Question

Which of these enzymes is required to cleave a plasmid?

• A. Ligase
• B. Endonuclease
• C. Exonuclease
• D. Polymerase

Hint:

Restriction enzymes are indispensable tools in molecular biology.

Answer 1

The Correct Option is B

The enzyme required to cleave a plasmid is Endonuclease.

(A) Ligase - Incorrect: DNA ligase joins DNA fragments, it doesn't cut them.

(B) Endonuclease - Correct: Restriction endonucleases (like EcoRI) cut plasmid DNA at specific recognition sites.

(C) Exonuclease - Incorrect: These remove nucleotides from DNA ends, not make internal cuts.

(D) Polymerase - Incorrect: DNA polymerase synthesizes DNA, it doesn't cleave it.

The correct answer is (B) Endonuclease, specifically restriction enzymes that create "sticky ends" for recombinant DNA technology.

Answer 2

Endonucleases are enzymes that cleave phosphodiester bonds within a nucleic acid strand, typically in the middle of a DNA molecule. These enzymes are used to cut plasmids or DNA into smaller fragments.

• Ligase is an enzyme used to join two strands of DNA.
• Exonuclease removes nucleotides from the ends of DNA molecules.
• Polymerase is used to synthesize DNA or RNA by adding nucleotides to the ends of the strand.

Option (B) is correct because endonucleases are responsible for cleaving plasmids.