How big protein complexes assemble, and why Ferritin is awesome

What sort of sadist makes poor 3rd year students take an exam at 9am on a Saturday? The Molecular Biology department at my university, that’s who.

The exam was “assembly of supramolecular structures” – how big massive complicated protein complexes assemble.
I was pretty nervous about this one, during revision I just felt that no specific details were sticking to my brain. There were only a couple of topics from the module I felt confident about.

I wanted to write about ferritin. Ferritin is basically a hollow protein shell that sucks up iron into its innards. It has incredibly high affinity for iron – if you put it in an iron test tube, it would actually slurp the metal out of the tube. If you don’t find that utterly thrilling then there is evidently something wrong with your brain’s thrill receptors.

I even made a model of it, look, it’s cute:

I didn’t get asked about ferritin. Instead I wrote about the tobacco mosaic virus (TMV), and the formation of amyloid proteins. I was very lucky with the questions I was given to choose from, thank llama.

The TMV essay asked me to explain the experimental evidence that indicated how the long rod-shaped virus assembles. I was able to explain how they found out that the rod is built up from disk shapes stacking on top of each other, but when it came to explaining how the genetic material gets inside the protein coat I was stumped. I know how it happens, I just couldn’t remember the experiments that were done to prove it. EEK. So what I did was made up experiments that I would do it show how it’s done. I hope they’ll let me get away with that.

This is TMV:

Amyloids occur when protein folds up all wrong. Sort of. It’s actually more like “oh no this protein has folded itself in to a knot – so to stop it going renegade and causing havoc, I’ll fold it in to a nice stable amyloid form that’ll just hang around not doing much”. Unfortunately, over time amyloid can build up and melt yer brain.
Diseases like CJD are caused by prions, which is a sort of amyloid protein. I’ve always been pretty interested in this topic so I had plenty to ramble on about.

Three more exams to go now. I hope my hand doesn’t fall off from all the writing. Holding a pen is already painful because I slammed my finger in a door the other day, oops-a-daisy.

Disclaimer: I’m only taking my lecturer’s word for it that ferritin slurps iron out of a text tube.