Review Of The Fifth Chapter Of Signature In The Cell By Stephen Meyer
Amidst the many memories that I cherish from my college undergraduate years are the get-togethers that friends and I would have to discuss the core textbook principles of molecular biology. Benjamin Lewin’s Genes IV stands out as one of the treasured resources we would pour over as we searched for the facts on the makeup of life. Perhaps most often visited amongst our topics of discussion were those of eukaryotic transcription and translation principally because for all of us there was something deeply unsettling about the naturalistic foundations upon which the emergence of these processes had been presented. So unsettled were we that we could never quite swallow the evolutionary suppositions that accompanied the factual details.
To recapitulate on what we now know about transcription, eukaryotes are furnished with three different RNA polymerases differing primarily in the types of genes that they transcribe. Each RNA Polymerase binds to a class of DNA sequence known as a promoter from which transcription then begins (1). A number of proteins called transcription factors, upon which these polymerases are absolutely dependent, form a functional transcription ‘apparatus’. RNA Polymerase II for example requires at least four transcription factors, TFIIA, TFIIB, TFIID and TFIIE for activity – a fact that is self-evident in Stephen Meyer’s pictorial outlines in the fifth chapter of his book Signature In The Cell.
The first step in the formation of the transcription apparatus involves the binding of TFIID to a DNA sequence upstream of the promoter’s own TATA box. TFIIA and TFIIB are then incorporated into the complex allowing RNA Polymerase II to bind to its recognition sequence in the DNA together with TFIIE (1). The functional interdependence of these molecules of course limits the amount of genetic change that can be tolerated by any one of the genes that codes for them. After all, any structural change in any one of the transcription factors would have to be accompanied by concerted changes in other factors within the complex as well as the RNA Polymerase II itself if functionality were to be maintained. This latter point, as relates to functional molecular complexes in general, was heavily emphasized in a seminal paper on Cambrian fauna by Meyer et al in 2001 (2).
In thinking of eukaryotic transcription I am reminded of Alexandre Dumas’ three musketeers who, like eukaryotic RNA polymerases, acted in unison in their endeavors. Ribosomal RNAs transcribed by RNA Polymerase I form part of the very ribosomes that then translate messenger RNAs, the latter having been transcribed by RNA Polymerase II. Similarly transfer RNAs (tRNAs), products of RNA Polymerase III, play their role in assuring the correct incorporation of amino acids during translation. Living up to the axiom ‘Un Pour Tous’, RNA Polymerases can be considered as the three chevaliers of the molecular realm.
As one reads Meyer’s summary of how the mechanistic details of transcription and translation were first unraveled, one cannot help but notice the amount of theoretical ground work that had been laid out before the first experimental results began rolling in. Contravening the ideas initially put forward by ‘Tie Club’ physicist George Gammow (see my review on the exploits of the Tie Club, Ref 3), Crick realized that the inherent structure of DNA could not in itself account for the amino acid sequence of proteins. In Meyer’s words “there is nothing about the chemical properties of the bases in DNA (or those in mRNA) that favors forming a chemical bond with any specific amino acid over another” (p.130). There had to exist a code embedded within but existing independently of DNA’s structural layout.
Francis Crick realized early on in his career that if DNA were to function as a code, it would require a series of adapter molecules that could in some way mirror the ‘letters’ or codons in the DNA sequence. Such molecules were later identified as transfer RNAs each of which we now know is coupled to a specific amino acid as a result of the activities of specialized enzymes called tRNA synthetases. Intermediate between DNA and proteins are messenger RNAs- transcripts of the code-rich sequence of DNA that migrate from the nucleus to the cytoplasm where ribosomes are ready in waiting to begin translation.
To this day seemingly unanswerable questions on the evolution of transcription and translation mechanisms continue to rattle the Darwin-faithful. As noted in an earlier review, gradually evolving the genetic code to provide the full complement of amino acid coding triplets would be lethal before it were beneficial simply because such alterations would impact the very proteins that make up the translation machinery (4). Along these same lines, biophycist Paul Davies famously remarked that “a change in the code risks feeding back into the very translation machinery that implements it, leading to a catastrophic feedback of errors that would wreck the whole process. To have accurate translation, the cell must first translate accurately”(5).
Meyer’s expository talent is visible in his extension of these same principles to other cellular processes such as DNA replication. Meyer fleshes out a cohesive argument in support of intelligent design garnering support from an extensive body of molecular evidence and expert commentaries. His review of the ‘chicken and egg’ paradox, as relates to the integral interdependencies of molecular systems such as transcription and translation, highlights once more why it is that evolutionary ‘pie in the sky’ assumptions are powerless to explain the origins of critical life processes.
Literature Cited
1. Benjamin Lewin(1990), Genes IV, Oxford Cell Press, 4th Edition pp. 543-546
2. Stephen C. Meyer, P. A. Nelson, and Paul Chien (2001), The Cambrian Explosion: Biology’s Big Bang, http://www.discovery.org/articleFiles/PDFs/Cambrian.pdf pp.34-35
3. Twenty Men In Matching Ties, And The Eternal Mystery Of The World’s Comprehensibility
http://www.arn.org/blogs/index.php/2/2008/09/07/twenty_men_in_matching_ties_and_the_eter
4. The Pioneers We Cherish: Reviewing The Achievements Of ‘Origins’ Biology, http://www.arn.org/blogs/index.php/2/2008/08/06/the_pioneers_we_cherish_reviewing_the_ac
5. Paul Davies (1999), The Fifth Miracle: The Search for the Origin and The Meaning of Life, Published by Simon and Schuster, New York, p.111