Which enzyme is required for separating the DNA molecule into two strands during replication?

The enzyme crucial for separating the DNA molecule into two strands during replication is helicase. During the process of DNA replication, helicase unwinds the double helix structure of DNA by breaking the hydrogen bonds between the complementary base pairs. This unwinding creates two single strands of DNA, allowing other enzymes, such as DNA polymerase, to synthesize new complementary strands.

Understanding the roles of other enzymes is essential. DNA ligase, for example, is responsible for joining together the Okazaki fragments on the lagging strand after the DNA has been replicated. DNA polymerase is involved in adding nucleotides to the growing DNA strand but does not play a direct role in unwinding the DNA. Topoisomerase helps relieve torsional strain in the DNA molecule during replication by making cuts in the DNA strands, allowing them to rotate and relieve supercoiling, but it does not separate the strands itself.

Thus, helicase is specifically the enzyme that initiates the unwinding of DNA, making it the correct answer.