Which enzyme is responsible for joining segments of DNA together?

The enzyme that is responsible for joining segments of DNA together is DNA ligase. This enzyme plays a crucial role in DNA replication and repair. During the replication process, DNA ligase forms phosphodiester bonds between the Okazaki fragments on the lagging strand, effectively sealing nicks in the sugar-phosphate backbone and ensuring that the DNA remains a continuous strand. Additionally, in DNA repair processes, DNA ligase helps to connect segments of DNA that have been separated or damaged, thus playing a vital role in maintaining the integrity of the genetic material.

In contrast, DNA polymerase is primarily involved in synthesizing new DNA strands by adding nucleotides complementary to a template strand. Helicase unwinds the DNA double helix, separating the two strands so that replication can occur. Endonuclease is an enzyme that cleaves the phosphodiester bond within a nucleic acid strand, typically involved in processes such as DNA repair or restriction digestion. Each of these enzymes has a specific and distinct function within the broader context of DNA metabolism, making DNA ligase the correct choice for the function of joining DNA segments.