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If a DNA segment under twist strain is closed into a circle by joining its two ends, and then allowed to move freely, it takes on different shape, such as a figure-eight. This shape is referred to as a supercoil. (The noun form "supercoil" is often used when describing DNA topology.) The DNA of most organisms is usually negatively supercoiled.
Where DNA gyrase forms a tetramer and is capable of cleaving a double-stranded region of DNA, reverse gyrase can only cleave single stranded DNA. [ 3 ] [ 4 ] More specifically, reverse gyrase is a member of the type IA topoisomerase class; along with the ability to relax negatively or positively supercoiled DNA [ 5 ] (which does not require ATP ...
Contrary to intuition, a topological property, the linking number, arises from the geometric properties twist and writhe according to the following relationship: L k = T + W, where L k is the linking number, W is the writhe and T is the twist of the coil. The linking number refers to the number of times that one strand wraps around the other.
DNA gyrase, or simply gyrase, is an enzyme within the class of topoisomerase and is a subclass of Type II topoisomerases [1] that reduces topological strain in an ATP dependent manner while double-stranded DNA is being unwound by elongating RNA-polymerase [2] or by helicase in front of the progressing replication fork.
DNA in cells is negatively supercoiled and has the tendency to unwind. Hence the separation of strands is easier in negatively supercoiled DNA than in relaxed DNA. The two components of supercoiled DNA are solenoid and plectonemic. The plectonemic supercoil is found in prokaryotes, while the solenoidal supercoiling is mostly seen in eukaryotes.
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After introducing a nick in the system, the negative supercoil gradually unwinds (c) until it reaches its final, circular, plasmid state (d). [2] Nicked DNA can be the result of DNA damage or purposeful, regulated biomolecular reactions carried out in the cell. During processing, DNA can be nicked by physical shearing, over-drying, or enzymes.
Seoul (Reuters) -Investigators found bird feathers and blood in both engines of the Jeju Air jet that crashed in South Korea last month, killing 179 people, a person familiar with the probe told ...