Primase

Definition

Primase is an enzyme that synthesizes short RNA primers during DNA replication, providing a starting point for DNA polymerases to extend and create new DNA strands. This enzyme is crucial for initiating the replication process, as DNA polymerases cannot start new strands on their own; they need a pre-existing primer. Primase plays a key role in ensuring the accurate and efficient duplication of DNA, which is vital for cell division and gene expression.

5 Must Know Facts For Your Next Test

1. Primase is a type of RNA polymerase that specifically synthesizes RNA primers necessary for DNA replication.
2. In eukaryotes, primase is part of a larger complex called the DNA polymerase α-primase complex, which helps to synthesize both the RNA primer and a short stretch of DNA.
3. Primase acts on both the leading and lagging strands, creating primers that allow DNA polymerases to elongate the new strands.
4. The RNA primers synthesized by primase are eventually removed and replaced with DNA nucleotides by another enzyme called DNA polymerase I in prokaryotes or RNase H in eukaryotes.
5. Primase has a high turnover rate, meaning it rapidly synthesizes multiple RNA primers to facilitate efficient DNA replication.

Review Questions

• How does primase contribute to the overall process of DNA replication?
  • Primase is essential in DNA replication because it synthesizes short RNA primers that provide a starting point for DNA polymerases. Without these primers, DNA polymerases would be unable to initiate synthesis, as they require a pre-existing strand to extend from. This function of primase ensures that both leading and lagging strands are replicated correctly, facilitating the accurate duplication of genetic material.
• Discuss the differences in primase function between prokaryotic and eukaryotic organisms during DNA replication.
  • In prokaryotic organisms, primase functions as a standalone enzyme that synthesizes RNA primers directly at the replication fork. In contrast, eukaryotic primase is part of a multi-enzyme complex that also includes DNA polymerase α. This complex not only synthesizes the RNA primer but also extends it with a short stretch of DNA. Additionally, eukaryotic cells have multiple origins of replication, leading to more complex regulation of primase activity compared to prokaryotic cells.
• Evaluate the impact of primase malfunction on cellular processes such as cell division and gene expression.
  • If primase malfunctions, it can lead to incomplete or inaccurate DNA replication, ultimately affecting cell division and genetic stability. Without proper RNA primers, DNA polymerases would be unable to initiate new strand synthesis, resulting in halted replication processes. This could cause cells to enter apoptosis or lead to mutations if the damage is not repaired. Additionally, because gene expression relies on accurate and complete DNA replication, any disruptions caused by faulty primase could affect the transcription of critical genes, impacting overall cellular function and health.

Related terms

DNA Polymerase: An enzyme that synthesizes new DNA strands by adding nucleotides to a pre-existing strand or primer.

Okazaki Fragments: Short segments of newly synthesized DNA on the lagging strand, which are created discontinuously and require primers for initiation.

RNA Primer: A short segment of RNA synthesized by primase that serves as the starting point for DNA synthesis during replication.