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DNA is a structure based on chemistry. But simple? In a single cell there are 147 billion base pairs. In a single human body there is enough DNA to stretch from here to the edge of the solar system. In other words, we carry far more information than any human being could possibly comprehend.
Yes it is simple chemistry and simple amounts of a substance do not imply incomprehensible complexity. Second of all while a single human may not comprehend the information, the scientific enterprise called the Human Genome Project has decoded the entire genome and while the understanding of the function of every DNA segment is not known a huge amount is...over time the rest will be figured out but it is more a quesition of brute force figuring out the gene regulation than a theoretical problem.
Your comments on chirality miss the point. First niether of the references I posted are from textbooks...they are primary research literature papers describing actual experiments. Second if a biological system uses L amino acids which chemically excludes D form, then all subsequent proteins will be L since they cannot incorporate D...once the choice is made randomly you cannot pick and choose each time de novo. And in any case, one of the papers I cited shows there are mixed chiral proteins and they function.
..edited out my goof...apologise to defender and thanks to WK for pointing out my error.
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DNA experiences copying errors, yet it still functions. It passes on errors, but it still manufactures proteins, regulates cell behaviour, etc. As long as the error is not fatal, the organism may survive.
But mutation is an error in reproduction. If DNA had a 'circuitry' error in the first place, on account of having a single left-handed nucleotide, it simply wouldn't work. The cell could not reproduce and there would be no reproduction at all.
Not sure what you are getting at here...if a wrong handed base were placed in a DNA molecule it would be removed by excision repair or one of the other repair enzymes...most polymerases (in the lab) when faced with a problem insert bases at random (Ok not entirely at random..Taq favors Adenosine)....and as long as this does not disrupt a the protein sequence you could express the protein and not notice the difference.
And besides if you are referring to abiogenesis and the first molecules of life, it is currently thought to have been RNA as RNA can catalzye multiple reactions without proteins..DNA cannot...so DNA would have been irrelevant to the origin of self replicating molecules..though not to the evolution of them.
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I would also like to find a documented example of evolution (an addition of genetic information through mutation) that has occurred in any laboratory.
There are lots but here are a few..some of the others may wish to post those from their respective disciplines
Proc Natl Acad Sci U S A. 2003 Feb 4;100(3):1072-7. Epub 2003 Jan 21. Related Articles, Links
Parallel changes in gene expression after 20,000 generations of evolution in Escherichiacoli.
Cooper TF, Rozen DE, Lenski RE.
Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824, USA. cooperti@msu.edu
Twelve populations of Escherichia coli, derived from a common ancestor, evolved in a glucose-limited medium for 20,000 generations. Here we use DNA expression arrays to examine whether gene-expression profiles in two populations evolved in parallel, which would indicate adaptation, and to gain insight into the mechanisms underlying their adaptation. We compared the expression profile of the ancestor to that of clones sampled from both populations after 20,000 generations. The expression of 59 genes had changed significantly in both populations. Remarkably, all 59 were changed in the same direction relative to the ancestor. Many of these genes were members of the cAMP-cAMP receptor protein (CRP) and guanosine tetraphosphate (ppGpp) regulons. Sequencing of several genes controlling the effectors of these regulons found a nonsynonymous mutation in spoT in one population. Moving this mutation into the ancestral background showed that it increased fitness and produced many of the expression changes manifest after 20,000 generations. The same mutation had no effect on fitness when introduced into the other evolved population, indicating that a mutation of similar effect was present already. Our study demonstrates the utility of expression arrays for addressing evolutionary issues including the quantitative measurement of parallel evolution in independent lineages and the identification of beneficial mutations.
Proc Natl Acad Sci U S A. 2001 Sep 25;98(20):11388-93. Related Articles, Links
Contribution of individual random mutations to genotype-by-environment interactions in Escherichia coli.
Remold SK, Lenski RE.
Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824, USA. remold@msu.edu
Numerous studies have shown genotype-by-environment (GxE) interactions for traits related to organismal fitness. However, the genetic architecture of the interaction is usually unknown because these studies used genotypes that differ from one another by many unknown mutations. These mutations were also present as standing variation in populations and hence had been subject to prior selection. Based on such studies, it is therefore impossible to say what fraction of new, random mutations contributes to GxE interactions. In this study, we measured the fitness in four environments of 26 genotypes of Escherichia coli, each containing a single random insertion mutation. Fitness was measured relative to their common progenitor, which had evolved on glucose at 37 degrees C for the preceding 10,000 generations. The four assay environments differed in limiting resource and temperature (glucose, 28 degrees C; maltose, 28 degrees C; glucose, 37 degrees C; and maltose, 37 degrees C). A highly significant interaction between mutation and resource was found. In contrast, there was no interaction involving temperature. The resource interaction reflected much higher among mutation variation for fitness in maltose than in glucose. At least 11 mutations (42%) contributed to this GxE interaction through their differential fitness effects across resources. Beneficial mutations are generally thought to be rare but, surprisingly, at least three mutations (12%) significantly improved fitness in maltose, a resource novel to the progenitor. More generally, our findings demonstrate that GxE interactions can be quite common, even for genotypes that differ by only one mutation and in environments differing by only a single factor.
There are many many more from this group and others...
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Scientists have not yet been able to purify the natural mixture of nucleotides to one specific chirality. They know that specific chirality is essential for the proper function of DNA, which is essential to life. It has not been explained how random chance could have put together a DNA molecule with nucleotides of only the right-handed chirality, having countless nucleotides to put in and an equal selection of right- or left-handed ones in the environment.
Your mention of alcohol is precisely my point. Scientists cannot purify alcohol, much less reduce a random collection of amino acids to one particular chirality... which is what working proteins need... not even with modern intelligence and technology. So how was it achieved by random chance?
This is a mere argument from your own personal incredulity...that 100% pure compounds are not obtained in the lab is a limit of modern science not a constraint on nature...and as I have pointed out..nature is leaky..any protein that incorporates the wrong amino acid or DNA strand that incorporates the wrong base (happens a lot actually) will not be visibile as it gets selected out of the proteome, genome, or the individual is not viable...and it is NOT an unlimited pool that you can select from..once you have chosen D or L you have to stick with one and not flip flop..thus it is chemically constrained by the first choice made.
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I'm not referring to the production of other molecules after the first molecule, but rather how the first molecule could have formed in the first place with a specific chirality.
Random chance.
[This message has been edited by Mammuthus, 08-25-2003]
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