Saturday, December 14, 2013

New Szostak protocell is closest approximation to origin of life and Darwinian evolution so far - The Panda's Thumb

Link: http://pandasthumb.org/archives/2013/12/new-szostak-pro.html

This is the first time that nonenzymatic RNA copying succeeded inside a fatty acid vesicle. The big obstacle has always been that magnesium ion Mg2+ was necessary for RNA copying, but two negative side-effects of high Mg2+ levels frustrated success. Firstly, high Mg2+ levels break down the simple, fatty acid membranes that probably surrounded the first living cells. Secondly, Mg2+ catalyses degradation of single-stranded RNA. After a long trial-and-error process, Szostak et al. discovered that citrate removes these two side-effects. Citrate efficiently protects fatty acid membranes from the disruptive effects of high Mg2+ ion concentrations, while both allowing RNA copying and protecting single-stranded RNA from Mg2+-catalyzed degradation.
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A working version of a complete protocell has not yet been achieved in a laboratory setting. Other problems need to be solved, such as the fact that citrate is not a plausible prebiotic component: it needs to be replaced by an alternative component. Finally, at a certain level of complexity, a third main component of the cell would be helpful: chemical energy (metabolism). Nevertheless, conceptually and practically, the Szostak protocell is the closest approximation so far to the origin of life forms which have the potential to evolve.


From the comments:
Do follow the link under the picture (above). There are some really cool animations there.
For those of use who don't stare through a microscope each day, it's hard to remember that these are not "static" structures, like our skin or bones or organs, or like static pictures on a page. These are instead fairly loosely (or at least dynamically) held individual molecules, that are always in random thermally generated Brownian motion. Once you see the parts of the assemblage all wiggling about, it becomes much more plausible to imagine them interacting in some fashion.
When all we see are static pictures or drawings, explaining how this large molecule fits like a key into this other large molecule, it becomes reasonable to ask, "Well, how did the cell know to grab molecule "A" and stick it to molecule "B"?". With only the static drawings, it looks like a well defined key in an unchanging lock. Even simple animations often just show the static "key" molecule approaching the static "lock" molecule, in a well controlled manner, turning the lock, and then moving on. Even animations of the assembly or copying of DNA or RNA typically show precise, "intentional" motions of the molecules in question.
But, looking at animations like these, it becomes more clear that we're talking about relatively flexible structures all wiggling about, all bumping into each other, in relatively rapid and random ways, and that, occasionally, two of those flexible structures will stick together in certain ways. Given the nature of those structures, two molecules are more likely to stick together in one way than in another.
Looked at another way, we (the lay public) tend to imagine these molecular parts acting as we see desecrate objects acting around us in our daily lives. We don't have the personal experience of parts (molecules) where the environment (water) is on the same scale as we are, and where the interactive forces between molecules bumping into each other is on the same order of energy as the forces holding the parts together.
It's like the difference between walking from one exhibit to another in a relatively sparsely populated museum, and trying to move from one side of a densely populated train platform to another, where you are literally check to jowl with all the other people all constantly bumping into each other.
Detailed, dynamic animations like these are wonderful teaching tools to better show what is really going on.

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