# DBT JRF 2022 — Question 43

Exam: DBT JRF 2022 · Section: A · Topic: Molecular Biology › DNA Structure & Physical Properties · Difficulty: Medium

## Question

What will be the length of a DNA molecule containing 10 million bp?

## Options

- **A.** 340 mm
- **B.** 34 mm
- **C.** 3.4 mm
- **D.** 0.34 mm

## Answer

Option C

## Explanation

Length of a DNA molecule with 10 million base pairs: Key fact: In B-form DNA, the rise per base pair = 0.34 nm (the distance along the helical axis per bp). $\text{Length} = \text{No. of bp} \times 0.34\,\text{nm/bp}$ $= 10 \times 10^6\,\text{bp} \times 0.34\,\text{nm/bp}$ $= 3.4 \times 10^6\,\text{nm}$ $= 3.4 \times 10^6 \times 10^{-9}\,\text{m} = 3.4 \times 10^{-3}\,\text{m} = 3.4\,\text{mm}$ For context: The human genome has ~3.2 billion bp → ~1 metre of DNA per cell. Answer: 3.4 mm (Option 3).

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