DNA Globules

Left: a tangled equilibrium globule. Right: a fractal globule. Similar colors represent nearby regions in the DNA strand. Simulations by Leonid Mirny and Maxim Imakaev.
Unwound into a linear strand, our DNA would stretch to nearly two meters.
The difficult task of folding this DNA into the cell nucleus, which has a diameter of about 5 millionths of a meter, is accomplished by histones, protein components of chromatin.
The equilibrium globule (left) folds DNA but introduces tangles and knots, making it difficult for DNA to unfold and refold during replication, and gene activation and repression.
Alexander Grosberg's fractal globule (right) folds the DNA recursively, the same folding pattern repeated over many levels. This folds without knots, avoiding the problems of the equilibrium globule.
Recent experiments support the fractal globule hypothesis.

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