Describe DNA replication in prokaryotes. Include the major steps for origins of replication, unwinding DNA, and synthesis of new strands. Include at least 1 simplified diagram.
DNA replication in prokaryotes is a highly regulated process that ensures accurate duplication of the genetic material during cell division. It involves multiple steps, including the identification of origins of replication, unwinding of the DNA double helix, and synthesis of new strands.
1. Origins of replication: The replication process initiates at specific sites in the DNA called origins of replication (Ori). In prokaryotes, such as bacteria, there is usually a single Ori site in the circular DNA molecule. The replication initiation proteins, like DnaA, bind to the Ori and begin unwinding the DNA strands.
2. Unwinding DNA: Once bound to the Ori, the replication initiation proteins recruit other proteins called helicases. These helicases use ATP energy to unwind and separate the two DNA strands, generating a replication bubble. Within the bubble, the parental DNA strands act as the template for copying.
3. Synthesis of new strands: Each separated DNA strand now serves as a template for the synthesis of new complementary strands. The process of synthesizing new strands is carried out by DNA polymerases. The main DNA polymerase involved in prokaryotic replication is DNA polymerase III.
- Leading strand synthesis: On the leading strand, DNA synthesis occurs continuously in a 5' to 3' direction, which is the same direction as the replication fork's movement. DNA polymerase III synthesizes a continuous new strand by adding nucleotides one after another.
- Lagging strand synthesis: On the lagging strand, which is synthesized in the opposite direction of the replication fork, DNA is synthesized in small fragments called Okazaki fragments. Primase synthesizes RNA primers that DNA polymerase III then extends to synthesize short stretches of DNA. These Okazaki fragments are later sealed together by an enzyme called DNA ligase.
Here is a simplified diagram of DNA replication in prokaryotes:
Parental DNA
(Template Strands)
_________________________
| |
| ----DNA replication----> |
|_________________________|
Leading Strand Lagging Strand (Okazaki fragments)
It's important to note that prokaryotic DNA replication is a complex process involving several other proteins and enzymes that assist in stabilizing the replication fork and ensuring accurate copying of the genetic information.