Protocells YAY!

I’m briefly surfacing from the stress ocean that is paper writing to do a little dance of joy about the latest mind-blowing development in origin-of-life research.

(With my ability to go on endlessly about random scientific subjects, you’d think I’d love writing papers. No, no, no, hell no. I wish I could just upload my methods and figures to some database and be done with it. >.<)

My latest great squeal about abiogenesis research was due to an RNA enzyme that could copy long RNA strands. Well, that’s still bloody amazing, but maybe massive RNA enzymes are not how the thing we call life started. Jack Szostak’s group works witn a model of early life in which enzymes aren’t needed at all.

They’ve been working for years and years on their protocells (illustration above by Janet Iwasa via exploringorigins.org). These are basically little fat bubbles floating around in a watery solution, with a bit of nucleic acid inside. The fatty membranes of protocells are made of much simpler materials than modern cell membranes. Protocells haven’t got any proteins, and contain just a tiny “genome” that doesn’t encode anything meaningful. Yet they can, under the right circumstances, grow and divide and pass on that genome to their descendants through ordinary physical forces.

And now, they can also copy it.

The problem so far was magnesium. RNA can be replicated by an enzyme, or it can, to an extent, copy itself using base pairing. Magnesium is necessary for both kinds of replication. However, the Szostak group’s fatty protocells quickly fall apart in the presence of magnesium, spilling all their RNA content.

Adamala and Szostak (2013) tested a bunch of small molecules that bind magnesium to see if they could help. Many of them could protect the protocells, but only one, citrate, could do this without also stopping RNA replication. As a bonus, citrate prevented the degradation of RNA that, under normal circumstances, eventually happens at high magnesium levels.

Like other research toward RNA replication, this study isn’t quite there yet. For one thing, the “genomes” of these protocells are very limited – they are tiny, and they are just runs of a single RNA building block, so it’s hard to imagine how they could be precursors to more “meaningful” genomes. Also, although a lot of organic molecules just spontaneously show up when someone tries to recreate early Earth chemistry, citrate is not one of them.

Nonetheless, little by little we’re edging closer to a living RNA world. We may never know how life actually started, but the research on how it could have started looks more exciting by the day…

***

Reference:

Adamala K & Szostak JW (2013) Nonenzymatic template-directed RNA synthesis inside model protocells. Science 342:1098-1100

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