# DBT JRF 2020 — Question 61

Exam: DBT JRF 2020 · Section: B · Topic: Molecular Biology · Difficulty: Medium

## Question

Which of the following is NOT a feature of bacterial DNA replication?

## Options

- **A.** semi-discontinuous
- **B.** chain growth in the 5' $\rightarrow$ 3' direction
- **C.** semi-conservative
- **D.** unidirectional

## Answer

Option D

## Explanation

Restriction mapping with double digests: BamHI alone: 2 kb + 3 kb (1 cut site → 2 fragments). HindIII alone: 0.7 kb + 0.8 kb + 3.5 kb (2 cut sites → 3 fragments). BamHI + HindIII double digest: 0.7 kb + 0.8 kb + 1.3 kb + 2.2 kb (3 cut sites → 4 fragments). Analysis: The 0.7 and 0.8 kb fragments appear in both HindIII single and double digests → both HindIII sites are in the same BamHI fragment. The 3.5 kb HindIII fragment is cut by BamHI into 1.3 + 2.2 kb (1.3+2.2=3.5 ✓). Total linear DNA: 2+3=5 kb; 0.7+0.8+3.5=5 kb; 0.7+0.8+1.3+2.2=5 kb ✓. Map: |---0.7---|---0.8---|---1.3---|---2.2---| with HindIII at positions 0.7 and 1.5, BamHI at position 2.3 (i.e. one BamHI between two HindIII sites).

Source: https://mypyqbuddy.com/questions/which-of-the-following-is-not-a-feature-6a05a8a02adafec470293255