The organic oceans concept for the origination of life on Earth, and by analogy, anywhere else it is, was that there were large quantities of organic compounds on the surface of Earth in the early days after its formation, and these served to facilitate the first self-replicating molecule. A phenomenon buttressing this is the formation of the moon, which is thought to have occurred after the impact of a large planetary body into the proto-Earth. This would create even more organic compounds, as would the ensuing volcanism.
The structure of a possible life origination theory has some essential components. One is the figuring out of a reasonably simple molecule which has the ability to replicate itself. Another is the figuring out of the conditions under which such replication can occur. Any theory which gets this far is a successful life origination theory, but there are a couple more things which are needed. One, call it the third component, is the portrayal of the physical mechanisms by which these conditions are provided. The fourth one is a superfluous one, and is the depiction of the continuation of life. A life origination theory which has those first three things is fabulous and a major step forward in science and many other areas, but if the life that is hypothesized necessarily dies out after some period, never evolving into human beings, then the theory is simply a demonstration that life can originate and how, not how the sequence of evolution that led to us got started. Having this fourth piece intact and robust makes the theory more complete and much more interesting.
The first three parts of life origination just have something reproducing itself, making copies one way or another. If some of the conditions in part two change, i.e., the physical mechanisms for producing them as part three of the theory stop working, the life that was originated ceases to maintain itself. As mind-wracking as part 1 is, part 4 may be just as hard, and just as hard many times over.
Molecules are like Lego blocks, as it is possible to assemble the various components in many ways. Coming up with a combination that replicates itself involves some critical components. Recall that one of the criteria for success was the ability to originate life in something less than the age of the universe or the age of the oceans. Two chunks of molecules that help in this timing problem are the hydrophilic and hydrophobic pieces, that bring a molecule to the meniscus between the organic pool and the water pool. This concentrates them, and reduces one of the big, likely the biggest, times in the process: the time to get the components next to one another.
Let's add a further requirement to the hydrophilic and hydrophobic pieces, in that they have positive intermolecular forces between themselves and a near identical molecule component. The hydrophilic piece would have an attraction to an identical hydrophilic one, and similarly for the hydrophobic one. This means that a slew of compound molecules, with one of each kind, would form a membrane at the meniscus. Solubility would line them all up and keep them at the boundary, and intermolecular forces would hold them together.
Consider what happens now. The two-piece molecule is lined up perpendicular to the mensicus. A hydrophobic piece, unattached to anything in particular, comes floating by and the intermolecular forces cause it to attach alongside the hydrophobic component of the two-piece molecule. Then the same thing happens with a hydrophilic component. If these two energetically are able to combine, we have … replication.
This meets part 1 of the requirements, except for being specific about which two molecules would do this. With all the hydrophilic and hydrophobic molecules that exist, let's hope there is at least one pair that would fill this role. Note that the replication is so elementary, it is necessary to think twice to see that the requirements are met. They are, but the conditions needed are strong. There has to be a reasonably high concentration of the special type of hydrophilic molecules floating in the water pool, and a reasonably high concentration of the other special type, a hydrophobic molecule, floating in the organic pool.
A variation of this simple-minded concept may be faster to execute. Suppose the replicator, the template molecule, is not a two piece molecule, but a three-piece molecule, with some connector between the hydrophobic and hydrophilic ends. It also has the requirement that it has strong intermolecular forces between itself and a copy of itself. Now, if we had one of the three component template molecules at the mensicus, and it encountered a copy of its middle section, it would hold onto it. If then it encountered a two component molecule, both ends would have intermolecular forces to the two ends of the three component template, and if the two component molecule could divide and reassemble around the extra copy of the middle component, we would again have … replication.
The generalization of this is obvious. If there is a template molecule with anything in between a hydrophilic and hydrophobic end, and it was located on the meniscus of the organic ocean and liquid ocean interface, and there were loose middle components around that would attach, and the separation of the hydrophilic end from the hydrophobic end was pretty easy to accomplish, as was the incorporation of the middle pieces, again there is replication. There might even be two or more stages of this.
Let's crib a little from biochemistry and ask if a fatty acid molecular component as the hydrophobic end would work. If the fatty acid was mostly or completely a linear backbone of carbon atoms, meaning a saturated one, the intermolecular forces might be proportional to the length of the overlap between the two backbones. With a middle component in one of the two touching molecules, there is less overlap, but if something were inserted, more. In other words, there might be a longitudinal force tending to separate such a fatty acid from a hydrophilic component connected to its carboxyl end. This would mean a two component molecule coming into contact with a three component group, the two ends being identical or close to it, would have a tendency to come apart between the components. This force should be small, as intermolecular London forces are small to begin with, so any separation would likely have to be aided in some other way. Finding the right middle component to facilitate this will be a challenge.
Part 2 of the requirements for a life origination there, determining the conditions under which it can happen, is almost pre-determined. There has to be, for the three-component template concept, free copies of the middle section, as well as two-component molecules in abundance, aligned with the meniscus. If we knew the details of the sundering of the two component molecule and the insertion of the middle component, we might estimate if there were temperature requirements, or even the presence of some other free component to catalyze the sundering, like chlorine atoms or sodium atoms. This will have to wait.
No comments:
Post a Comment