AP BIOLOGY

Detailed explanation-1: -The topoisomerases relax the torsional strain by nicking the phosphate backbone of either one or both the DNA strands. Therefore, these enzymes play vital roles during cell division through regulation of DNA supercoiling.

Detailed explanation-2: -Abstract. DNA topoisomerase I enzymes relieve the torsional strain in DNA; they are essential for fundamental molecular processes such as DNA replication, transcription, recombination, and chromosome condensation; and act by cleaving and then religating DNA strands.

Detailed explanation-3: -DNA supercoiling plays an important role in replication, repair, recombination, transposition and transcription. DNA topoisomerases type I are ATP-independent enzymes that cut one DNA strand and relax supercoiled molecules. DNA topoisomerases type II requiere ATP, cut both DNA strands and supercoil relaxed molecules.

Detailed explanation-4: -Type II topoisomerases are involved in both decatenation of daughter chromosomes, and relieving the positive supercoiling ahead of the replication fork.

Detailed explanation-5: -Two DNA topoisomerases control the level of negative supercoiling in bacterial cells. DNA gyrase introduces supercoils, and DNA topoisomerase I prevents supercoiling from reaching unacceptably high levels.