One in a million!

Posted: May 16, 2006 in Intelligent Design

images[3].jpgI’ve been reading the book  ‘Life’s Solution’ by Simon Conway Morris.In it he discusses the efficiency of the genetic code in relation to minimising the damage an error during transcription and translation would have on an individual organism.(Transcription is the process whereby the genetic information stored in DNA is copied across to RNA. Once the information is in the form of RNA the process of translation occurs, this involves decoding of the RNA to produce a polypeptide chain of amino acids-The primary structure of Protein).

Nucleotide bases read by the translation process code each of the 20 left handed amino acids used in nature. The nucleotide bases are read in groups of 3 known as triplets. There are 4 possible bases from which to make up the triplets, reading them as a combination of 3 bases gives a possible combination of 64 available triplets. There is a high degree of redundancy (the same end is arrived at via different means), Such that some amino acids are coded for by as many as 6 different codon’s. This redundancy minimises the amount of damage having the wrong amino acid in a protein might mean.

The amazing, yet generally unappreciated feature of the genetic code that both we, the wood that makes up your table, the bacterium in your gut and the humble nematode munching on the compost heap share, is that when a single (point) mutation happens the difference between the intended (correct) amino acid and the actual amino acid coded for due to error, is usually relatively harmless. The key characteristic of the amino acids with redundancy is hydrophobicity (amino acids repelled by water). This is because the 3-D shape of the final protein is partly dependant on the forces of water attraction and repulsion.3-D shape is important in the same way that the shape of a key and the lock it opens are vital for a functioning lock Protiens interact and form structures based on there shape.

Stephen J. Freeland and Laurence D. Hurst used computer simulations to look at exactly how efficient the genetic code is in relation to what might have been?

Freeland and Lawrence had to place within there computer program all the nuances seen in nature such as the observed increase in relative frequency of mutations due to mistakes seen at the third position of the triplet mRNA during translation. Mistakes occur frequently at this position due to a weak-binding affinity between mRNA and tRNA   dubbed a ‘wobble’ by DNA’s co discoverer Francis Crick.

Codon’s which code for the same amino acid due to redundancy of the should usually differ by there last letters (third base) so the common mistakes generated by weak binding at the third base in a codon generate a (wobble). So mistakes at the third position in a codon often give the same amino acid as was initially intended.Freeland and Lawrence randomised the genetic code leading to a massive number of alternate possible codes, one in a hundred million  then compared the efficiency in terms of redundancy .They produced the bell curve with almost all there computer generate codes being in the bell –when comparing the efficiency of the bell curve codes with  the code we have within us they found our natural code was far far more efficient .

Freeland and Lawrence tell it like this ‘…the natural genetic code shows evidence of optimisation, two orders of magnitude higher than has been suggested previously…..under our model, of 1 million random variant codes produced ,only 1 better …than the natural code –our genetic code is quite literally 1 in a million !’

I guess I find it hard to reconcile this statement with the preverbal  visually impaired watchmaker.

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