The origin of the genetic cipher, the most perplexing problem in biology

(Otangelo Grasso) #1

The origin of the genetic cipher, the most perplexing problem in biology

The genetic code, with a few recently discovered minor variations, is common to all known forms of life. That the code is universal is extremely significant, for it suggests it was used by the common ancestor of all life, and is robust enough to have survived through billions of years of evolution. Without it, the production of proteins would be a hopelessly hit-or-miss affair. Questions abound. How did such a complicated and specific system as the genetic code arise in the first place? Why, out of the 10^84 possible codes based on triplets, has nature chosen the one in universal use? Could a different code work as well? If there is life on Mars, will it have the same genetic code as Earthlife? Can we imagine uncoded life, in which interdependent molecules deal directly with each other on the basis of their chemical affinities alone? Or is the origin of the genetic code itself (or at least a genetic code) the key to the origin of life? The British biologist John Maynard Smith has described the origin of the code as the most perplexing problem in evolutionary biology. With collaborator Eörs Szathmáry he writes: “The existing translational machinery is at the same time so complex, so universal, and so essential that it is hard to see how it could have come into existence, or how life could have existed without it.” To get some idea of why the code is such an enigma, consider whether there is anything special about the numbers involved. Why does life use twenty amino acids and four nucleotide bases? It would be far simpler to employ, say, sixteen amino acids and package the four bases into doublets rather than triplets. Easier still would be to have just two bases and use a binary code, like a computer. If a simpler system had evolved, it is hard to see how the more complicated triplet code would ever take over. The answer could be a case of “It was a good idea at the time.” A good idea of whom ? If the code evolved at a very early stage in the history of life, perhaps even during its prebiotic phase, the numbers four and twenty may have been the best way to go for chemical reasons relevant at that stage. Life simply got stuck with these numbers thereafter, their original purpose lost. Or perhaps the use of four and twenty is the optimum way to do it. There is an advantage in life’s employing many varieties of amino acid, because they can be strung together in more ways to offer a wider selection of proteins. But there is also a price: with increasing numbers of amino acids, the risk of translation errors grows. With too many amino acids around, there would be a greater likelihood that the wrong one would be hooked onto the protein chain. So maybe twenty is a good compromise. Do random chemical reactions have knowledge to arrive at a optimal conclusion, or a " good compromise" ?

An even tougher problem concerns the coding assignments—i.e., which triplets code for which amino acids. How did these designations come about? Because nucleic-acid bases and amino acids don’t recognize each other directly, but have to deal via chemical intermediaries, there is no obvious reason why particular triplets should go with particular amino acids. Other translations are conceivable. Coded instructions are a good idea, but the actual code seems to be pretty arbitrary. Perhaps it is simply a frozen accident, a random choice that just locked itself in, with no deeper significance.

That frozen accident means, that good old luck would have hit the jackpot trough trial and error amongst 1.5 × 1084 possible genetic codes . That is the number of atoms in the whole universe. That puts any real possibility of chance providing the feat out of question. Its , using Borel’s law, in the realm of impossibility. The maximum time available for it to originate was estimated at 6.3 x 10^15 seconds. Natural selection would have to evaluate roughly 10^55 codes per second to find the one that’s universal. Put simply, natural selection lacks the time necessary to find the universal genetic code.

(George Brooks) #2

Sometimes “survival of an arbitrary feature” is a matter of chance.

Lee is a very common name in China. Why? One could recreate the circumstances with a child’s game.

Take a small plastic pool (the kind used for children on a hot day). Put 1000 different names on 1000 cardboard fish and throw them in the pool. Every fish has a large paper clip attached to the head.

Then you and your children get sticks with string (like fishing poles) and tie or attach a magnet to the end of each string.

Then let the fishing being. Each person pulls two a fish out of the pool. It is a random process. Every 2nd fish is the WIFE of the first fish… and so her family name is eliminated. The name of the 2nd fish is crossed out, and the name of the first fish is written on the 2nd fish. Then BOTH fish are thrown back in the pool.

The process repeats and repeats and repeats.

At some point, you notice that every generation leads to half as many family names. And so, unless new/different names are constantly introduced into the pool… the number of family names INEVITABLY becomes quite small !

Why LEE? Or Wei? Or any other surviving family name?

Sometimes, it’s the randomness of survival that shapes generations forever.




Hello. Hope you like the forum. I notice that this is your second lengthy post. Are you going to defend your ideas or just post without interacting at all? Are these really your own ideas or did you copy them from some other site?

(system) #4

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