Question

Which of the following is a plasmid?

• A. Both A and C
• B. pBR 322
• C. EcoR I
• D. Hind II

Answer 1

The correct option is B pBR 322

Plasmid
Plasmids are extranuclear, circular, double stranded DNA. They are usually used as vectors in genetic engineering.

pBR322
pBR322 is the most common plasmid vector. It is named after Bolivar and Rodriguez.

Restriction endonuclease
Restriction endonucleases are enzymes which cleave the DNA by digesting phosphodiester bonds at specific sequences (recognition sequence) within the DNA. They help in cutting the vector and the DNA of interest to form rDNA. Examples include Hind II, EcoR I.

Hind II
Hind II is the restriction endonuclease from Haemophilus influenzae with the recognition sequence 5’- GTCGAC -3’.

Eco RI
EcoR I is the restriction endonuclease from Escherichia coli that has 5’- GAATTC -3’ as its recognition sequence.

Final answer
(B) pBR 322