Overview

Francis Crick (who discovered the structure of DNA) coined this term in 1957. It is the fundamental rule of life. Information flows in one direction: from the hard drive (DNA) to the temporary cache (RNA) to the screen (Protein).

Core Idea

The core idea is Information Flow.

  1. DNA: The master copy. Stays safe in the nucleus.
  2. RNA: The working copy. Goes out into the cell.
  3. Protein: The final product. Does the actual work.

Formal Definition

DNA -> (Transcription) -> RNA -> (Translation) -> Protein. Once information has passed into protein, it cannot get out again. (You can’t turn a protein back into DNA).

Intuition

  • DNA: The Architect’s Blueprint (locked in a vault).
  • Transcription: The Foreman makes a photocopy of the blueprint (mRNA).
  • Translation: The Construction Workers (Ribosomes) read the photocopy and build the house (Protein).

Examples

  • The COVID Vaccine (mRNA): It hacks the Central Dogma. We inject mRNA (the photocopy) into your arm. Your cells read it and build the “Spike Protein” of the virus. Your immune system sees the protein and learns to fight it. We skip the DNA step entirely.
  • Retroviruses (HIV): The exception to the rule. HIV carries its info as RNA. It uses an enzyme called “Reverse Transcriptase” to turn its RNA back into DNA and hide it in your genome. It goes backwards.

Common Misconceptions

  • “Dogma” means religious truth: Crick admitted later he used the wrong word. He meant “Hypothesis.” In science, nothing is a dogma.
  • One Gene = One Protein: We used to think this. Now we know about “Alternative Splicing,” where one gene can be chopped up to make many different proteins.
  • Codon: The 3-letter words in the genetic code (e.g., AUG = Start).
  • Ribosome: The machine that reads RNA and builds protein. It is the universal constructor found in every living thing.

Applications

  • Biotechnology: Almost all genetic engineering relies on manipulating this flow (e.g., blocking transcription to stop a disease).

Criticism / Limitations

  • Epigenetics: Challenges the simplicity of the dogma by showing that the “software” (DNA) can be modified by the “hardware” (proteins/environment).
  • Prions: Proteins that transmit information to other proteins without DNA/RNA. This breaks the rule.

Further Reading

  • Crick, Francis. What Mad Pursuit. 1988.
  • Watson, James. The Double Helix. 1968.