This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Replication, Subject name: Biochemistry
During unwinding of DNA, relief of supercoil is made possible by 
Select and explain. 
A. Topoisomerase, B. Gyrase, C. Helicase, D. Polymerase
A: Topoisomerase
Answer: A: Topoisomerase 
Explanation: During unwinding of DNA, relief of supercoil is made possible by Topoisomerase DNA helicase unwinds the DNA without cutting but using energy from hydrolysis of ATP. Gyrase is a bacterial type II topoisomerase which acts on closed circular DNA (bacteria have circular DNA).