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Crick's central dogma: Information flows in molecular biology and scientific discourse

ResearchBlogging.org
Following the discovery of DNA structure by Watson and Crick (as well as Franklin, the crystallographer—I'm very partial to crystallographers!) in 1953, Crick went on to construct the central dogma, stating it in 1958 and restating it in 1970.
Why the restatement? Because during the period in-between, other people have come up with responses to it; evidently, Crick is dissatisfied with those articles that 'misunderstood' (Crick's own wording) the idea of central dogma.
To be fair, when I hear the term 'central dogma' in a Biology class, I was perplexed, too. The term 'dogma' belongs to philosophy, specifically epistemology, what is it doing here in a Biology class? If the Wikipedia page is to be believed, basically, Crick couldn't find a more awesome word. Hypothesis was taken by sequence hypothesis; framework probably sounds too ordinary; axiom probably sounds too mathematics-y; truth probably sounds too epistemological. Though considering that the central dogma describes universally almost every genetic system, it may be just a little exaggeration to call it universal genetic truth or something like that.  
Your Biology teacher probably explains the central dogma like this: In genetics, there are three important macromolecular carriers of information — DNA, RNA and proteins. DNA is inherited from your parents and sit in your cell nucleus (and mitochondria); DNA is replicated in cell division; DNA is transcribed to RNA. RNA (specifically, mRNA) is translated to proteins by the ribosomes. Central dogma is thus that framework in which the genetic information encoded in the DNA is finally expressed as proteins; it's a schematic of (genetic) information flow. Understand, class? And at this point, Crick would shake his head, raise his hand, and say, "If I may elaborate?"
And that is exactly what Crick wrote in the 1970 Nature paper. He would like to "explain why the term was originally introduced, its true meaning, and state why [he] think[s] that, properly understood, it is still an idea of fundamental importance."
The abstract:
The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred from protein to either protein or nucleic acid.
Crick would like to point out that the central dogma is a negative statement, while the earlier sequence hypothesis is a positive statement. Thus it is intentionally limiting: the genetic information ends in protein and stays there—it's a cul-de-sac.
There are 3 other misunderstandings that Crick addressed, but I will leave it to you to read for yourself.
This whole chronicle of central dogma—besides teaching us about information flow in molecular genetics—also says something about information flow in scientific discourse.
First, the way Crick formulated the central dogma is exemplary. Early molecular geneticists knew about DNA, RNA, and proteins; but how the genetic information flows among them was less elucidated. Crick and and his collaborators first assume that all possible information transfers exist (Figure 1, as reproduced below). 
From there, they took away the arrows. They realised that two-way arrows are improbable because forward transfers already involve complex machinery, so "it seemed unlikely that that this machinery could easily work backwards". Protein-to-protein was out, too, because of  "stereochemical reasons"; in other words, proteins that so depend on their 3D structure to function cannot simply transfer its sequential information, like the nucleic acids which possess base-pairing that make replication possible for the nucleic acid since it serves as its own template.
And if this whole process sounds like detective work, well, that's the other way round; reasoning is the basis for both science and detective work, in this case deduction in particular. I particularly like the way they dismantle the arrows that did not stand up to scrutiny, it's kind of Holmesian.
Second, the precise way Crick formulates the central dogma. Crick formulated that abstract with extraordinary precision that stood up to scrutiny. He said:
In looking back, I am struck not only by the brashness which alowed us to venture powerful statements of a very general nature, but also by the rather delicate discrimination used in selecting what statements to make. Time has shown that not everybody appreciated our restraint.
As explained in this paper, he intentionally focus on the protein and how information cannot get out from there. He remained "discreetly silent" about DNA and RNA, which he was not sure of. The astute reader may also point out about prions, aren't they protein-to-protein information transfer? Yes, but it's not "residue-by-residue transfer of sequential information", but transfer of 3D shape — Crick got that covered. And that is why scientists need to be unambiguous in their language: you may think that we of the ivory tower spoke in something akin to medieval Latin (a.k.a. academic writing), but we do need to transfer our information precisely, or else we will face... 
Third, misunderstandings. I don't know how it looked like in the 1960s, but nowadays information flow in scientific discourse seems to hit the cul-de-sac in bad journalism. Admittedly, there are a lot of papers in which the language is unnecessarily complex and only a few shine in clarity while maintaining precision. That may be one factor, but still, journalists need to put aside the sensationalism, explain our jargons, use a lot of proper analogies; in other words, transferring the information with high fidelity.
Bad journalism, like bad protein, generates more of itself. Both are not good for the brain.

Crick F (1970). Central dogma of molecular biology. Nature, 227 (5258), 561-3 PMID: 4913914

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