28 September 2017

Anniversary of "dogma"

Daria Spasskaya, N+1, based on the article 60 years ago, Francis Crick changed the logic of biology (M.Cobb, PLOS Biology, 2017).

In September 1957, Francis Crick first published a hypothesis concerning how the realization of hereditary information encoded in DNA occurs. In short, it can be formulated as follows: the flow of information is carried out from DNA to proteins (via RNA) and never in the opposite direction.

Crick himself, a future Nobel Prize winner who received it for discovering the structure of DNA, called this hypothesis "the central dogma of molecular biology." As it turned out later, he did not know the meaning of the word "dogma" well and used it by accident – the scientist could not give almost any experimental evidence in favor of his reasoning at that time. However, time has shown that Crick was right in his categoricality.

Now this statement seems trivial: already at school in biology lessons they learn that hereditary information is encoded in DNA, transmitted from cell to cell by DNA replication and implemented through matrix RNA into proteins by decoding the genetic code.

Proteins perform almost all the basic functions in a living cell. These complex molecules are synthesized on ribosomes, which use a sequence of matrix RNA as instructions, and amino acids as building blocks.

The correct decoding of the matrix RNA sequence is provided by special adaptive RNA molecules – transport RNAs. At one end, these molecules contain a triplet of nucleotides called an anticodon – it is complementary to the triplet codon in RNA (and DNA), and at the other end – a certain amino acid. The rule that determines which codons correspond to which amino acid is called the genetic code.

These principles are universal for almost all living organisms on Earth (some exceptions may be RNA viruses whose hereditary information is encoded in RNA, but the principles of protein synthesis and genetic code work for them as well).

All this was not known at the time when Crick gave his lecture at the Society for Experimental Biology symposium at King's College London in 1957.


Four years earlier, Francis Crick, James Watson and colleagues had deciphered the structure of DNA, but no one really knew why DNA was needed and what it did. It was only in the 40s that there was confirmation that DNA plays the role of a carrier of information in the cell.

How hereditary information is realized, how genes work, how protein synthesis occurs – scientists intensively searched for answers to these questions in the 50s - 60s of the XX century. It can be said that Crick found these answers in advance, based on theoretical reasoning and having very little experimental data on hand.

In his lecture, which was published already in 1958 under the title "On protein synthesis", Crick essentially formulated all the basic principles of molecular biology formulated above. He claimed that DNA serves as a matrix for an intermediate RNA molecule – the existence of such an "intermediate" was proved only in the early 60s. The intermediate RNA, in turn, serves as an instruction for the synthesis of proteins on ribosomes – microsomal bodies, as they were then called. Crick also predicted the existence of an adaptive molecule, tRNA, which was discovered "in vitro" only a year later. He also touched upon the principles of the genetic code, which were not known at that time.

The "central dogma" itself is represented in the photo of the draft of the Cry, which has not been published.


It states that the flow of information can be carried out as follows: from DNA to DNA, from DNA to RNA, from RNA to proteins and from RNA to RNA. The cry also allowed the transition from RNA to DNA, but "prohibited" the transfer of information in the cell from protein to nucleic acids.

As subsequent experiments showed, he was right: at present we know both the processes of RNA replication and reverse transcription – DNA synthesis on an RNA matrix, but no one has shown DNA synthesis on a protein matrix so far, so "dogma" remains dogma.

Portal "Eternal youth" http://vechnayamolodost.ru  28.09.2017

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