DNA, RNA, Chromosomes, and Genes


What is DNA supercoiling?

When DNA is not being replicated or specific genes are not transcribed, its normal form is two strands twisted around a helical axis, much like a spiral staircase turning clockwise. However, during DNA replication or transcription, enzymes alter the structure of DNA such that additional twists are added (positive supercoiling) or subtracted (negative supercoiling). Either type of supercoiling makes DNA even more compact. A group of enzymes, the topoisomerases, are able to disentangle DNA strands; they are called topoisomerases because they control the topology of DNA.


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