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Chapter 20: Problem 18

Why are two different DNA polymerase enzymes required to replicate the E. coli chromosome?

Short Answer

Expert verified
Two different DNA polymerase enzymes, DNA Polymerase I and III, are required in E. coli chromosome replication due the distinct roles they play. DNA Polymerase III is responsible for adding nucleotides in both leading and lagging strands. DNA Polymerase I, on the other hand, replaces RNA primers with DNA and ensures the correction of any errors in the newly synthesized DNA.

Step by step solution

01

Introduction of DNA Replication in E. coli

The E. coli's chromosome replication begins at a specific location known as the origin of replication or OriC. The replication proceeds in both directions around the circular DNA molecule and this process termed as a bidirectional mechanism. The key enzymes involved in DNA replication are Helicase, topoisomerase, primase, DNA polymerase I and III and ligase.
02

Role of DNA Polymerase III

The primary function of DNA polymerase III in E. coli during replication is to add deoxyribonucleotides (nucleotides that construct DNA) in a 5' to 3' direction on the leading and lagging strands of DNA. It has proofreading capabilities to delete any mismatched bases. It provides the primary polymerization activity, synthesizing both the leading and lagging strands virtually.
03

Role of DNA Polymerase I

DNA polymerase I plays an essential role in replication mainly for replacing RNA primers with DNA. It also acts on Okazaki fragments in the lagging strand where it removes the RNA primer created by primase and replaces it with DNA. This enzyme takes care of connecting the Okazaki fragments on the lagging strand to complete the replication process.
04

Why Are Both Needed?

So, both enzymes are required for DNA replication because each has a distinct function. DNA polymerase III is crucial for the main replication process, both on leading and lagging strands. DNA Polymerase I, on the other hand, is essential for replacing the RNA primers with DNA and repairing any errors in newly synthesized DNA.

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Most popular questions from this chapter

Ethyl methane sulfonate (EMS) is a reactive alkylating agent that ethylates the O-6 residue of guanine in DNA. If this modified \(\mathrm{G}\) is not excised and replaced with a normal \(\mathrm{G}\), what would be the outcome of one round of DNA replication?

Explain why uracil \(N\)-glycosylase cannot repair the damage when 5 -methylcytosine is deaminated to thymine.

Damage to a single strand of DNA is readily repaired through a variety of mechanisms, while damage to bases on both strands of DNA is more difficult for the cell to repair. Explain.

Will DNA repair in \(E\). coli be dependent on the enzymatic cofactor \(\mathrm{NAD}^{\oplus}\) ?

Explain why the overall error rate for DNA replication in E. coli is approximately \(10^{-9}\), although the rate of misincorporation by the replisome is about \(10^{-5}\).
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