Biology › Section G · Chromosomes and DNA › Topic G.3
Discovering DNA and its structure
For nearly a century after its discovery, DNA was dismissed as too simple to carry heredity — proteins looked the likelier library. A chain of elegant experiments overturned that: Griffith's dead bacteria that killed, Avery's enzymes, Hershey and Chase's radioactive phage, Chargaff's suspiciously paired ratios. Then one X-ray photo let Watson, Crick, and Franklin's data reveal the double helix — and its structure immediately explained how it copies and stores information.
In this topic
- Nuclein: the first isolation
- Griffith's transformation experiments (1928)
- Avery, MacLeod, and McCarty: the elimination
- Hershey and Chase: the decisive phage
- Worked example: reading the Hershey-Chase tubes
- Chargaff's rules
- The nucleotide: DNA's building block
- The double helix: Franklin's photo, Watson and Crick's model
- Helix dimensions and grooves
- Worked example: Chargaff arithmetic
- Common mistakes to avoid
- Key takeaways
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