Central dogma of molecular biology !

Information flows from DNA to RNA and from RNA to protein; replication copies DNA and reverse transcription goes back from RNA to DNA.

Updated 2026-11-01

Key facts

Replication: DNA → DNA (S phase). Transcription: DNA → RNA (nucleus). Translation: messenger RNA → protein (cytoplasmic ribosomes).
Classic exception: reverse transcriptase copies RNA into DNA (retroviruses such as HIV, and telomerase).
Some RNA viruses copy RNA into RNA with an RNA-dependent RNA polymerase.
One gene can give many proteins thanks to alternative splicing; not every gene ends in a protein (tRNA, rRNA, microRNA).

Scheme (not a metabolic pathway): DNA —replication→ DNA; DNA —transcription→ pre-mRNA —processing→ mRNA —translation→ protein —folding and modification→ active protein.
In eukaryotic cells transcription and translation happen in separate compartments: the mRNA must mature (cap, poly-A tail, splicing) and leave through the nuclear pores.
Bacteria have no nucleus: the ribosome starts translating the mRNA while it is still being transcribed (coupling).
Each step has quality control: DNA polymerase proofreading, nonsense-mediated decay (NMD) of mRNAs with premature stop codons, and chaperones plus the proteasome for misfolded proteins.
Each step is a drug target: fluoroquinolones (bacterial replication), rifampicin (bacterial transcription), aminoglycosides, macrolides and tetracyclines (bacterial translation), nucleoside analogues (HIV reverse transcriptase).

Reverse transcriptase inhibitors block HIV's RNA → DNA step, which human cells do not use for their own genes.
mRNA vaccines deliver a message that ribosomes translate into an antigenic protein, without entering the nucleus or changing the DNA.

Think of the answer, then tap the question to see it.

Which enzyme breaks the usual direction of the central dogma, and in which virus is it typical?

Reverse transcriptase, which copies RNA into DNA; it is typical of retroviruses such as HIV.

Why can translation start before transcription ends in bacteria?

They have no nucleus: the mRNA stays in the cytoplasm and ribosomes translate it while it is being made.

Which human enzyme is a reverse transcriptase?

Telomerase: it uses its own RNA as a template to lengthen telomeres.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Central Dogma (National Human Genome Research Institute (NHGRI), 2026); How do genes direct the production of proteins?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Gene expression (Transcription) (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.