In recombinant DNA cloning, what enzyme covalently seals phosphodiester backbone nicks between adjacent Okazaki fragments or insert and vector DNA?
Answer and explanation
Correct answer: B. DNA ligase
- Step 1: When restriction endonucleases generate cohesive or blunt ends, complementary bases anneal via hydrogen bonding. Step 2. DNA ligase catalyzes formation of a phosphodiester bond between the adjacent 3'-OH and 5'-phosphate groups, requiring ATP or NAD+. Answer: DNA ligase. Why not the others: Alkaline phosphatase removes 5' phosphates; reverse transcriptase synthesizes cDNA from RNA; Taq polymerizes nucleotides.
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