Question

Which one is joining or repair enzyme?

• A. DNA kinase
• B. DNA ligase
• C. DNA polymerase
• D. Transcriptase

Answer 1

The correct option is B DNA ligase

DNA kinase catalyzes the transfer of phosphate groups from high-energy, phosphate-donors to DNA thereby causing its phosphorylation; ATP is the most common phosphate donor; Option A is incorrect. DNA ligase enzyme joins two DNA fragments together via phosphodiester bond between 3’ hydroxyl at the end of one fragment and a 5’ phosphate at the end of another fragment; it joins DNA fragments separated by DNA polymerase I during repair mechanism which makes option B correct. DNA polymerase enzyme adds deooxyribonucleotides to 3’ hydroxyl end of a primer using the base sequence of parental DNA strand during DNA replication; it does not ligate two DNA strands. Option C is incorrect. RNA retroviruses have reverse transcriptase enzyme that synthesizes a DNA copy (cDNA) of viral RNA using RNA as template; it is DNA polymerizing enzyme and do not play any role in joining DNA fragments or its repair which makes option D wrong. Correct answer is B.