Read the Experiments that Identified Genetic Material
Experiments separated transformation, chemical identity and the molecule that enters a cell; RNA’s catalytic capacity also informs origin-of-life models.
Genetic Material and Its Discovery is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Follow the evidence chronologically
Griffith showed transformation; Avery, MacLeod and McCarty identified DNA as the transforming principle; Hershey and Chase used 32P-labelled DNA and 35S-labelled protein to show DNA enters bacteria; Watson and Crick proposed the double helix. Kornberg is associated with DNA polymerase, not the lac operon.
Why DNA stores information well
DNA’s deoxyribose and thymine make it chemically more stable than RNA, and a complementary strand supports repair. RNA can both store information and catalyse reactions, making an RNA-world stage plausible.
Read the Hershey–Chase evidence
Sulfur-35 labels phage protein, which remains with the empty phage coats; phosphorus-32 labels DNA, which enters bacterial cells. Production of progeny after infection with purified phage DNA is independent evidence that DNA carries heritable information.
OlympIQ exam lens
- ✓Griffith → Avery–MacLeod–McCarty → Hershey–Chase → Watson–Crick.
- ✓32P labels DNA; 35S labels protein.
- ✓DNA is stable storage; RNA can store and catalyse.
A label must distinguish the candidate molecules; tritium would label both DNA and protein.
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