The genomic DNA of humans is densely packed without knots into individual cells via fractal globule architecture.

“‘We’ve long known that on a small scale, DNA is a double But if the double
helix didn’t fold further, the genome in each cell would be two meters
long. Scientists have not really understood how the double helix folds
to fit into the nucleus of a human cell, which is only about a hundredth
of a millimeter in diameter…’

“The researchers report two striking findings. First, the human genome is
organized into two separate compartments, keeping active genes separate
and accessible while sequestering unused DNA in a denser storage
compartment. Chromosomes snake in and out of the two compartments
repeatedly as their DNA alternates between active, gene-rich and
inactive, gene-poor stretches….

“Second, at a finer scale, the genome adopts an unusual organization
known in mathematics as a ‘fractal.’ The specific architecture the
scientists found, called a ‘fractal globule,’ enables the cell to pack
DNA incredibly tightly — the information density in the nucleus is
trillions of times higher than on a computer chip — while avoiding the
knots and tangles that might interfere with the cell’s ability to read
its own genome. Moreover, the DNA can easily unfold and refold during
gene activation, gene repression, and cell replication.” (EurekAlert! 2009)

“We identified an additional level of genome organization that is characterized by the spatial segregation of open and closed chromatin to form two genome-wide compartments. At the megabase scale, the chromatin conformation is consistent with a fractal globule, a knot-free, conformation that enables maximally dense packing while preserving the ability to easily fold and unfold any genomic locus. The fractal globule is distinct from the more commonly used globular equilibrium model.” (Lieberman-Aiden et al. 2009:289);326/5950/289

Last Updated September 14, 2016