The central dogma of molecular biology describes the directional flow of genetic information: DNA sequences are transcribed into RNA molecules, which are then translated into polypeptides.
Explanation
The central dogma, first articulated by Francis Crick in 1958, frames the standard pathway by which genetic information is expressed within cells. In its simplest form, it describes how the nucleotide sequence in DNA is copied into a complementary sequence of ribonucleic acid (RNA) through transcription. This messenger RNA serves as a template for the synthesis of proteins during translation, where ribosomes read codons and assemble amino acids into polypeptide chains. DNA replication ensures that genetic information is accurately passed to daughter cells during cell division, but the central dogma focuses on information flow rather than copying. Crick also pointed out that sequence information cannot be transferred from protein back to nucleic acid, because protein sequences do not act as templates for nucleic acid synthesis. This directionality has important implications for evolution and heredity, as genetic information is preserved at the level of nucleic acids and not altered by the proteins it encodes.
The concept underscores the relationship between nucleic acids and proteins and provides a scaffold for understanding gene expression, regulation, and mutation. By separating information storage (DNA), intermediate messaging (RNA), and functional output (protein), the dogma aids in tracing how genetic variants manifest as phenotypic traits. Although most organisms follow this pathway, some exceptions exist. Retroviruses, such as human immunodeficiency virus, use reverse transcriptase to convert RNA back into DNA, integrating viral genomes into host chromosomes. In addition, certain RNA molecules like ribozymes perform catalytic roles without translation. These cases are viewed as specific mechanisms rather than contradictions, and the central dogma remains a foundational principle in molecular biology.
Key Processes and Exceptions
Replicative examples of the central dogma are seen in bacteria, plants and animals where DNA replication, transcription and translation operate continuously. In prokaryotes, transcription and translation occur concurrently in the cytoplasm, enabling rapid protein synthesis from operons such as those controlling lactose metabolism. In eukaryotes, transcription takes place in the nucleus, and pre-mRNA undergoes splicing to remove introns before translation in the cytoplasm. The genetic code, with its start and stop codons, provides a universal basis for translation across species.
Important exceptions highlight the flexibility of information flow. Retroviruses carry RNA genomes and encode reverse transcriptase to synthesize complementary DNA from RNA, which is then inserted into host DNA. Hepadnaviruses such as hepatitis B also use reverse transcription in their replication cycle. In addition, prions are infectious proteins that propagate by inducing misfolding in normal proteins, illustrating a protein-to-protein transfer of structural information without nucleic acid involvement. These examples expand our understanding but do not negate the core principle that nucleic acids drive protein synthesis.
The central dogma remains a guiding framework for molecular genetics. It links the storage of hereditary information to the synthesis of functional proteins and helps explain how genetic variation results in biological diversity. While special cases and regulatory mechanisms add complexity, the fundamental pathway from DNA to RNA to protein remains central to our understanding of life processes.
Related Terms: DNA replication, Transcription, Translation, Gene Expression, Reverse Transcriptase