In recombinant DNA-based genetic cloning, two enzymes commonly required to cut DNA and then join DNA fragments are which of the following pairs?

• A. A restriction endonuclease and DNA ligase
• B. Helicase and topoisomerase
• C. DNA polymerase and RNA polymerase
• D. Reverse transcriptase and primase

Answer: (A)

Verified step by step guidance

1. Understand the role of enzymes in recombinant DNA technology: the process involves cutting DNA at specific sites and then joining DNA fragments together.
2. Identify the enzyme responsible for cutting DNA at specific sequences; this enzyme is known as a restriction endonuclease (or restriction enzyme), which recognizes specific DNA sequences and makes precise cuts.
3. Recognize the enzyme that joins DNA fragments by forming phosphodiester bonds between the sugar-phosphate backbones; this enzyme is DNA ligase, which seals the nicks in the DNA strands.
4. Eliminate other enzyme pairs based on their functions: helicase unwinds DNA, topoisomerase relieves supercoiling, DNA polymerase synthesizes DNA, RNA polymerase synthesizes RNA, reverse transcriptase synthesizes DNA from RNA, and primase synthesizes RNA primers.
5. Conclude that the correct pair of enzymes required for cutting and joining DNA fragments in recombinant DNA cloning is a restriction endonuclease and DNA ligase.