Question

DNA gyrase can

• A. cut single-stranded DNA
• B. relax supercoiled DNA
• C. introduce negative supercoiling in DNA
• D. not utilize ATP

Answer 1

The Correct Option is C

DNA gyrase is an essential enzyme in bacteria that is involved in the manipulation of DNA topology, mainly through the process of supercoiling. Let's analyze why the correct answer is "introduce negative supercoiling in DNA."

1. Understanding Supercoiling:
   • DNA supercoiling refers to the overwinding or underwinding of DNA strands and is a crucial aspect of DNA functionality because it affects the compactness and the ability of DNA to interact with other molecules.
   • There are two types of supercoiling: positive and negative. Positive supercoiling occurs when DNA is wound more tightly than normal, while negative supercoiling occurs when it is wound less tightly.
2. Role of DNA Gyrase:
   • DNA gyrase is a type II topoisomerase enzyme found in bacteria and plants. It is unique because it introduces negative supercoiling into the DNA, using energy derived from ATP hydrolysis. This adds torsional stress, which is crucial for replication and transcription processes.
3. Justification of Options:
   • 1. Cut single-stranded DNA: DNA gyrase acts on double-stranded DNA rather than single strands, making this option incorrect.
   • 2. Relax supercoiled DNA: Although some topoisomerases can relax supercoiled DNA, DNA gyrase primarily introduces, rather than reduces, supercoiling.
   • 3. Introduce negative supercoiling in DNA: As explained, DNA gyrase specifically introduces negative supercoils, making this the correct answer.
   • 4. Not utilize ATP: DNA gyrase actually requires ATP to function, as this energy is crucial for altering DNA topology.

The correct answer is "introduce negative supercoiling in DNA". This function helps in the compaction of the bacterial genome and facilitates processes like DNA replication and transcription.