Question

Summarize and compare the properties of DNA polymerase I, II, and III.

Short answer

Question: Briefly compare the functions and properties of DNA polymerase I, II, and III in prokaryotic DNA replication and repair. Answer: DNA polymerase I is primarily responsible for removing RNA primers and replacing them with DNA fragments on the lagging strand during DNA replication, and it has high exonuclease activity for proofreading and gap-filling. DNA polymerase II is mainly involved in DNA repair, especially under oxidative stress, and it can bypass DNA damage, contributing to error-prone DNA synthesis. It also possesses 3' to 5' exonuclease activity for proofreading. DNA polymerase III is the primary enzyme in prokaryotic DNA replication, operating on both leading and lagging strands with high processivity and 3' to 5' exonuclease activity for proofreading, ensuring high fidelity.

Step-by-step solution

Understanding DNA Polymerases

DNA polymerases are enzymes that play a critical role in DNA replication and repair in living organisms. Specifically, they catalyze the synthesis of new DNA strands by adding nucleotide bases to a growing DNA chain. Three main types of DNA polymerases are implicated in this process in prokaryotes: DNA polymerase I, II, and III. While they all share the general features of DNA polymerases, each enzyme has unique characteristics.

DNA Polymerase I

DNA polymerase I plays a role in DNA replication, repair, and recombination. Its primary function is to remove RNA primers from the lagging strand of DNA during DNA replication and replace them with new DNA fragments. Furthermore, DNA polymerase I has a high exonuclease activity, which allows it to proofread and correct errors made during DNA replication. Its 3’ to 5’ exonuclease activity is responsible for proofreading, whereas its 5’ to 3’ exonuclease activity fills in the gaps with DNA fragments.

DNA Polymerase II

DNA polymerase II is primarily involved in DNA repair and participates in the process called replication restart. This enzyme's most notable attribute is its ability to bypass DNA damage during DNA replication and repair processes, thus bestowing it with error-prone DNA synthesis property. DNA polymerase II is involved in DNA replication under specific conditions, such as oxidative stress. It also possesses 3’ to 5’ exonuclease activity, which allows for proofreading and error correction.

DNA Polymerase III

DNA polymerase III is the primary enzyme involved in the replication of prokaryotic DNA. It is considered to be the primary holoenzyme of DNA replication, consisting of multiple subunits and playing a central role in initiating and elongating new DNA strands. DNA polymerase III has a high processivity and operates on both leading and lagging DNA strands during replication. It also boasts high fidelity due to its 3’ to 5’ exonuclease activity, which enables it to proofread and correct errors efficiently.

Comparison of DNA Polymerase I, II, and III

In summary, DNA polymerase I, II, and III all contribute to DNA replication and repair in prokaryotes. Each enzyme has distinct functions and properties as follows: 1. DNA polymerase I is primarily responsible for removing RNA primers and replacing them with DNA fragments on the lagging strand during DNA replication. It has high exonuclease activity for both proofreading and gap-filling. 2. DNA polymerase II's primary role is in DNA repair, particularly under conditions of oxidative stress. It is capable of bypassing DNA damage, contributing to error-prone DNA synthesis. It also possesses 3' to 5' exonuclease activity for proofreading. 3. DNA polymerase III is the main holoenzyme involved in DNA replication in prokaryotes. It is highly processive, operates on both leading and lagging strands, and has 3' to 5' exonuclease activity for proofreading, thus ensuring high fidelity. By understanding and comparing their unique properties, one can appreciate how these distinct enzymes contribute to the maintenance and propagation of genetic information within living organisms.