Central dogma of molecular biology

Basic formulation and routine processes

At its simplest, the central dogma summarizes three routine transfers of sequence information in cells: DNA → DNA (copying of DNA), DNA → RNA (making an RNA copy) and RNA → protein (using RNA to specify protein sequence). Each of these corresponds to well-studied molecular processes: DNA replication, transcription and translation. The term sequence or information in this context means the linear order of nucleotide bases or amino acids that determines biological function and heredity.

Classification of possible transfers

Crick and subsequent authors classified the nine conceivable direct transfers among the three polymer types — DNA, RNA and protein — into three groups:

• General transfers: routinely occurring in cells (DNA→DNA, DNA→RNA, RNA→protein).
• Special transfers: observed in particular biological contexts or experimentally (for example RNA→DNA by reverse transcription in retroviruses; RNA→RNA replication in RNA viruses).
• Transfers not observed as templated processes: direct templated information transfer from protein→nucleic acid or protein→protein as a way to encode nucleotide sequence is not supported by evidence.

Nine conceivable direct transfers (examples)

1. DNA → DNA: replication of the genome during cell division (DNA replication).
2. DNA → RNA: transcription of genes to produce mRNA, tRNA and rRNA (transcription).
3. RNA → protein: decoding mRNA into amino acid sequence during translation.
4. RNA → RNA: replication of RNA genomes in many RNA viruses.
5. RNA → DNA: reverse transcription carried out by reverse transcriptase in retroviruses and retrotransposons.
6. DNA → protein: indirect in most cases (information passes DNA→RNA→protein rather than DNA directly templating protein sequence).
7. Protein → protein: conformational templating (e.g., prion propagation) changes protein state but does not encode nucleotide sequence.
8. Protein → RNA and 9) Protein → DNA: no general mechanism is known by which a protein sequence acts as a template to create a specific nucleic acid sequence; such transfers are classified as not occurring under normal biological mechanisms.

Historical context and scope

Crick first described the idea in the late 1950s and restated it later to emphasize that it concerns the transfer of sequence information rather than forbidding any biochemical influence of proteins on nucleic acids. The dogma refines an older conceptual separation between hereditary and somatic material called the Weismann barrier, which argued that hereditary information in the germline passes to somatic cells and not vice versa. In molecular terms, the dogma helps clarify the distinct roles of nucleic acids (DNA and RNA) and proteins in storing and acting on biological information; it also frames the concept of a gene as a sequence-bearing unit that can be expressed into a functional product.

Exceptions, refinements and modern perspective

Subsequent discoveries expanded the original account without negating its core insight. The existence of reverse transcriptase showed that information can move from RNA back to DNA under particular biological circumstances; RNA viruses replicate RNA genomes directly; and many noncoding RNAs regulate gene expression without encoding protein. Epigenetic marks and regulatory feedbacks alter how sequence information is used without changing the underlying nucleotide sequence itself. Importantly, although proteins can influence nucleic acid metabolism (for example, enzymes that edit or modify DNA and RNA), there is no established templated mechanism in which a specific protein sequence encodes and transfers its sequence information into a nucleic acid sequence.

Importance and applications

The central dogma remains a practical organizing principle in genetics, molecular biology, biotechnology and medicine. It underpins how scientists connect gene sequence to gene product and phenotype, informs experimental design in cloning and sequencing, and guides understanding of viral replication, gene expression technologies and therapeutic strategies that intervene at the levels of DNA, RNA or protein.

For historical and technical introductions, see treatments of Crick and accessible reviews of the structures and mechanisms of the DNA helix, DNA, RNA and proteins.