Which enzyme polymerises okazaki fragments ?
**Core Concept**
DNA synthesis during the S phase of the cell cycle requires the continuous unwinding of the double helix and the assembly of short RNA primers onto which DNA nucleotides are added. This process is crucial for maintaining the integrity of the genome and ensuring accurate replication. The enzyme responsible for polymerizing Okazaki fragments, which are short, discontinuous DNA strands synthesized on the lagging strand, is a key component of this process.
**Why the Correct Answer is Right**
The enzyme responsible for polymerizing Okazaki fragments is DNA polymerase delta (Pol δ). This enzyme is a multifunctional enzyme that possesses both polymerase and 3'-5' exonuclease proofreading activities. Pol δ plays a crucial role in the replication of the lagging strand by synthesizing short, discontinuous DNA fragments (Okazaki fragments) and then linking them together through the action of DNA ligase. The process involves the removal of RNA primers by RNase H and the repair of any errors that occur during DNA synthesis.
**Why Each Wrong Option is Incorrect**
**Option A:** DNA polymerase alpha (Pol α) is responsible for initiating DNA synthesis on both the leading and lagging strands by adding short RNA primers. While it is involved in the early stages of DNA replication, it is not responsible for polymerizing Okazaki fragments.
**Option B:** Topoisomerase is an enzyme that relaxes supercoiled DNA by cutting and rejoining the phosphodiester backbone. While it plays a crucial role in DNA replication, it is not directly involved in the polymerization of Okazaki fragments.
**Option C:** DNA ligase is an enzyme that seals the gaps between Okazaki fragments by forming a phosphodiester bond between the 3'-end of one fragment and the 5'-end of the adjacent fragment. While it is essential for linking Okazaki fragments together, it is not responsible for polymerizing them.
**Clinical Pearl / High-Yield Fact**
DNA replication is a highly regulated process that involves the coordinated action of multiple enzymes, including DNA polymerase delta, DNA ligase, and topoisomerase. Understanding the roles of these enzymes is crucial for grasping the underlying mechanisms of DNA replication and repair.
**Correct Answer:** C. DNA ligase is not the correct answer, however, the correct answer to your prompt is not provided.