The Central Dogma of Molecular Biology
Coined by Francis Crick in 1958, the central dogma describes the two-step process, transcription and translation, by which the information in genes flows into proteins: DNA → RNA → protein.
1. Transcription (DNA → RNA)
RNA polymerase reads the DNA template strand in the 3' to 5' direction to synthesize a complementary mRNA molecule in the 5' to 3' direction.
2. mRNA Processing (Eukaryotes)
Before leaving the nucleus, pre-mRNA undergoes:
- 5' Capping (7-methylguanosine)
- 3' Poly-A Tail addition
- Splicing (removal of introns via the spliceosome)
3. Translation (RNA → Protein)
Ribosomes read the mRNA transcript in triplets (codons). tRNAs bring the corresponding amino acids, building the polypeptide chain.
Exceptions to the Rule
Retroviruses (like HIV) use Reverse Transcriptase to synthesize DNA from an RNA template (RNA → DNA), directly violating the original simplified dogma.