Which enzyme is crucial for joining Okazaki fragments on the lagging strand during DNA replication?

The enzyme that is crucial for joining Okazaki fragments on the lagging strand during DNA replication is ligase. During DNA replication, the lagging strand is synthesized discontinuously in segments called Okazaki fragments. After these fragments are synthesized, they are not yet continuous; therefore, ligase plays a vital role in sealing the gaps between them. This enzyme catalyzes the formation of phosphodiester bonds between the sugar and phosphate groups of adjacent nucleotides, effectively "gluing" the fragments together to form a continuous strand of DNA.

Polymerase, on the other hand, is responsible for adding nucleotides to the growing DNA strand but does not perform the task of joining fragments. Helicase is involved in unwinding the DNA double helix, allowing the polymerase access to the template strands, but it does not participate in joining Okazaki fragments. DNAase, which is involved in degrading DNA, does not contribute to the replication process in this context. Thus, ligase is the key enzyme needed to ensure that the DNA strands are properly joined and complete.