 different chromosomes.” And within individual chromosomes, “open [active] chromatin interacts more with open chromatin and closed with closed,” wrote Aiden. In short: Genes have more interactions with regions on their own chromosome; and within any given chromosome, active regions group together with other active regions, while quiet or gene-poor areas group with other quiet regions.
Aiden had found a paper theorizing that long polymers – DNA is a good example – are able to form very tight coils with no knots, “a configuration known as the fractal globule.” One of the most striking characteristics of the fractal globule is that it can be folded and refolded without disturbing the rest of the condensed polymer.
The fractal globule is easy to explain to graduate students because it closely resembles the only food we can afford: ramen, said Aiden.
Uncooked, the noodles don’t contain any knots. Even when partially cooked, they don’t get tangled in the cooking pan. However, ramen noodles do become tangled after cooking, whereas chromatin stably maintains its unknotted state throughout interphase – the period between cell divisions when chromatin in the nucleus uncoils. In that condensed but non-knotted configuration, sections of chromatin that are far apart on the long strands may be brought into proximity. Thus, interactions between chromatin on the same chromosome, or between sections with similar properties or functions, are made possible by the way chromatin is organized in the interphase nucleus.
These are but a few of the innovative and complex understandings that inspired the creators of the Genome Ball (for more information about the 3-D printing of the Genome Ball displayed at the exhibition, see the feature article “Super 3D Model: How the Genome Ball Was Created” on this website). Our knowledge of the nucleus has come a long way in the 332 years since Leeuwenhoek. But, as Aiden’s Science essay concluded: “at the fringes of our maps the world is full of surprises.”
The same is certainly true of the nucleus.
Source: Unlockinglifescode.org/the-genome-ball. Access November 19, 2017, Genome Project NIH
(1) “Zoom!” Science 334 (2 December 2011): 1222-1223.
(2) “DNA packaging: Nucleosomes and Chromatin.” Nature Education 1 (2008):26.
(3) “Regulatory and Epigenetic Landscapes of Mammalian Genomes,” Current Topics in Genome Analysis 2014. March 26, 2014.
(4) “Leeuwenhoek Sees the Cell Nucleus.” Science of Aging: Timeline of Discoveries.
(5) Comprehensive Mapping of Long-Range Interactions Reveals Folding Principles of the Human Genome. Science 326 (9 October 2009): 189-324.