Primase

Definition

Primase is an enzyme that synthesizes short RNA primers during DNA replication, providing a starting point for DNA polymerase to begin elongation. This enzyme is crucial in the replication process, as it allows the synthesis of new DNA strands by providing the necessary free 3' hydroxyl group for nucleotides to be added. Primase ensures that replication can occur smoothly and efficiently on both leading and lagging strands.

5 Must Know Facts For Your Next Test

1. Primase synthesizes RNA primers that are typically about 5-10 nucleotides long, which are essential for initiating DNA synthesis.
2. The activity of primase is particularly important for the lagging strand, where multiple primers are required to create Okazaki fragments.
3. Primase operates in a complex with other proteins involved in DNA replication, ensuring coordinated action during the replication process.
4. Unlike DNA polymerases, primase does not require a free 3' hydroxyl group; it can initiate synthesis de novo.
5. The RNA primers laid down by primase are eventually removed and replaced with DNA nucleotides by another type of polymerase before the final joining of fragments.

Review Questions

• How does primase contribute to the overall process of DNA replication?
  • Primase plays a vital role in DNA replication by synthesizing short RNA primers that provide a starting point for DNA polymerases. These primers are essential for both the leading and lagging strands, allowing DNA polymerases to initiate elongation at the correct sites. By facilitating the addition of nucleotides to the growing DNA strands, primase ensures that replication can proceed efficiently and accurately.
• Discuss the significance of RNA primers synthesized by primase in relation to Okazaki fragments on the lagging strand.
  • The RNA primers created by primase are critical for forming Okazaki fragments on the lagging strand during DNA replication. Each Okazaki fragment starts with an RNA primer laid down by primase, which allows DNA polymerases to extend from these primers and synthesize short segments of DNA. This process is necessary because the lagging strand is synthesized discontinuously, requiring multiple primers to create these fragments that are later joined together to form a continuous strand.
• Evaluate how defects in primase activity could impact DNA replication and overall cellular function.
  • Defects in primase activity could lead to incomplete or erroneous synthesis of RNA primers, resulting in ineffective initiation of DNA replication. This could cause delays or failures in replicating essential genetic material, potentially leading to genomic instability, increased mutation rates, or cell death. In multicellular organisms, such issues could contribute to diseases such as cancer due to improper cell division and uncontrolled growth resulting from faulty replication processes.

Related terms

DNA Polymerase: An enzyme responsible for adding nucleotides to a growing DNA strand during DNA replication, using the 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.

Replication Fork: The Y-shaped region where the DNA double helix is unwound and separated into two single strands for replication.