A plasmid of 12 kb is isolated and its concentration is 300 µg ml⁻¹. How many plasmid copies are present in 2 ml of this preparation? (Use 1 bp = 660 Da and Avogadro's number = 6.022×10²³ mol⁻¹.)

easy 3 marks Class 12 · Biology · Biotechnology and Its Applications

Answer

4.56×10¹³ copies

The correct answer is 4.56×10¹³ copies — Multiply by the volume (2 ml) to obtain total copies: 2.28×10¹³ copies ml⁻¹ × 2 ml ≈ 4.56×10¹³ copies.

Step-by-step solution

Calculate the molecular weight of the plasmid: 12 000 bp × 660 Da = 7.92×10⁶ Da.
Convert concentration to grams per millilitre: 300 µg ml⁻¹ = 300×10⁻⁶ g ml⁻¹.
Determine the number of moles per millilitre: (300×10⁻⁶ g)/(7.92×10⁶ g mol⁻¹) ≈ 3.7879×10⁻¹¹ mol ml⁻¹.
Convert moles to copies per millilitre: 3.7879×10⁻¹¹ mol ml⁻¹ × 6.022×10²³ copies mol⁻¹ ≈ 2.28×10¹³ copies ml⁻¹.
Multiply by the volume (2 ml) to obtain total copies: 2.28×10¹³ copies ml⁻¹ × 2 ml ≈ 4.56×10¹³ copies.

Common mistake: Using base pair weight of 650 Da instead of 660 Da

Concept tested: Plasmid copy number calculation