What is the first step in DNA replication?

What is the first step in DNA replication?

• A. DNA Unwinds and Strands Separate
• B. RNA Primers Laid Down
• C. DNA Remains Double-Stranded
• D. DNA Gets Methylated

Answer: (A)

The first step in DNA replication is to unwind the DNA helix so each strand can serve as a template. Helicase breaks the hydrogen bonds between base pairs, separating the two strands and forming the replication fork. This opening is necessary because DNA polymerases can only synthesize new DNA using exposed bases on a template strand. As the strands separate, single-stranded binding proteins stabilize the unwound DNA, and topoisomerase relieves the tension from unwinding. Only after this unwinding can RNA primers be laid down to furnish a starting point for DNA synthesis, and then DNA polymerases begin copying the templates. The other options aren’t the initial action: primers come after unwinding, keeping the DNA double-stranded would prevent replication, and methylation isn’t the first step in initiating replication.

The first step in DNA replication is to unwind the DNA helix so each strand can serve as a template. Helicase breaks the hydrogen bonds between base pairs, separating the two strands and forming the replication fork. This opening is necessary because DNA polymerases can only synthesize new DNA using exposed bases on a template strand. As the strands separate, single-stranded binding proteins stabilize the unwound DNA, and topoisomerase relieves the tension from unwinding. Only after this unwinding can RNA primers be laid down to furnish a starting point for DNA synthesis, and then DNA polymerases begin copying the templates. The other options aren’t the initial action: primers come after unwinding, keeping the DNA double-stranded would prevent replication, and methylation isn’t the first step in initiating replication.