Dna polymerase i

Definition

DNA polymerase I is an enzyme that plays a critical role in DNA replication by synthesizing new DNA strands from nucleotides and is also involved in the repair of DNA. This enzyme removes RNA primers from the Okazaki fragments on the lagging strand and fills in the resulting gaps with DNA nucleotides, ensuring that the newly formed DNA is complete and accurate. Its activities are essential for maintaining genomic integrity during cell division.

5 Must Know Facts For Your Next Test

1. DNA polymerase I has both 5' to 3' polymerase activity for adding nucleotides and 3' to 5' exonuclease activity for proofreading and correcting errors.
2. This enzyme is particularly important in prokaryotic cells, where it aids in DNA replication and repair mechanisms.
3. DNA polymerase I has a lower processivity compared to other DNA polymerases, meaning it adds fewer nucleotides before releasing the template strand.
4. It works primarily on the lagging strand to remove RNA primers laid down by primase and replaces them with DNA nucleotides.
5. In E. coli, DNA polymerase I is encoded by the polA gene, and its activity can be affected by environmental factors like temperature and pH.

Review Questions

• How does DNA polymerase I contribute to the process of DNA replication, particularly regarding Okazaki fragments?
  • DNA polymerase I is essential for processing Okazaki fragments on the lagging strand during DNA replication. It removes the RNA primers that are initially laid down to initiate fragment synthesis and subsequently fills in the gaps with DNA nucleotides. This action ensures that each segment of the lagging strand is fully constructed, leading to a complete and continuous DNA molecule.
• Discuss the proofreading abilities of DNA polymerase I and why they are vital for cellular function.
  • DNA polymerase I possesses 3' to 5' exonuclease activity, which allows it to proofread newly synthesized DNA. This means it can identify and remove incorrectly paired nucleotides during replication. Such proofreading is crucial for minimizing mutations, thereby maintaining genomic stability and preventing errors that could lead to cell malfunction or disease.
• Evaluate the significance of DNA polymerase I's lower processivity in the context of its role in prokaryotic cells during DNA replication.
  • The lower processivity of DNA polymerase I means that it does not remain attached to the DNA template as long as more processive enzymes. This characteristic is significant in prokaryotic cells because it allows DNA polymerase I to effectively remove RNA primers and replace them with DNA in a timely manner without stalling replication. While this may appear less efficient than other enzymes, its specific role is essential for ensuring that both leading and lagging strands are completed accurately, emphasizing a collaborative effort with other polymerases during the replication process.

Related terms

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

Leading Strand: The continuous strand of DNA that is synthesized in the same direction as the replication fork, allowing for uninterrupted replication.

DNA Ligase: An enzyme that facilitates the joining of Okazaki fragments by forming phosphodiester bonds between adjacent nucleotides.