In prokaryotes, replication of DNA occurs in a process called semiconservative replication, meaning that each newly synthesized DNA molecule contains one strand from the original DNA molecule and one newly synthesized strand. The process involves several steps and requires the activity of various enzymes. Here is an overview of the mechanism, steps, and enzymes involved in DNA replication in prokaryotes:
1. Initiation:
- The replication of DNA initiates at a specific site called the origin of replication (oriC).
- The protein initiator DnaA binds to the oriC and opens up a short stretch of DNA, creating a replication bubble.
- Helicase (DnaB) then binds to the unwound DNA strands and separates them, forming a replication fork.
2. Elongation:
- DNA polymerase III (Pol III) binds to the unwound DNA at the replication fork.
- Primase (DnaG) synthesizes RNA primers that are complementary to the DNA template strands.
- DNA polymerase III adds nucleotides to the 3' end of the RNA primers, synthesizing new DNA strands in the 5' to 3' direction.
- The leading strand is synthesized continuously in the same direction as the replication fork movement.
- The lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, which are later joined together.
3. Termination:
- DNA replication proceeds bidirectionally along the DNA template until two replication forks meet at a specific site called the termination site (ter).
- Tus protein (termination utilization substance) binds to the ter sites and blocks the replication fork movement.
4. Enzymes involved:
- DnaA: Initiator protein that binds to the oriC and helps in the initiation of DNA replication.
- Helicase (DnaB): Unwinds the DNA double helix at the replication fork.
- Primase (DnaG): Synthesizes RNA primers that are complementary to the DNA template strands, providing the necessary starting point for DNA synthesis.
- DNA polymerase III (Pol III): Main DNA polymerase responsible for DNA synthesis during replication.
- DNA polymerase I (Pol I): Removes RNA primers and replaces them with DNA nucleotides.
- DNA ligase: Joins the Okazaki fragments on the lagging strand by catalyzing the formation of phosphodiester bonds.
- Topoisomerases: Relieves the tension caused by unwinding DNA during replication.
This mechanism ensures accurate replication of the entire DNA molecule in prokaryotes during each cell division, allowing for the transmission of genetic material to daughter cells.
replication of DNA in prokaryotes and its mechanism, steps and enzymes involved in the process
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