What description of DNA replication is correct?
a. The two strands of DNA separate and restriction enzymes cut up one strand. Then the DNA uses these pieces to synthesize two new strands out of the old one.
b. The two strands of DNA separate, and each one receives a complementary strand of RNA. Then the new RNA strands serve as templates for the assembly of many new DNA strands.
c. Ligase separates the two strands of the DNA double helix. Then DNA polymerase synthesizes the leading strands and primase synthesizes the lagging strand.
d. Helicases separate the two strands of the double helix, and DNA polymerases use each of the original strands as templates to create two new strands.
The Correct Answer and Explanation is :
The correct answer is d. Helicases separate the two strands of the double helix, and DNA polymerases use each of the original strands as templates to create two new strands.
Explanation:
DNA replication is the process by which a cell copies its DNA before cell division, ensuring that both daughter cells receive identical genetic information. Here is a breakdown of how it works:
- Helicases: The first step in DNA replication involves the enzyme helicase, which unwinds and separates the two strands of the DNA double helix. This creates a “replication fork,” where the two strands are open and available to be used as templates for replication.
- DNA polymerases: Once the strands are separated, DNA polymerases (specifically DNA polymerase III in prokaryotes and DNA polymerase δ and ε in eukaryotes) come into play. These enzymes move along each strand and use them as templates to synthesize complementary new strands. DNA polymerase can only add nucleotides to an existing strand, so an RNA primer is laid down by primase to start the replication process.
- Leading strand: On the leading strand, DNA polymerase moves continuously in the same direction as the replication fork, adding nucleotides one by one to create a new strand.
- Lagging strand: On the lagging strand, DNA polymerase moves in the opposite direction of the replication fork. Since DNA replication is always 5′ to 3′, the lagging strand is synthesized in short segments known as Okazaki fragments, which are later joined together by DNA ligase.
- Result: The result of DNA replication is two identical DNA molecules, each containing one original strand and one newly synthesized strand. This process is called semi-conservative replication because each new DNA molecule conserves one strand of the original DNA.
This process is highly coordinated and involves a variety of enzymes and proteins to ensure accuracy and efficiency in copying the genetic material.