Arrange the events in the order that they occur during DNA replication.
The Correct Answer and Explanation is:
DNA replication is a highly coordinated process that ensures the accurate copying of genetic information. The process can be divided into several key stages:
- Initiation: Replication begins at specific locations on the DNA called “origins of replication.” The enzyme helicase unwinds the double-stranded DNA by breaking the hydrogen bonds between the complementary base pairs, creating a “replication bubble” with two replication forks. Single-strand binding proteins (SSBs) bind to the separated strands to prevent them from rejoining.
- Primer synthesis: An enzyme called primase synthesizes short RNA primers on the single-stranded DNA template. These primers provide a starting point for DNA polymerase, which cannot initiate DNA synthesis without a primer.
- Elongation: The enzyme DNA polymerase III adds nucleotides to the 3′ end of the RNA primer, creating a new complementary strand in the 5′ to 3′ direction. This occurs continuously on the leading strand, which is synthesized toward the replication fork. On the lagging strand, which is synthesized in the opposite direction, Okazaki fragments are formed. These are short segments of DNA synthesized by DNA polymerase III in the 5′ to 3′ direction.
- Primer removal and replacement: The RNA primers are removed by the enzyme DNA polymerase I, and the gaps are filled in with DNA nucleotides. DNA polymerase I also proofreads the newly synthesized DNA to correct any errors.
- Ligation: The enzyme DNA ligase seals the nicks between the Okazaki fragments, forming a continuous strand of DNA on the lagging strand.
- Termination: DNA replication ends when the replication forks meet, or when the replication process reaches a specific sequence that signals the termination. At this point, the newly synthesized DNA strands are proofread and checked for any remaining errors.
This process ensures that each daughter cell receives an exact copy of the DNA from the parent cell.
