AP BIOLOGY

Detailed explanation-1: -Topoisomerase prevents the over-winding of the DNA double helix ahead of the replication fork as the DNA is opening up; it does so by causing temporary nicks in the DNA helix and then resealing it. As synthesis proceeds, the RNA primers are replaced by DNA.

Detailed explanation-2: -The enzyme responsible for preventing the over-winding of DNA is topoisomerase. Topoisomerase is an enzyme that relieves the overtwisting and strain of DNA ahead of the replication fork.

Detailed explanation-3: -Topoisomerase I is proposed to work ahead of the replication fork to remove positive DNA supercoils, whereas topoisomerase II is proposed to work primarily behind the fork to remove precatenanes. In contrast to replication models, drug models place topoisomerase II ahead of DNA tracking systems.

Detailed explanation-4: -Topoisomerases play critical roles in DNA replication, transcription, and chromosome structure by altering the topological state of DNA, . These enzymes are capable of relaxing supercoiled DNA and of decatenating interlocked DNA (Fig.

Detailed explanation-5: -DNA topoisomerases solve the topological problems associated with DNA replication, transcription, recombination, and chromatin remodeling by introducing temporary single-or double-strand breaks in the DNA.