Figure 4.6. Covalently closed circular (CCC) DNA and DNA supercoiling.

Figure 4.6Covalently closed circular (CCC) DNA and DNA supercoiling

The double-stranded CCC DNA is shown on left in schematic form (no attempt is made to show the double helical structure). Unless one of the two DNA strands becomes nicked, the twisting of the double helix cannot be relaxed and the tension induced causes spontaneous formation of a supercoiled structure shown on the right. Nicking of either DNA strand, however, relieves the tension by permitting rotation at the free end.

From: Chapter 4, Cell-based DNA cloning

Cover of Human Molecular Genetics
Human Molecular Genetics. 2nd edition.
Strachan T, Read AP.
New York: Wiley-Liss; 1999.
Copyright © 1999, Garland Science.

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