Friday, April 20, 2012

How (some) antibiotics work

This research comes at a useful time: we're running out of usable antibiotics. They find that quinolones, beta-lactams and aminoglycosides (OK, I'm as wise as I was before, but those are classes of antibiotics) kill bacteria using hydroxyls to partly oxidize guanine. These defective guanines are taken up into bacterial DNA as though they were normal guanine (or as though it were thymine!)--but then they trigger the defect alarm, and the DNA-repair mechanism tries to split the DNA to splice it out. If there are too many of these, the DNA-repair kit winds up cutting the DNA in two places simultaneously, which it can't recover from.

That's cool. I don't quite understand why this mechanism effects bacteria and not normal body cells. Understanding that is the next step before you can develop some new antibiotics. Which I hope happens soon.


Texan99 said...

I tried and failed to look up the answer to this. I do know that the trick in killing bacteria without hurting host cells often involves differences in membranes, especially differences in how picky our ribosomes are about letting stuff in. Bacteria have very different systems for building walls around various processes, so you can get drugs to achieve strong concentrations in a bacterium's cytoplasm that you can't achieve in a eukaryotic cell's various compartments. Basically we guard our DNA more closely.

james said...

That would do it, if all our various cells use the same mechanism. Thanks!

Texan99 said...

The differences between eukaryotic cells (cells with a nucleus) and prokaryotic cells (no nucleus) are so vast that the differences between various types of human cell are trivial in comparison. Bacteria have no nuclei; all of our cells do. In fact, all cells of all multicellular organisms do, I think. The split between us and bacteria is very, very old.

So although there are lots of differences among our cells, none of them is anything like as profound as the difference between us and bacteria concerning where we put our DNA and how we protect it. The DNA of a bacterium floats around loose on the street. Ours is in Catholic boarding school behind a moat.