Is science sometimes in danger of getting tunnel vision? Recently published ebook author, Ian Miller, looks at other possible theories arising from data that we think we understand. Can looking problems in a different light give scientists a different perspective?

Where Did Life Begin?

Some time ago now I published an ebook "Planetary Formation and Biogenesis", which started with a review including over 600 references, following which I tried analyzing their conclusions and tried to put them together to make a coherent whole. This ended up with a series of conclusions and predictions on what we might find elsewhere. It was in light of this I saw the article in the May edition of "Chemistry World". That article put up reasons to back some of the various thoughts as to where life started, but I found it interesting that people formed their views based on their chemical experience, and they tended to carry out experiments to support that hypothesis. That, of course, is fair enough, but it still misses what I believe to bee the key point, and that is, what is the most critical problem to overcome to get life started, and how hard is it to do?

The hardest thing, in my opinion, is not to make polymers. I know that driving condensation reactions forwards in water is difficult, but as Deamer pointed out in the article, if you can get a lipid equivalent, it is by no means impossible. No, in my opinion, the hardest thing to do is to make phosphate esters. Exactly how do you make a phosphate ester? As Stanley Miller once remarked, you don't start with phosphoryl chloride in the ocean. The simplest way is to heat a phosphate and an alcohol to about 200 degrees C.  Of course, water will hydrolyse phosphate esters at 200 degrees C, so unless you drive off the water, which is difficult to do in an ocean, high temperature is not your friend because the concentration of water in the ocean always exceeds the concentration of phosphate or alcohol. You simply cannot do that around black smokers.

The next problem is, why did nature choose ribose? Ribose is not the only sugar that permits the formation of a duplex when suitably phosphated and bound to a nucleotide. Almost all other pentoses do it. So the question remains, why ribose? The phosphate ester is an important solubilizing agent for a number of biochemicals necessary for life but it invariably occurs bound to a ribose, which in turn is usually bound to adenine. The question then is, is this a clue? If so, why is it largely unnoticed? My conclusion was, ribose alone can form a phosphate ester on a primary alcohol group in solution because only ribose naturally has reasonable concentrations of itself in the furanose form.

It was not always unnoticed. There is a clearly plausible route, substantiated by experiment (Ponnamperuma, C., Sagan, C., Mariner, R., 1963. Synthesis of adenosine triphosphate under possible primitive earth conditions. Nature 199: 222-226.) that shows the way. What was shown here was that if you have a mixture of adenine, ribose and phosphate, and shine UV light that can be absorbed by the adenine, you make adenosine, and then phosphate esters, mainly at the 5 position of the furanose form, so you can end up with ATP, a chemical still used by life today. Why is that work neglected? Could it be that nobody these days goes back and reads the literature from 1963?
Why does this synthesis work? My explanation is this. You do not have to get to 200 degrees to form a phosphate ester. What you have to do is provide an impact between the alcohol group and phosphate equivalent to that expected at 200 degrees. If we think about the experiment described above, there is no way an excited electronic state of adenine can be delocalized into the ribose, so why is the light necessary?

My conclusion was that the excited state of the adenine can decay so that quite a considerable amount of vibrational energy is generated. That will help form the adenosine, but after that the vibrational energy will spread through the sugar. Now we see the advantage of the furanose: it is relatively floppy, and it will vibrate well, and even better, the vibrational waves will focus at C-5. That is how the phosphate ester is formed, and why ribose is critical. The pyranose forms are simply too rigid to focus the mechanical vibrations. Once you get adenosine phosphate, in the above experiment the process continued to make polyphosphates, but if  some adenosine was also close by, it would start to form the polymer chain. Now, if that is true, then life must have started on the surface, either of the sea or on land. My view is the sea is more probable, because on land it is difficult to see where further biochemicals can come from.
Posted by Ian Miller on May 28, 2017 11:45 PM Europe/London

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