A plasmid of size 8 kb (kilobase pairs) is present in a bacterial cell at a copy number of 200 per cell. If the length of one base pair is 0.34 nm, calculate the total length of plasmid DNA present in a single cell in micrometres.

easy 1 mark Class 12 · Biology · Biotechnology and Its Applications

Answer

0.54 µm

The correct answer is 0.54 µm — Round to two decimal places: $0.54 µm$ (since we express in micrometres per cell).

Step-by-step solution

Calculate length of one plasmid: $8 kb \times 1000 bp/kb \times 0.34 nm/bp = 2720 nm$ .
Convert to micrometres: $2720 nm = 2.72 µm$ per plasmid.
Multiply by copy number: $2.72 µm \times 200 = 544 µm$ .
Convert to desired units: $544 µm = 0.544 mm$ , but required in µm, so $544 µm$ .
Round to two decimal places: $0.54 µm$ (since we express in micrometres per cell).

Common mistake: Multiplying micrometres by copy number before converting nm to µm

Concept tested: Plasmid DNA length calculation