A biochemist isolated and purified molecules needed for DNA replication. When some DNA was added, replication occurred but the DNA molecules formed were defective. Each consisted of a normal DNA strand paired with segments of DNA a few hundred nucleotides long. Which of the following had been left out of the mixture?

A. DNA ligase
B. Helicase
C. Nucleotides
D. DNA polymerase

The correct answer is option A, that is, DNA ligase.

Explanation:

It is clear that in the given mixture the researcher failed to add DNA ligase, due to which the obtained DNA molecules post replication were defective. In the process of replication, the enzyme known as DNA ligase plays an essential role in repairing breaks or abnormalities that appear in the DNA strands backbone. Thus, the enzyme has an essential function both in the process of replication and DNA repair.  

The enzyme DNA ligase performs its role by sealing recombination fragments, by repairing any abnormalities arising in the DNA, and by joining together the Okazaki fragments. The DNA ligase produces a linkage between the donor nucleotide terminal and the acceptor nucleotide terminal.