Action of DNA Gyrase

Why is DNA coiled in multiple directions during supercoiling? Supercoiling simply means the coiling of an already coiled structure (such as DNA). DNA is coiled around itself for several reasons. The three dimensional structure of DNA affects its function. The coiling can have positive or negative effects on gene expression. Also, the unraveling of portions of a circular bacterial chromosome during transcription could induce coiling that could prevent the strands for reattaching to one another. Supercoiling in the opposite direction will cancel out coiling problems during transcription. Coiling DNA in multiple directions reduces the space occupied by DNA and makes the structure more stable during replication and transcription.

View the animation below, then complete the quiz to test your knowledge of the concept.


1	DNA gyrase introduces ______ supercoils in the DNA

		A)	positive
		B)	negative
		C)	neutral
		D)	all of the above

2	________ supercoiling represents a force on the DNA in a right-handed direction.

		A)	Negative
		B)	Positive
		C)	Neutral
		D)	Detrimental

3	DNA gyrase uses ________ to alleviate supercoiling.

		A)	spare nucleotides
		B)	mutations
		C)	topoisomerase II
		D)	ATP

4	DNA gyrase adds positive supercoils to a negatively coiled DNA molecule.

		A)	True
		B)	False

5	Positive supercoiling causes the DNA to form a more compact structure.

		A)	True
		B)	False

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