Primase

Definition

Primase is an enzyme that synthesizes short RNA primers during DNA replication, providing a starting point for DNA polymerase to extend and synthesize the new DNA strand. This enzyme is essential because DNA polymerases can only add nucleotides to an existing strand of nucleic acid, making primase crucial for initiating DNA synthesis.

5 Must Know Facts For Your Next Test

1. Primase specifically synthesizes RNA primers that are about 5-10 nucleotides long, which are necessary for DNA polymerases to begin DNA synthesis.
2. In prokaryotes, primase is often a part of a multi-enzyme complex known as the primase-polymerase complex, whereas eukaryotes have a separate primase enzyme.
3. The activity of primase is crucial during both leading and lagging strand synthesis; it lays down primers on both strands to enable continuous and discontinuous DNA synthesis.
4. After the RNA primers are laid down, they are later removed and replaced with DNA nucleotides by another enzyme called DNA polymerase.
5. Primase acts in coordination with other enzymes involved in DNA replication, ensuring that the replication fork progresses smoothly and accurately.

Review Questions

• How does primase facilitate the process of DNA replication and what would happen if it were not present?
  • Primase plays a vital role in DNA replication by synthesizing RNA primers that provide the necessary starting points for DNA polymerases to begin adding nucleotides. Without primase, DNA polymerases would be unable to initiate synthesis, leading to incomplete replication of the genome. Consequently, cells would be unable to divide properly, which could result in cell death or malfunction.
• Compare the roles of primase and DNA polymerase during DNA replication.
  • Primase and DNA polymerase have distinct yet interconnected roles during DNA replication. Primase synthesizes short RNA primers that are essential for initiating the process, while DNA polymerase is responsible for extending those primers by adding complementary nucleotides to form new DNA strands. The function of primase ensures that there are starting points for DNA polymerases to work effectively, making both enzymes crucial for successful replication.
• Evaluate the significance of RNA primers synthesized by primase in the context of leading and lagging strand synthesis.
  • The significance of RNA primers synthesized by primase lies in their role in facilitating both leading and lagging strand synthesis during DNA replication. On the leading strand, a single primer allows continuous synthesis, while on the lagging strand, multiple primers are required to initiate the synthesis of Okazaki fragments. This alternating pattern ensures that both strands are replicated accurately and efficiently, highlighting how primase is essential for maintaining genome integrity through proper replication processes.

Related terms

DNA Polymerase: An enzyme responsible for synthesizing new DNA strands by adding nucleotides complementary to the template strand during DNA replication.

Helicase: An enzyme that unwinds and separates the double-stranded DNA into single strands, allowing replication to occur.

Okazaki Fragments: Short segments of newly synthesized DNA on the lagging strand during replication, which are initiated by RNA primers laid down by primase.