First articulated by Francis Crick in 1958, the central dogma describes the unidirectional flow of genetic information: DNA is transcribed into RNA, which is then translated into proteins. Though the model has been refined—especially with the discovery of introns and alternative splicing—the fundamental principle that DNA serves as the master blueprint remains unchallenged.
In eukaryotic cells, the DNA double helix is confined to the nucleus. Transcription begins when RNA polymerase binds to the promoter region and unwinds the DNA strands, synthesizing a complementary RNA copy from the template strand. This nascent transcript, called pre‑mRNA, contains both exons (coding sequences) and introns (non‑coding sequences).
After transcription, the pre‑mRNA undergoes splicing: introns are excised and exons are ligated to form mature messenger RNA (mRNA). The mature mRNA exits the nucleus and is ready for translation.
mRNA carries the nucleotide sequence that encodes a specific protein. The genetic code consists of four nitrogenous bases—guanine (G), cytosine (C), adenine (A), and thymine (T) in DNA, replaced by uracil (U) in RNA. Each codon, a triplet of bases, specifies one of the 20 standard amino acids or a start/stop signal.
Ribosomes are the cellular machines that translate mRNA into polypeptide chains. A ribosome consists of a small subunit that reads the mRNA and a large subunit that links amino acids. Ribosomes are either free in the cytosol—producing cytosolic proteins—or bound to the rough endoplasmic reticulum, directing secretory and membrane proteins toward the extracellular space.
During translation, transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome. Each tRNA has an anticodon that matches a specific mRNA codon, ensuring the correct amino acid is incorporated. The ribosome catalyzes peptide bond formation, elongating the nascent polypeptide until a stop codon signals termination.
The completed polypeptide undergoes folding and post‑translational modifications to become a functional protein.
Alternative splicing allows a single gene to generate multiple protein isoforms by varying which exons are joined together. Introns, while non‑coding, can influence gene regulation and serve as sources for novel genetic elements. Thus, the central dogma remains a linear framework, but the cellular reality is enriched by layers of complexity that expand proteomic diversity.
In summary, the central dogma remains a cornerstone of molecular biology: DNA → RNA → Protein. The processes of transcription, mRNA processing, translation, and alternative splicing together orchestrate the precise expression of genes in living organisms.
