Question

What is the function of primase? a. synthesis of the short section of double-stranded DNA required by DNA polymerase b. synthesis of a short RNA strand that is complementary to singlestranded DNA c. closing the gap at the \(3^{\prime}\) end of DNA after excision repair d. removing primers and synthesizing a short section of DNA to replace them

Short answer

The function of primase is the synthesis of a short RNA strand that is complementary to single-stranded DNA. This short RNA strand, called a primer, is essential for DNA polymerase to synthesize the new DNA strand. Therefore, the correct answer is option (b).

Step-by-step solution

Understand the function of Primase

Primase is an essential enzyme for the process of DNA replication. It plays an essential role in the initiation of DNA replication by synthesizing a short RNA strand that is complementary to the single-stranded DNA template. This formed RNA strand is called a primer. The DNA polymerase then uses this primer to synthesize the new DNA strand, as it requires a hydroxyl group on the 3' end to begin the synthesis. Now let's analyze the given options:

Option (a)

"synthesis of the short section of double-stranded DNA required by DNA polymerase" - This statement describes the role of DNA polymerase, not primase. DNA polymerase is responsible for synthesizing new DNA strands using the original DNA as a template. Hence, this option is incorrect.

Option (b)

"synthesis of a short RNA strand that is complementary to single-stranded DNA" - This statement accurately describes the primary role of primase. As mentioned earlier, it synthesizes a short RNA strand, called a primer, which is complementary to single-stranded DNA. Hence, this option is correct.

Option (c)

"closing the gap at the \(3^{\prime}\) end of DNA after excision repair" - This statement describes the role of DNA ligase, which is an enzyme responsible for sealing gaps and joining DNA strands by forming covalent bonds. This is not the function of primase, so this option is incorrect.

Option (d)

"removing primers and synthesizing a short section of DNA to replace them" - This statement describes the role of RNase H and DNA Polymerase I in prokaryotes, and of RNase H and DNA Polymerase δ/ε in eukaryotes. They are responsible for removing the primer and filling the gaps with newly synthesized DNA. This is not the function of primase, so this option is incorrect. Based on the analysis, the correct option is: b. synthesis of a short RNA strand that is complementary to single-stranded DNA

Key concepts

Primase function

In the fascinating world of DNA replication, primase plays a pivotal role in kickstarting the process. It is an enzyme that lays the groundwork for DNA synthesis by creating short RNA strands. These strands act as primers. Primase identifies a specific starter point on the DNA template. It attaches itself and begins synthesizing a short RNA sequence.
This RNA primer is vital because it serves as a starting point for DNA polymerase. The synthesis process initiated by primase is essential. It allows the DNA polymerase enzyme to attach and start adding DNA nucleotides. Without the primer, the replication process would halt. Primase, therefore, ensures the DNA strands are accurately duplicated and plays a key role in genetic inheritance.

DNA polymerase

DNA polymerase is another vital enzyme in DNA replication. Once primase has done its job, DNA polymerase takes over. It adds nucleotides one-by-one to the 3' end of the existing RNA primer. This process elongates the new DNA strand. DNA polymerase is highly efficient and ensures high fidelity during replication.
A few key points about DNA polymerase:

• It reads the template DNA strand in the 3' to 5' direction.
• It synthesizes the new DNA in the 5' to 3' direction.
• It has proofreading abilities to minimize errors.

Moreover, different types of DNA polymerases exist, each with specific roles in replication and repair.

RNA primer synthesis

RNA primer synthesis is crucial during DNA replication because it provides a starting block for DNA polymerase. Primase synthesizes these primers by making short RNA sequences complementary to the DNA template.
A few notable points about RNA primer synthesis:

• Primers are typically 5 to 10 nucleotides long.
• They are composed of RNA nucleotides, which get replaced later by DNA nucleotides.
• The primer provides a 3' hydroxyl (OH) group needed for DNA polymerase to begin DNA synthesis.

This RNA primer is like a scaffolding providing the necessary support for DNA polymerase to launch into action. It captures the essence of teamwork in the DNA replication process, where each component must cooperate to ensure successful cell division.