Introduction

DNA replication in eukaryotic cells is a highly orchestrated process involving several key enzymes. One of the critical steps in replication is the removal of the RNA primers that are initially synthesized to begin the DNA synthesis process. These RNA primers must be removed to ensure the continuity of the newly synthesized DNA strand. In this article, we’ll discuss how the RNA primer is degraded during eukaryotic DNA replication and the key enzyme responsible for this process: FEN-1 (Flap Endonuclease 1).

RNA Primer Removal in Eukaryotic DNA Replication

During DNA replication, the enzyme DNA polymerase requires a primer to initiate synthesis. In eukaryotic cells, the primer is made of RNA and provides the necessary 3′ OH group for DNA polymerase to start adding nucleotides. Once the primer has been used to initiate DNA synthesis, it needs to be removed to allow the proper formation of the newly synthesized DNA strand.

Role of FEN-1 in RNA Primer Removal

FEN-1 (Flap Endonuclease 1) is a crucial enzyme that plays a major role in the removal of RNA primers during replication. FEN-1 possesses 5′ to 3′ exonuclease activity, which allows it to degrade the RNA primers. The process works as follows:

1. After the primer has been synthesized, DNA polymerase extends the DNA strand and displaces the RNA primer, creating a flap-like structure.

2. FEN-1 recognizes this flap and removes the RNA primer by cleaving the 5′ end, ensuring that the newly synthesized DNA strand is continuous.

3. This action of FEN-1 is essential for maintaining the integrity of the replicated DNA and ensuring accurate DNA synthesis.

Other Enzymes in RNA Primer Removal

While FEN-1 is the main enzyme responsible for RNA primer degradation, there are other enzymes involved in the replication process:

• RNAse H1: This enzyme has a role in degrading the RNA strand of RNA-DNA hybrids, but it is not responsible for the 5′ to 3′ exonuclease activity required to remove the RNA primer during replication.

• DNA Polymerase V: This polymerase is involved in translesion synthesis and is not directly related to primer removal.

• Topoisomerase IIB: This enzyme helps alleviate the tension generated ahead of the replication fork but does not participate in RNA primer removal.

Thus, FEN-1 is the key enzyme responsible for RNA primer degradation during eukaryotic DNA replication.

Answer to the Question

Given the options provided, the correct answer is:

(b) FEN-1

Conclusion

The accurate and efficient removal of RNA primers is critical for the proper completion of DNA replication in eukaryotic cells. FEN-1, with its 5′ to 3′ exonuclease activity, plays an essential role in this process. By removing the RNA primer, FEN-1 ensures that the newly synthesized DNA strand is complete and uninterrupted, contributing to the fidelity and efficiency of DNA replication. Understanding the role of FEN-1 and its mechanism of action helps in appreciating the complexity of DNA replication and the precision required for cellular division and function.

Answer:

The correct answer is:
(b) FEN-1