DNA polymerase III

Definition

DNA polymerase III is a crucial enzyme involved in DNA replication, responsible for synthesizing new DNA strands by adding nucleotides to a growing chain. This enzyme plays a vital role during the elongation phase of DNA replication, ensuring that the genetic information is accurately copied and maintained in the daughter cells.

5 Must Know Facts For Your Next Test

1. DNA polymerase III has high fidelity, meaning it accurately incorporates nucleotides and has proofreading capabilities to correct errors during replication.
2. It requires a primer with a free 3' hydroxyl group to initiate DNA synthesis, which is provided by primase.
3. The enzyme has multiple subunits that form a complex, allowing it to have a high processivity, meaning it can synthesize long stretches of DNA without falling off.
4. DNA polymerase III is essential for both leading and lagging strand synthesis during replication, contributing to the overall efficiency of the process.
5. In bacteria, DNA polymerase III is the primary enzyme used during chromosomal DNA replication, while other types of polymerases handle different functions such as repair.

Review Questions

• How does DNA polymerase III ensure accuracy during DNA replication?
  • DNA polymerase III ensures accuracy during DNA replication through its high fidelity, which allows it to correctly incorporate nucleotides complementary to the template strand. Additionally, it possesses proofreading activity; if an incorrect nucleotide is added, the enzyme can detect this mistake and remove it before continuing with the synthesis. This dual mechanism greatly reduces the error rate in newly synthesized DNA.
• Discuss the roles of leading and lagging strands in relation to DNA polymerase III's function during replication.
  • During DNA replication, DNA polymerase III synthesizes both leading and lagging strands. The leading strand is synthesized continuously in the direction of the replication fork, allowing for efficient elongation. In contrast, the lagging strand is synthesized discontinuously in short segments known as Okazaki fragments. DNA polymerase III adds nucleotides to these fragments and later connects them with ligase, highlighting its versatility in handling different strand synthesis mechanisms.
• Evaluate the significance of DNA polymerase III's structure and function in bacterial DNA replication compared to eukaryotic systems.
  • The structure and function of DNA polymerase III are crucial for bacterial DNA replication efficiency. Its multi-subunit composition allows for high processivity, enabling rapid synthesis of long DNA strands. In contrast, eukaryotic cells employ multiple types of DNA polymerases with distinct roles, including those for replication, repair, and mitochondrial DNA synthesis. This difference underscores how prokaryotic systems rely on a single enzyme for primary replication tasks, while eukaryotic systems require more specialized enzymes due to their larger and more complex genomes.

Related terms

DNA replication fork: The Y-shaped region where the double helix of DNA is unwound and where the new strands of DNA are synthesized.

Leading strand: The strand of DNA that is synthesized continuously in the same direction as the movement of the replication fork.

Lagging strand: The strand of DNA that is synthesized discontinuously in short segments, known as Okazaki fragments, in the opposite direction of the replication fork.