Question

During DNA replication, a series of steps are required to ensure that the genetic information in a cell is correctly and accurately duplicated. Place the following phrases in the correct order.

Binding proteins stabilize the unwound double helix.

DNA helicase unwinds the DNA double helix.

Topoisomerase IV separates linked chromosomes.

DNA pol III adds complementary nucleotides.

DNA ligase seals any nicks in the DNA.

DNA pol I replaces the RNA primer.

Primase generates a RNA primer that binds to the origin.

Answer 1

Answer:

1. DNA helicase unwinds the DNA double helix.
2. Binding proteins stabilize the unwound double helix.
3. Primase generates a RNA primer that binds to the origin.
4. DNA pol III adds complementary nucleotides.
5. DNA pol I replaces the RNA primer.
6. DNA ligase seals any nicks in the DNA.
7. Topoisomerase IV separates linked chromosomes.

Explanation:

DNA replication begins with unwinding of DNA strands at the replication fork by DNA helicase so that the two strands are accessible to enzymes. Single strand binding proteins attach to the strands and prevent their rewinding. A type of topoisomerase also prevents supercoiling in the portion ahead of replication fork by creating nicks.

DNA pol III requires existing nucleotides to attach new nucleotides so a primase first synthesises a RNA primer complimentary to the DNA strand. DNA pol III further adds nucleotides to the primer complimentary to the DNA strand. After pol III finishes the process, the RNA primer is replaced by DNA nucleotides by DNA pol I. DNA ligase seals the gaps between DNA fragments. The two newly synthesised DNA strands become interlinked. Topoisomerase IV removes these links so that the chromosomes are segregated.