Most molecules don't do anything. They usually sit, surrounded by others of their kind, in a bottle on the shelf in a chemical laboratory, just waiting for somebody to do something to them. The concept of them doing something to themselves, or to other molecules, is a bit far-reaching. Yet, the concept of chemical evolution demands it. How is this to be reconciled with what we know about ordinary chemicals?
What is the most we might expect of a molecule? Perhaps it could break a bond on another chemical by interacting with it, or perhaps join up with something else. The idea of a complicated molecule, say with ten atoms or more, much less a hundred or two, making another of the same kind is so extreme as to be unthinkable. Is that what we need a Replicator to do?
What happens in a real biological cell? Phenomenal things. DNA wraps itself up or unwraps itself at the appropriate time. Various enzymes produce proteins. The message coded into the DNA is turned into some unique proteins that accomplish some amazing things. The cell wall has a very sensitive permeability to things it wants to let in. There is a whole slew of energy producing molecules produced by microscopic energy factories. And on and on. The biological world is so complicated, so sophisticated, so engaging, that it leaves any chemical arrangement looking like nothing worth mentioning.
But perhaps there is something to be learned by analogy. An enzyme typically does not produce its target organic protein output out of elemental atoms. It is not juggling three hundred atoms and trying to make them all go to the right places. It is doing a simple cut or join of some other proteins or other molecules. Why couldn't we have chemical evolution doing something simple like that as well?
Suppose we have a strong of amino acids hooked onto the organic side of the meniscus membrane. Could they, perhaps aided by some ions floating around in the vicinity of the membrane, hook together a string of other amino acids which were just in the neighborhood? Could a ten amino acid combination somehow facilitate the production of a ten amino acid combination? Things don't have to be perfect. If the ten amino acid combination makes a hundred amino acid combinations before it is sundered into its parts, and ninety eight of them are random things and two are copies of itself or its mirror image in some system of pairing, then it is a replicator. In a cell, it would be insanely inefficient for an enzyme to make ten mistakes while producing one copy of the right protein, but chemical evolution is not taking place in a cell, it is taking place in an organic ocean, where detrius, meaning mistakes, can be flushed away, while the two correct copies adhere to the membrane and begin their own copying adventures. Efficiency can come much later.
In a cell, as far as we know, there is one energy currency, ATP. If an enzyme is busy making some join that is energetically not possible, ATP can come along and supply the energy needed to do it. Is there a possible energy source in the meniscus membrane situation? Could it be some ion is transported along the ambiphilic molecules from the water side to the organic side, but never into solution there, just to the amino acids or some other molecules hanging onto the lipophilic end? When the energy transfer is done, the ion is allowed to drift away connected to some small organic molecule. Where would this wonderful energy originate? In a cell, it could come from photosynthesis or from some complex carbohydrate that was available. In the oceans, perhaps it comes from photodissociation or from thermal effects or volcanic effluent or something else that can be stored in molecular form for a while.
If we make the assumption that almost everything in chemical evolution is done with amino acids, are there enough in the organic ocean to make it possible? Recall the enormous times available. If a typical replicator takes a year to make two copies, in a few decades the first such molecule will have taken over the oceans. Only one is needed to start, and if that takes ten million years for the first one, it is enough, as the period of life origination is many times that.
Could the meniscus membrane be fashioned from amino acids? If so, then fabrication of it at some later stage of chemical evolution might be easier. Are there any amino acids which are hydrophilic, perhaps with the addition of a metal ion or something else? Probably many are lipophilic. If none are or can be made hydrophilic, at least the organic ocean side of the molecule can be made of amino acids.
The organic ocean side is likely almost entirely made of molecules which do not interact with the meniscus membrane at all. Hundreds of organic molecules, anything with five or six or more carbon atoms, is likely to be a part of it. All these do not alter the molecule, do not adhere to it, and by and large do not do anything to whatever does attach to it. They serve to provide the liquid that makes the meniscus, and dissolve the interesting molecules.
If there is some depth to the organic ocean, it is possible to ask if there is any depth variation of composition. Do a thought experiment. If you have two miscible liquids, one of which is more dense than the other, and you mix them and put them in a very tall tank, is what is on the bottom the same as what is on the top? Does the relative density make any difference at all? It makes sense that the more dense one will be more concentrated at the bottom of the tank. There has to be a balance of the forces of gravitation and random kinetic motion of liquid molecules. For gases, this is pretty easy to figure out, but for liquids, harder. Anyway, it makes sense that more dense liquids would concentrate to a degree at the bottom of the organic ocean. Assuming that the combined organics are still lighter than salty water, they would be on top. The density surmise indicates that the light stuff, the five carbon stuff and close relatives, would be at the top, and down by the meniscus, heavier molecules. Like amino acids, for example. If they were produced by lightning at the top, they would drift down. Sometimes, things just seem to fit together.
No comments:
Post a Comment