Central Dogma of Molecular Biology

The Central Dogma of Molecular Biology, first described by Francis Crick in 1958, is a model describing the flow of genetic information in living cells; from the language of nucleic acids (nucleobases) to that of proteins (amino acids). The dogma is concerned with "[...] the residue-by-residue transfer of sequential information. It states that information cannot be transferred back from protein to either protein or nucleic acid."

Diagrammatically, it can be represented as such:

external image 160px-Centraldogma_nodetails.GIF

DNA replication , transcription and translation are considered the processes common to all cellular life (these are represented by the blue arrows in the diagram). Reverse transcription (RNA --> DNA) and RNA replication are rarer, although both have been found to occur in eukaryotic cells (for instance in the case of retrotransposons) as well as in viruses with an RNA genome. These rarer processes are represented by the red arrows.

Direct 'reverse translation' from protein to DNA has been observed in vitro, in cell-free systems, although is yet to be seen in any cellular or viral life. Protein --> protein transfers have been considered in the case of prions; however, prions only induce conformational changes in neighbouring proteins and not sequential changes, so they are not typically considered an exception to the dogma. For this reason, neither protein --> DNA, nor protein --> protein interactions are accepted and thus, according to Crick's reevaluation of the dogma in the 1970s, the case remains that sequential transfer of information does not naturally occur from the starting point of proteins.