IN 1953, STANLEY Miller, a graduate student at the Uy of Chicago, took twoflasks—one taining a little water to represent a primeval o, the other holding amixture of methane, ammonia, and hydrogen sulphide gases to represeh』s earlyatmosphere—ected them with rubber tubes, and introduced some electrical sparks as astand-in fhtning. After a few days, the water in the flasks had turned green and yellow iy broth of amino acids, fatty acids, sugars, and anipounds. 「If Goddidn』t do it this way,」 observed Miller』s delighted supervisor, the Nobel laureate HaroldUrey, 「He missed a good bet.」
Press reports of the time made it sound as if about all that was needed now was forsomebody to give the whole a good shake and life would crawl out. As time has shown, itwasn』t nearly so simple. Despite half a tury of further study, we are no osynthesizing life today than we were in 1953 and much further away from thinking we .
Stists are now pretty certain that the early atmosphere was nothing like as primed fordevelopment as Miller and Urey』s gaseous stew, but rather was a much less reactive blend ofnitrogen and carbon dioxide. Repeating Miller』s experiments with these more challenginginputs has so far produced only one fairly primitive amino acid. At all events, creating aminoacids is not really the problem. The problem is proteins.
Proteins are what you get when you string amino acids together, and we need a lot of them.
No one really knows, but there may be as many as a million types of protein in the humanbody, and eae is a little miracle. By all the laws of probability proteins should.
To make a protein you o assemble amino acids (which I am obliged by long tradition torefer to here as 「the building blocks of life」) in a particular order, in much the same way thatyou assemble letters in a particular order to spell a word. The problem is that words in theamino acid alphabet are often exceedingly long. To spell collagen, the name of a ontype of protein, you e eight letters in the right order. But to make collagen, youe 1,055 amino acids in precisely the right sequence. But—and here』s anobvious but crucial point—you don』t make it. It makes itself, spontaneously, withoutdire, and this is where the unlikelihoods e in.
The ces of a 1,055-sequence molecule like collagen spontaneously self-assembling are,frankly, nil. It just isn』t going to happen. To grasp what a long shot its existence is, visualize astandard Las Vegas slot mae but broadened greatly—to about y feet, to be precise—to aodate 1,055 spinning wheels instead of the usual three or four, and with twentysymbols on each wheel (one for eaon amino acid).
1How long would you have topull the handle before all 1,055 symbols came up in the right order? Effectively forever. Evenif you reduced the number of spinning wheels to two hundred, which is actually a moretypiumber of amino acids for a protein, the odds against all two hundred ing up in a1There are actually twenty-two naturally amino acids known oh, and more may await discovery,but only twenty of them are necessary to produce us and most other living things. The twenty-sed, calledpyrrolysine, was discovered in 2002 by researchers at Ohio State Uy and is found only in a siype ofarchaean (a basi of life that we will discuss a little further on iory) called Methanosara barkeri.
prescribed sequence are 1 in 10260(that is a 1 followed by 260 zeroes). That in itself is a largerhan all the atoms in the unive