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

The enzyme used to join two DNA fragments in genetic engineering is DNA ligase. Here's how it works:

1. Function of DNA Ligase: DNA ligase is an enzyme that creates phosphodiester bonds between DNA strands, thus sealing breaks in the DNA backbone. It is crucial for connecting DNA fragments during the formation of recombinant DNA.
2. Role in Genetic Engineering: In genetic engineering, DNA ligase is employed to join DNA fragments that have been cut by restriction enzymes at specific sites. After restriction endonucleases cut the DNA, DNA ligase helps to recombine these fragments back together to form new sequences.
3. Comparison with Other Options:
   • Restriction Endonuclease: This enzyme cuts DNA at specific sequences, but does not join DNA fragments.
   • DNA Polymerase: This enzyme synthesizes new DNA strands by adding nucleotides, but does not join fragments.
   • RNA Polymerase: This enzyme synthesizes RNA from a DNA template, but is not involved in joining DNA fragments.
4. Conclusion: Given these functions, DNA ligase is the correct and appropriate choice for joining DNA fragments in genetic engineering. The role of DNA ligase is irreplaceable in most cloning processes, where precise joining of DNA is required to produce a stable recombinant DNA molecule.

Answer 2

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.