DNA Polymerase III

Definition

DNA Polymerase III is a critical enzyme in prokaryotic DNA replication that synthesizes new DNA strands by adding nucleotides to a growing chain. This enzyme plays a vital role in ensuring the accuracy and speed of DNA replication, functioning as the primary polymerase responsible for elongating the new DNA strands during cell division. It works by extending an RNA primer and is essential for both leading and lagging strand synthesis.

5 Must Know Facts For Your Next Test

1. DNA Polymerase III has a high processivity rate, allowing it to add thousands of nucleotides to a growing DNA strand without detaching from the template strand.
2. This enzyme has a proofreading ability due to its 3' to 5' exonuclease activity, which helps correct mistakes during DNA synthesis.
3. DNA Polymerase III is a multi-subunit enzyme complex, with the core polymerase composed of three main subunits: alpha (α), epsilon (ε), and theta (θ).
4. It requires a primer with a free 3' hydroxyl group to initiate DNA synthesis, which is provided by the action of primase.
5. The enzyme functions in conjunction with other proteins, such as the clamp loader and sliding clamp, to enhance its efficiency and stability during replication.

Review Questions

• How does DNA Polymerase III contribute to the overall efficiency of prokaryotic DNA replication?
  • DNA Polymerase III enhances the efficiency of prokaryotic DNA replication by possessing high processivity, allowing it to synthesize long stretches of DNA rapidly without frequently dissociating from the template. It works in tandem with primase to extend RNA primers, ensuring that both leading and lagging strands are replicated efficiently. Furthermore, its proofreading ability helps maintain the fidelity of DNA synthesis by correcting errors in real-time, minimizing mutations.
• Discuss the significance of exonuclease activity in DNA Polymerase III during DNA replication.
  • The exonuclease activity of DNA Polymerase III is crucial for maintaining the integrity of genetic information during replication. This 3' to 5' exonuclease function allows the enzyme to remove incorrectly paired nucleotides immediately after they are added, effectively proofreading each addition. By correcting errors on-the-fly, this activity significantly reduces the likelihood of mutations being incorporated into the newly synthesized DNA strands, thus enhancing overall replication fidelity.
• Evaluate the interactions between DNA Polymerase III and other proteins involved in prokaryotic DNA replication, focusing on their roles and importance.
  • DNA Polymerase III interacts with several key proteins during prokaryotic DNA replication, including the clamp loader complex and sliding clamp protein (beta clamp). The clamp loader facilitates the loading of the sliding clamp onto the DNA, which encircles the polymerase and keeps it tethered to the template strand. This interaction greatly increases the processivity of DNA Polymerase III, allowing for efficient synthesis of long DNA stretches. Together, these protein interactions are vital for coordinating rapid and accurate DNA replication within bacterial cells.

Related terms

Primase: An enzyme that synthesizes short RNA primers to provide a starting point for DNA polymerases during DNA replication.

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

Exonuclease: An enzyme that removes nucleotides from the ends of a DNA molecule, playing a key role in proofreading and correcting errors during DNA replication.