8. Central Dogma -- Part I (1,157)

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Transcription: DNA polymerase (light blue) opens the double helix to make the template strand (dark gray) accessible. It then successively adds RNA nucleotides complementary to the DNA template to build the final mRNA (red). A Poly A tail will be added after the mRNA is released by the RNA polymerase (not shown).

• In 1970, an enzyme called reverse transcriptase was discovered. It used an RNA template to synthesize DNA, enabling information flow from right to left. This is an exception to Crick's claim. And so, today, central dogma diagrams usually acknowledge that relationship by adding a left pointing arrow between DNA and RNA. I've left it out since it's not central to our story.