Dna polymerase

Definition

DNA polymerase is an enzyme that synthesizes new DNA strands by adding nucleotides to a pre-existing chain during DNA replication. It plays a crucial role in ensuring accurate duplication of the genetic material, as it not only catalyzes the polymerization process but also possesses proofreading capabilities to maintain fidelity in DNA synthesis.

5 Must Know Facts For Your Next Test

1. There are several types of DNA polymerases, with DNA polymerase III being the primary enzyme responsible for DNA replication in prokaryotes.
2. DNA polymerases require a primer to initiate synthesis since they cannot start a new strand from scratch; this primer is usually made of RNA.
3. The proofreading activity of DNA polymerase occurs due to its 3' to 5' exonuclease activity, which allows it to remove incorrectly paired nucleotides.
4. In eukaryotes, multiple DNA polymerases exist (e.g., DNA polymerase α, β, δ, and ε), each with specific roles during replication and repair processes.
5. DNA polymerase can only add nucleotides to the 3' end of a growing DNA strand, which means replication occurs in a 5' to 3' direction.

Review Questions

• How does DNA polymerase contribute to the accuracy of DNA replication?
  • DNA polymerase enhances the accuracy of DNA replication through its proofreading ability. It has 3' to 5' exonuclease activity that enables it to identify and remove incorrectly incorporated nucleotides immediately after they are added. This process significantly reduces the rate of mutations by ensuring that only correctly matched nucleotides remain in the new DNA strand.
• Compare and contrast the roles of different types of DNA polymerases in prokaryotic and eukaryotic cells.
  • In prokaryotic cells, DNA polymerase III is primarily responsible for synthesizing the new DNA strand during replication, while DNA polymerase I is involved in removing RNA primers and filling in gaps with DNA. In eukaryotic cells, several DNA polymerases exist with specialized functions; for example, DNA polymerase α starts the synthesis by laying down RNA primers, while DNA polymerase δ and ε are key players in elongating the leading and lagging strands. This diversity reflects the more complex cellular organization and replication mechanisms in eukaryotes compared to prokaryotes.
• Evaluate the implications of malfunctioning DNA polymerases on genetic stability and disease development.
  • Malfunctioning DNA polymerases can lead to increased mutation rates due to errors during DNA replication and inadequate proofreading. Such mutations can compromise genetic stability, potentially resulting in genomic instability associated with various diseases, including cancer. The inability to accurately replicate or repair damaged DNA can lead to uncontrolled cell growth and proliferation, highlighting the critical role that functioning DNA polymerases play in maintaining genomic integrity and preventing disease.

Related terms

Nucleotide: The basic building block of DNA and RNA, consisting of a sugar, a phosphate group, and a nitrogenous base.

Leading Strand: The continuously synthesized strand of DNA during replication that runs in the 5' to 3' direction towards the replication fork.

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