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Chapter 28: Problem 7

How do DNA gyrases and helicases differ in their respective functions and modes of action?

Short Answer

Expert verified
DNA gyrase and DNA helicase are both crucial for DNA replication. However, the gyrase works by changing DNA's physical properties to protect it from damage. It does this through introducing negative supercoils. On the other hand, helicase unravels the double helix by breaking the bonds between the base pairs, creating a replication fork.

Step by step solution

01

Define DNA Gyrase and its functions

DNA gyrase is an enzyme within the class of topoisomerases. It introduces negative supercoiling into DNA strands by breaking the DNA molecule's phosphate backbone, and is crucial in replication as it relieves strain while the DNA is being unwound by other enzymes.
02

Define DNA Helicase and its functions

DNA helicase is also an enzyme that plays a vital role in DNA replication. It separates or unwinds the two strands of the DNA double helix by breaking the hydrogen bonds between the complementary base pairs. This leaves the two single strands available for replication.
03

Discuss the differences

While both enzymes assist in DNA replication, they have different roles and modes of action. DNA Gyrase alters the physical properties of DNA, relieving strain and preventing DNA damage while helicase separates the two DNA strands creating a replication fork that allows other enzymes to synthesize a new strand. In terms of action, DNA gyrase achieves its function by introducing negative supercoils to the DNA while helicase breaks the hydrogen bonds holding the base pairs together. Thus, their main difference lies in their functions and how they accomplish those functions.

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Most popular questions from this chapter

(a) What are the respective roles of the 5 '-exonuclease and \(3^{\prime}\) exonuclease activities of DNA polymerase I? (b) What might be a feature of an \(E .\) coli strain that lacked DNA polymerase I 3 '-exonuclease activity?

The eukaryotic translesion DNA polymerases fall into the Y family of DNA polymerases. Structural studies reveal that their fingers and thumb domains are small and stubby (see Figure 28.10 ). In addition, Y-family polymerase active sites are more open and less constrained where base pairing leads to selection of a dNTP substrate for the polymerase reaction. Discuss the relevance of these structural differences. Would you expect Y-family polymerases to have \(3^{\prime}\) -exonuclease activity? Explain your answer.

Transposons are mutagenic agents. Why?

Homologous recombination in \(E .\) coli leads to the formation of regions of heteroduplex DNA. By definition, such regions contain mismatched bases. Why doesn't the mismatch repair system of \(E .\) coli eliminate these mismatches?

Asako Furukohri, Myron F. Goodman, and Hisaji Maki wanted to discover how the translesion DNA polymerase IV takes over from DNA polymerase III at a stalled replication fork (see Journal of Biological Chemistry \(283: 11260-11269,2008\) ). They showed that DNA polymerase IV could displace DNA polymerase III from a stalled replication fork formed in an in vitro system containing DNA, DNA polymerase III, the \(\beta\) -clamp, and SSB. Devise your own experiment to show how such displacement might be demonstrated. (Hint: Assume that you have protein identification tools that allow you to distinguish easily between DNA polymerase III and DNA polymerase IV.
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