DNA-supercoiling occurs because of the following phenomena:
I. Topoisomerases either add to or subtract from DNA-twists.
II. Helicases cause strain when separating the two DNA-single strands that form a DNA double-helix.
III. DNA-double strands are densely packed within chromosomes. Therefore, the twist imposed on one DNA-double strand can cause cooperative supercoiling of the neighboring strands.
IV. RNA-polymerases, the group of enzymes responsible for RNA-transcription can cause supercoiling.

Question

Quizplus · Accepted Answer

All four phenomena listed can contribute to DNA supercoiling. Topoisomerases can add or subtract DNA twists to create supercoiling, helicases can cause strain when separating DNA strands, tightly packed DNA double strands can create cooperative supercoiling, and RNA polymerases can induce supercoiling as they transcribe DNA. Therefore, all of the options listed in the answer choice are correct.

DNA-Supercoiling Occurs Because of the Following Phenomena