Wednesday, September 15, 2004

glycosylation

Monosaccharides react easily with alcohols (R-OH) and amines (R-NH2). This happens on the anomeric hydroxyl (-OH), the hydroxyl that is attached to the anomeric carbon (duh!). Other hydroxyl groups do not react. This is called glycosylation (of the alcohol or amine), where the -OR and -NHR are incorporated into the monosaccharide. The products are called called O-Glycoside and N-Glycoside, respectively. Water is released, a condensation reaction. Because water is lost, the monosaccharide units of oligo- and polysaccharides are thusly called residues.

Glycosides of monosaccharies have no reducing properties because of the loss of the aldehyde group on the anomeric carbon, and their ring structure cannot open to give straight-chain structures, hence, they don't exhibit mutarotation. Glycosides of polysaccharides, however, can be reducing (e.g., maltose) or not (e.g. sucrose). It really all depends on whether the anomeric hydroxyl group has reacted or not.

And while we're at it:
amino group: NH2
acetyl group: COCH3

I took the TOEFL test last saturday.

I almost arrived late for it. I had Sears repair appointment in the morning for my elliptical. I waited till 12 noon but the damn repair guy didn't show. I decided to take a taxi to the test site, which was somewhere in South Boston near the pier. All went relatively smoothly until about half of the way through the test when my computer froze. Fortunately, all my answers were saved and I was able to resume right where I left off. I said "relatively smoothly" because, all the while I was taking the test, there was some banging going on probably due to some construction in the next door office. Furthermore, there was a guy behind me constantly cursing, banging his desk, and throwing stuff about his station. I'm guessing he was not having a very good day.

Anyway, I practically aced the listening, reading, and sentence structure portion of the test. However, I had a bit of a problem with the essay. I mean, given enough time, I would have probably created a score 6 essay. Since I am only given 30 minutes to do it, my essay came off simplistic yet again. I was not able to expound on my points. I've decided that I hate doing essays. Typing up this blog takes me at least 40 minutes - and I'm not kidding. Words just don't flow easily from me, be it in essays or in conversation.

now playing: Stravinsky - Les Noces (Bernstein, Deutsche Grammophon)

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