragment while its polymerase simultaneously synthesises replacement DNA in 5'→3' direction; RNA polymerase correctly performs transcription.

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