Monday, December 10, 2012

The body's response to fasting, part 3: histones and protein modifications

I apologize for not sticking to my schedule of posting. I had a horrible week last week, health-wise. Fortunately, I'm feeling much better now. And what better way to celebrate getting out of that slump than a nice session of writing? Yay!

So, back to biology. As you are all probably aware, the information a cell needs to carry out all it's functions is stored in the biopolymer DNA. Apart from its information storage capabilities, we must also consider the physical reality of a DNA molecule. For example, a human cell has about 2 meters of DNA in its nucleus, while the average human cell is hundredths of a millimeter in diameter. This would be an impossible situation if the DNA didn't fit into the nucleus in a highly organized manner - and you thought packing your car for a road trip was hard!

This organization is accomplished by - big surprise - proteins! Among these proteins that control the physical organization of DNA are the histones. Basically, they're little balls of protein that the DNA wraps around to keep it neat and tidy. Now, here's the interesting bit: this physical organization of the DNA has implications for its function as a carrier of information. The stronger the interaction between a segment of DNA and a histone, the less accessible the DNA is to the machinery of gene expression.

To understand how the interaction between a histone and a length of DNA is controlled, we need to go into one method of changing protein behavior that I have been saving for last. In addition to all the things I've brought up in the last two posts, proteins can also undergo chemical reactions that change their molecular makeup and thus their behavior. These are called post-translational modifications, and they are often employed with histones to modify their affinity for DNA. One common modification that is made to histones is acetylation, which decreases the histone's affinity for DNA and leaves the DNA more available for transcription. Deacetylation has the opposite effect. Additionally, other protein's behaviors are modified by acetylation and deacetyation.

So, now that that's out of the way, I think I'm finally ready to talk about fasting. And after all this build-up, I hope it turns out to be worth it.

Next post (if all goes well): Monday, December 17