Which of the following statements about type I topoisomerases is FALSE? They can
ID: 81329 • Letter: W
Question
Which of the following statements about type I topoisomerases is FALSE?
They can only decrease writhe (W) and therefore, they can only reduce the linking number of DNA.
During the reaction mechanism, type I topoisomerases switch between closed and open conformations.
Type I topoisomerases are found in both prokaryotes and eukaryotes.
Their reaction mechanism involves nucleophilic attack by an active site tyrosine residue at a phosphate group in a phosphodiester bond.
They can only decrease writhe (W) and therefore, they can only reduce the linking number of DNA.
Explanation / Answer
Correct answer: A) They can only decrease writhe (W) and therefore, they can only reduce the linking number of DNA.
Explanation: Type I topoisomerases are enzymes that helps to remove or cut one among the two strands of the double-stranded DNA, thus relaxing and re-aligning them. Therefore, type I topoisomerases only changes (and does not reduce) the linking number of the circular DNA strands by unit of 1 or multiples of one.
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