Final answer:
Helicase is responsible for unwinding the DNA double helix by breaking hydrogen bonds between base pairs, which allows replication machinery to access the DNA strands. Topoisomerase alleviates tension from unwinding, and a mutation in helicase can prevent strand separation and halt replication.
Step-by-step explanation:
The function of helicase in DNA replication is to separate the two DNA strands at the origin of replication. This unwinding process is crucial for allowing the replication machinery access to the template strands. Helicase accomplishes this by breaking the hydrogen bonds between the nucleotide base pairs, thereby opening up the double helix.
Once the DNA is unwound, other proteins such as single-strand binding proteins attach to the separated strands to prevent them from reannealing. Meanwhile, topoisomerase prevents supercoiling ahead of the replication fork by causing temporary breaks in the DNA strands and then sealing them again. This alleviates the tension resulting from the unwinding process.
Following this initial step, primase synthesizes an RNA primer, facilitating the attachment of DNA polymerase, which then begins the synthesis of the new DNA strand. When a helicase is mutated and loses its function, the DNA strands fail to separate at the start of replication, which impedes the entire process.