Base Unpaired Regions in Supercoiled Replicative Form DNA of Jbc

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in a remarkable experiment a cell of E coli was lysed releasing its chromosome four electron microscopy what spewed out of this single cell was a strand of DNA 1,500 times longer than ecoli itself how could this enormous molecule fit into a single cell inside a bacterial cell the DNA is much more tidy the DNA is compacted into a structure called a nucleoid a nucleoid consists of DNA arranged in tightly wound loops with the boundaries of the loop domains defined by histone like anchoring proteins the DNA in the loops is super coiled that is the double helix of DNA coils upon itself creating a tighter more compact structure if one of the strands of a double helix is cut the DNA loses its super coils as the tension dissipates however the other domains remain super coiled because they are constrained at their bases by the anchoring proteins which prevent rotation to understand supercoiling consider a completely relaxed circular piece of DNA an unstressed DNA molecule naturally forms a heli