I'm sure I should feel happier...

Well...I handed my dissertation in. I'm sort of waiting for a nice happy heartfelt rush of relief, or some kind of feeling. Something other than cold and tired would be nice.

It did look all professional though; bound up properly with some nice results, pretty pictures and surprisingly meaningful graphs. And I think I'll probably feel better tomorrow, when I hand my lab book back to my supervisor in the safe knowledge that she's continuing with the work we were doing, and may yet find something even more interesting. At the moment though I'm kind of oscillating between oh-my-ghod-so-much-revision and well-there-goes-10%.

So if you want some interesting science go here for snails that ride on other snails, and other easy-to-understand scientific awesomeness from Ed Yong.

And if you want some mind-knotting philosophy go here for a discussion of induction that I feel so proud to actually understand (eventually and after much discussion)

(and if you want general fun, go to xkcd because it's always good)

How bacteria make antibiotics

There are many different types of antibiotics bacteria can make, but my lab project (now finished, alas) was concentrating mostly on a type called polyketides. These are not just antibiotics, some polyketides can also be antifungals and anticancer agents too, so it's not surprising that quite a lot of work has been done characterising their formation.

Here is the molecular structure of erythromycin. Like many polyketides it is circular, which at first appears to be a bit of a headache to synthesise. The way it's put together, though, is actually very clever. The backbone of the circular section is made up first, using a system of modular enzymes that pass the growing chain along like a conveyor belt, adding new residues at each stage. Then the straight chain is curled up into a ring, and finally the two side residues (the ones on the bottom right of the chemical structure, that look a bit like squashed rectangles with dents in them) are stuck on.

So here is the picture that has appeared on every slide show in every lab meeting we've had this term, showing the formation of the straight-chain backbone before it gets curved into a circle:
Ignoring the little letters (which are just names of enzymes) it really does look a lot like a conveyor belt. At each stage the chain is lengthened, before finally being taken off and twisted around onto itself (to form a circular molecule called DEB). The modular nature of this system is fascinating to work with, but a real problem to sequence. DNA sequencing techniques work mainly by chopping the genome up, sequencing the bits, then trying to stick them back together and modular repeats tend to confuse them.

The last stage, going from DEB to erythromycin, is just a matter of decoration. Although the squashed-rectangle additions (glycosylases, added by glycosylation I believe) look complex, they are quite common molecules that get added onto things in the cell. Glycosylase residues and glycosylation enzymes are very common.
And that's how bacteria make polyketides :)