Central dogma of molecular biology Totally Explained

Everything about The Central Dogma Of Molecular Biology totally explained

The central dogma of molecular biology was first enunciated by Francis Crick in 1958 and re-stated in a Nature paper published in 1970:
ť The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information can't be transferred back from protein to either protein or nucleic acid.

In other words, 'once information gets into protein, it can't flow back to nucleic acid.'
The dogma is a framework for understanding the transfer of sequence information between sequential information-carrying biopolymers, in the most common or general case, in living organisms. There are 3 major classes of such biopolymers: DNA and RNA (both nucleic acids), and protein. There are 3×3 = 9 conceivable direct transfers of information that can occur between these. The dogma classes these into 3 groups of 3: 3 general transfers (believed to occur normally in most cells), 3 special transfers (known to occur, but only under specific conditions in case of some viruses or in a laboratory), and 3 unknown transfers (believed to never occur). The general transfers describe the normal flow of biological information: DNA can be copied to DNA (DNA replication), DNA information can be copied into mRNA, (transcription), and proteins can be synthesized using the information in mRNA as a template (translation).

Methylation

Variation in methylation states of DNA can alter gene expression levels significantly. Methylation variation usually occurs through the action of DNA methylases (which are proteins). When the change is heritable, it's considered epigenetic. When the change in information status isn't heritable, it would be a somatic epitype. The effective information content has been changed by means of the actions of a protein or proteins on DNA, but the primary DNA sequence isn't altered.

Prions - almost an "unknown transfer"

Prions are proteins that propagate themselves by making conformational changes in other molecules of the same type of protein. This change affects the behaviour of the protein. In fungi this change happens from one generation to the next, for example Protein → Protein. Although this represents a transfer of information, it isn't an exception to the central dogma, since the sequence of the protein remains unchanged; but it's the exception when you see the central dogma as describing nucleic acid as the central form of replicative information (the protein-only hypothesis).

Use of the term "dogma"

In his autobiography, What Mad Pursuit, Crick wrote about his choice of the word dogma and some of the problems it caused him: ť I called this idea the central dogma, for two reasons, I suspect. I'd already used the obvious word hypothesis in the sequence hypothesis, and in addition I wanted to suggest that this new assumption was more central and more powerful. ... As it turned out, the use of the word dogma caused almost more trouble than it was worth.... Many years later Jacques Monod pointed out to me that I didn't appear to understand the correct use of the word dogma, which is a belief that can't be doubted. I did apprehend this in a vague sort of way but since I thought that all religious beliefs were without foundation, I used the word the way I myself thought about it, not as most of the world does, and simply applied it to a grand hypothesis that, however plausible, had little direct experimental support.

Similarly, Horace Freeland Judson records in The Eighth Day of Creation:

"My mind was, that a dogma was an idea for which there was no reasonable evidence. You see?!" And Crick gave a roar of delight. "I just didn't know what dogma meant. And I could just as well have called it the 'Central Hypothesis,' or — you know. Which is what I meant to say. Dogma was just a catch phrase."

Criticisms of the use of the central dogma as a research strategy

Some researchers in the area of systems biology claim that scientists sometimes misuse the central dogma as a research strategy. They claim that an uncritical reading of the central dogma could inhibit novel approaches to understanding multicellular development of organisms as well as multicellular diseases; that the central dogma is often used as a reductionist research strategy that proceeds bottom up, attempting to explain all biological phenomena in molecular terms. Although they don't dispute the very specific reading of the central dogma, these researchers claim that a reductionist research strategy may limit the understanding of complex systems that can't be analyzed by their molecular interactions alone because of the combinatorial complexity involved.

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