What happened to the cat with dry skin? Purrrrritus.

I've often wondered why we scratch itches. If you think about it from an objective point of view, it doesn't make any sense to scratch. If anything, it only irritates the skin more. So why does it feel good? Thankfully, the back page of Scientific American, bringer of useless yet fascinating information, had a short article explaining it. Turns out that the "pruritus" (note quotation marks for fancy Latin name for itching) neurons are separate from "pain" and "rubbing" (note quotation marks for non-fancy non-Latin names for pain and rubbing) neurons. Because of a local inhibitory effect, these neurons trump the pruritus sensors, temporarily relieving the itching sensation. The itching arises in the first place from things like dryness and chemical irritation.

Maybe it could work the other way. We could be treating soreness and pain with poison ivy, or something, if the pruritus sensory neurons can also inhibit the pain ones.

Also, "pruritus" is an incredibly tough word to pronounce. It's like "rural," but harder. I can only imagine trying to say it in French; I think I'd need some Halls afterwards.

More on the origins of life.

Yesterday, I read a fantastic article in Scientific American about the chemical origins of life. It started off with a review of the RNA world hypothesis, which essentially postulates that life began by the chance formation of a catalytic RNA molecule which had the ability to self-replicate. At this point, however, it has become obvious that the odds of that happening are so extraordinarily astronomical that it's almost certain that something else came first. Even in the famous Stanley Miller experiment, there were only amino acids formed; no sugars or bases. In addition, ribose has proved nearly impossible to synthesize under the prebiotic chemical conditions.

This all led to the metabolism-first hypothesis, the main subject of the article. It's a lot more general than the RNA-first hypothesis, and requires much smaller molecules. What it boils down to is an energetically downhill redox reaction of a mineral fuelling an uphill organic reaction, say A to B. A is eventually regenerated by a stepwise series of exergonic reactions; in other words, a rudimentary cycle. The hypothesis then says that chemical and physical interference with the reactions would cause them to find alternative routes to get back to A, forming more complex networks, and the opportunity to form catalysts. The author goes as far as saying that nucleotides originated as some form of catalyst or energy-producing reaction (after all, ATP is a pretty universal energy-storing compound). The jump to RNA would be made by the chance polymerization of nucleotides, something far far more likely than a de novo formation. And now we've got to the RNA world.

The argument that the article seems to have the most trouble dealing with is how this system of reactions stores information. The author suggests that the chemicals themselves store it in a "compositional genome," which is replicated by the diffusion of chemicals from one physical compartment to another. This theory leaves open the possibility of something like a chemical founder effect - a drastic change in concentration occurs, and a new network is formed. This would in turn allow for the selection of some chemical systems that are better able to grow in concentration than others, and there you have it: evolution. It's a pretty good theory, but it seems a little lacking because it doesn't specify the barriers that would separate these systems, since they would only travel by passive diffusion. How would a new cycle "pinch off" from an old one?

At any rate, it's clear that something that can clearly be defined as life occured before RNA. This sounds like a pretty damn good idea, but it needs a little more data and a little more theory. I'm too lazy right now to look up the actual papers. Maybe if I'm feeling particularly bored I'll read some and post about them.

Och aye, the McCat is slain.

On Friday, I took that test of all tests, that exhalted exam, that furious final, the rite of passage for millions of let's-go-to-med-school-because-I-don't-want-to-do-research science students around the globe, the MCAT. To be honest, it really wasn't that bad, including the studying. I suppose I can say that now, looking back, after a solid weekend of pretty much nothing but Guitar Hero, fast food, and beer.

I know I "symbolized [my] signature by clicking 'Yes' to the non-disclosure agreement," but there was a random question about oximes (yes, oximes, of all chemicals), and I ----in' NAILED it. Synthesized by hydroxylamine hydrochloride? Yuh-huh.

Sorry. I had to get that out.

However, today I had a scary few hours when I realized that I never clicked "save" during the written portion. I just let time run out. Today, however, my saviour Meg let me know that it automatically saves my answer when I move to the next section. Looks like Andy's movin' up from a J to a K. Ohhh baby.

Anyway, I just read an awesome Scientific American article about the origins of life, and how the RNA world hypothesis probably isn't right. Too tired to post about it right now, but it'll come tomorrow.