Uncommon Descent Serving The Intelligent Design Community

The Finely Tuned Genetic Code

Jonathan M
November 19, 2011
Intelligent Design
1
Categories
Intelligent Design
Share
Facebook
Twitter/X
LinkedIn
Flipboard
Print
Email

Francis Crick regarded the genetic code found in nature as a “frozen accident.” Yet more and more it is looking to be the case that this code is exquisitely finely tuned — with features suggesting it is indeed one in a million. Therefore ought not purposive or intelligent design be regarded as a legitimate inference, as the best explanation for how the code came into existence?

Click here to continue reading>>>

Comments
OT: New Video of William Dembski:
How Do We Detect Design in Nature? One Minute Apologist With William Dembski - video http://www.youtube.com/user/oneminuteapologist#p/u/1/0TFsnQo5LE4
bornagain77
November 20, 2011
November
11
Nov
20
20
2011
10:55 AM
10
10
55
AM
PDT
ChasD you state:
After all, the code is only “one in a million”. If there are 10^70 codes, that means there are 10^64 better codes than ours –
And, besides your blanket assertion that there are 10^64 better codes than the DNA code, what is your actual evidence to prove there is ANY conceivable DNA code better than the optimal one we find in life??bornagain77
November 20, 2011
November
11
Nov
20
20
2011
03:12 AM
3
03
12
AM
PDT
I disagree with the "selection" hypothesis myself. This does not, however, mean that design is the only alternative. After all, the code is only "one in a million". If there are 10^70 codes, that means there are 10^64 better codes than ours - why don't we have one of them? The degeneracy and chemical conservatism of the modern code is plausibly derivable from constraint upon expansion of a narrower code set, not from competition between random variants on the 20-acid code. This piece makes the common assumption that 20 amino acids is the minimum requirement for functional protein-based catalysis, and that codon assignments are considered to be just pulled out of a bag entirely at random. While everything alive today uses that 20-acid system, this only means that nothing using a smaller set has left descendants through to the present that continue to do so. To illustrate by a reductio ad absurdum, imagine that there was just one amino acid. All you could make is poly-alanine, and you do it by passing RNA through a ribosome. Because you are polymerising amino acids, which have a certain distance between links, you are constrained in the width of code units. You are also constrained by the strength of bonding between the tRNA and mRNA, and by inevitable curvature of the tRNA anticodon. A one-base code would be too wobbly and short; a four-base code too tightly bound and difficult to keep linear in the tRNA. So the code is triplet, but not for coding reasons. Now, if you start with such a system, where every codon means either "alanine" or STOP, it is obviously even more degenerate than the current system - 50- or 60-fold degenerate, depending how many bases are covered. If another amino acid is added to the system, that substitution is least disruptive if it is chemically related. This constraint means that subsequent errors that mistranslate one acid for another seem to be chemically conservative as if by magic - but really, they simply reflect the historic constraint on code expansion. Now you have divided your code set in two - and the obvious way to do that is to tighten up the specificity at one codon position. You don't need precise specificity, as the requirement only demands a two-way choice - so base-blindness at that position becomes purine-pyrimidine specificity, not absolute base distinction in all 3 positions. That gives you transition-transversion bias protection, again as if by magic - the mechanism of tightening specificity is the stereochemical distinctness of the two classes, which happens to be the reason why there is a transition-transversion bias. By a succession of such progressive additions, all subject to the same constraints on chemical conservatism and retention of codon blindness (-> 16-fold or 4-fold degeneracy depending on the number of bases involved) or purine-pyrimidine specificity only (-> 8-fold or 2-fold degeneracy) it is possible for an apparently optimised code to arise. Degeneracy actually goes down, but the reward is greater catalytic flexibility, and sufficent residual degeneracy remains to surprise the investigator. I am aware that this is hypothetical. I am also aware that poly-alanine has no obvious functional value.Chas D
November 20, 2011
November
11
Nov
20
20
2011
02:53 AM
2
02
53
AM
PDT
1 2

Leave a Reply