DNA supercoil

Supercoiled DNA is a synonym of closed circular ( cccDNA ), as well as linear DNA molecules which are packaged as extremely spiraled helices equivalent present in the core ( in prokaryotes ) or in the nucleus ( in eukaryotes ).

Geometric still sits a dimension Spiralisation on the spiral, which is also practically demonstrated. Naturally occurring circular DNA molecules are present in the supercoiled form. Superhelikalität caused by the introduction of the helical turns. The twist of the DNA is compensated by formation of a supercoiled structure. Since the total length of the DNA of a cell is often a thousand times the diameter of the cell, the supercoiling is essential for the functioning of several organisms.

A right-handed twist is referred to as negative supercoiling (also negative supertwist ), a left-handed supercoiling as a positive supercoiling (also positive super-twist ).

Structure

Supercoiled DNA is found in every living cell. It ensures that there is always a minimum amount of base pairs is opened so as to allow the polymerases to supplement the template strand to the new double strand. This is true for the replication and transcription. It comes to a balance between the two so-called topoisomerases.

Topoisomerase II cuts two strands and glues them. This process consumes energy and is therefore dependent on ATP.

The topoisomerase I does not consume energy and removes the " supercoiled " by cuts only one strand rotates around the closed string and the gap closes again. So can run the DNA and RNA synthesis only when sufficient ATP is present. Under starvation conditions there will be no synthesis.

The gyrase inhibitors, which inhibit the prokaryotic topoisomerase II ( gyrase ) and in part IV include, for prokaryotes to the most powerful known toxins; Examples are the nalidixic acid or fluoroquinolones.