Question

Which enzyme is used to join two DNA fragments in genetic engineering?

• A. Restriction endonuclease
• B. DNA polymerase
• C. RNA polymerase
• D. DNA ligase

Hint:

Restriction enzymes cut DNA, while DNA ligase acts as the “molecular glue” to join DNA fragments.

Answer 1

The Correct Option is D

Step 1: Understanding genetic engineering.
Genetic engineering involves cutting DNA at specific sites and then joining desired DNA fragments to form recombinant DNA. This process requires specialized enzymes.
Step 2: Role of DNA ligase.
DNA ligase is an enzyme that joins DNA fragments by forming phosphodiester bonds between adjacent nucleotides. It seals the sugar-phosphate backbone, making the DNA continuous.
Step 3: Analysis of the given options.
(A) Restriction endonuclease: These enzymes cut DNA at specific recognition sites.
(B) DNA polymerase: This enzyme synthesizes new DNA strands but does not join fragments.
(C) RNA polymerase: It synthesizes RNA from a DNA template.
(D) DNA ligase: Correct — it joins two DNA fragments by forming phosphodiester bonds.
Step 4: Conclusion.
The enzyme used to join two DNA fragments in genetic engineering is DNA ligase.