Thursday, December 5, 2013

RIPE: More Polymer Entanglements

In a previous post I discussed entanglements in polymer melts. I thought I’d spend sometime discussing some “practical” matters in which entanglements play a role. Today, lets focus on a very special kind of polymer: DNA.

You have a lot of DNA in your body. In fact, each cell in your body has over 2 meters of DNA packed inside a small bag called the nucleus. The diameter of a typical nucleus is less than 10 microns.

If that hasn’t knocked you off of your seat yet, let me put it in perspective. If all the DNA in your body were set end to end, it would stretch from the Sun to Pluto!

To freaking Pluto; which they say is not even a planet anymore!

I have trouble dealing with headphones in my pocket, and the nucleus manages to pack and use all of that DNA inside it. How the heck does it do that?

The answer turns out to have some parallels in everyday life. How do you deal with a really long water hose or vacuum cleaner cable? You roll it around something! You organize it!

Thus, DNA is not packed randomly. It is organized in a very sophisticated hierarchical manner. This allows the nucleus to sequester a lot of material and information in a very small compartment. Here is a nice video that explains this organization (DNA - nucleosomes - chromatin).

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