Primase

Definition

Primase is an enzyme that synthesizes short RNA primers during DNA replication, providing a starting point for DNA polymerases to elongate new DNA strands. It plays a critical role in both prokaryotic and eukaryotic organisms by ensuring that DNA synthesis can proceed efficiently and accurately.

5 Must Know Facts For Your Next Test

1. Primase synthesizes RNA primers that are approximately 5-10 nucleotides long, which are essential for initiating the process of DNA replication.
2. In prokaryotes, primase is often part of a larger complex called the primase-polymerase complex, which streamlines the replication process.
3. In eukaryotes, there are multiple types of primases, including the specialized primase found in the leading strand and different ones for Okazaki fragments.
4. The activity of primase is tightly regulated to prevent excess RNA primer synthesis, which could lead to genome instability.
5. Once the RNA primers are synthesized, they are later removed and replaced with DNA by other enzymes, allowing for a seamless continuation of DNA synthesis.

Review Questions

• How does primase contribute to the overall process of DNA replication?
  • Primase plays a crucial role in DNA replication by synthesizing short RNA primers, which serve as starting points for DNA polymerases. These primers are necessary because DNA polymerases can only add nucleotides to an existing strand. By providing these primers on both leading and lagging strands, primase ensures that replication proceeds smoothly and efficiently.
• Compare the function of primase in prokaryotic and eukaryotic DNA replication.
  • In prokaryotes, primase works as part of a primase-polymerase complex, synthesizing RNA primers quickly as the replication fork opens. In contrast, eukaryotes have multiple primases, each specialized for different types of replication—one for the leading strand and others for synthesizing Okazaki fragments on the lagging strand. This complexity reflects the differences in replication mechanisms between prokaryotic and eukaryotic cells.
• Evaluate the implications of malfunctioning primase on cellular function and genome integrity.
  • If primase malfunctions, it can lead to insufficient or excessive RNA primer synthesis during DNA replication. Insufficient primers can stall the replication process, while excessive synthesis may create unnecessary RNA segments that complicate subsequent DNA repair processes. Such issues can compromise genome integrity, potentially resulting in mutations or even cell death. Thus, proper functioning of primase is essential for maintaining cellular health and genomic stability.

Related terms

DNA polymerase:

An enzyme that catalyzes the synthesis of new DNA strands by adding nucleotides to a growing chain, using an existing strand as a template.

Okazaki fragments:

Short segments of DNA synthesized on the lagging strand during DNA replication, which are later joined together by DNA ligase.

helicase:

An enzyme that unwinds and separates the double-stranded DNA, creating two single strands for replication to occur.