Tuesday, November 27, 2012

The body's response to fasting, part 2: gene expression

Since I haven't gotten any input to do something else, I'm going to stick with my plan to write about gene expression today.

The very quick, simple explanation for how gene expression works is that a sequence of DNA is transcribed into a sequence of RNA, and that in turn is translated into a sequence of amino acids - a protein! But it's the details of that scheme that make it such an interesting process. To begin with, what does the transcribing? RNA polymerase - another protein! As I mentioned last time, the behavior of proteins is controlled by the other molecules they interact with. This is especially important for RNA polymerase, because if it didn't have controls, it would just transcribe as much of one chromosome as it could before dissociating, and what use would that be to anyone? It would be chaos. This is prevented by the fact that RNA polymerase can't attach to DNA and start the transcription process by itself. It needs the assistance of other proteins, called transcription factors.

 What makes this whole thing work is that DNA is not just a sequence of symbols, as you've often seen it characterized. DNA is a long molecule with it's own physical properties, and different sequences of DNA have different physical properties. One of those physical properties is affinity for proteins like transcription factors. So a gene consists of the sequence that is transcribed into messenger RNA and a sequence with an affinity for certain transcription factors, which in turn assist or hinder RNA polymerase with beginning the transcription process.

Like most proteins, transcription factors are themselves very sensitive to their environment. Aside from only having an affinity for specific sequences of DNA, their affinity for those sequences is also increased or decreased by interaction with other molecules in the cell. Certain cellular conditions change the affinity of transcription factors for their regulatory sequences of DNA, and that in turn changes which genes are being transcribed into proteins. This change in gene expression can in turn change the cellular conditions, and the whole regulatory process continues. This means that your body is constantly changing its chemical makeup in response to its current situation. I find that very exciting.

My plan for next time, unless I get suggestions to do something else, is to get into some more advanced protein and gene regulation. It's all completely necessary, I assure you.

I also realize that most people don't consider Wikipedia to be a serious reference. While that may be true, it is a great place for people with a variety of backgrounds to get a lot of basic information on a topic. So please don't think less of me for referring my readers to Wikipedia for additional information on these topics.

Next post: Tuesday, December 4