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• First isolated nucleic acids, naming them “nuclein.” This discovery revealed DNA as a new substance, laying the foundation for understanding genetics.

Frederick Miescher (1869) – Discovery of nuclein (DNA)

• National Library of Medicine: Miescher and DNA

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• Discovered the “transforming principle” through experiments with bacteria, demonstrating that genetic information could transfer between organisms.

Frederick Griffith (1928) – Discovery of the transforming principle

• Nature: Griffith’s Experiment

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• Confirmed Griffith’s findings by identifying DNA specifically as the genetic material responsible for inheritance.

Oswald Avery (1944) – DNA identified as the genetic material

• Cold Spring Harbor Laboratory: Avery’s Experiment

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• Created Chargaff’s Rules, discovering equal amounts of adenine/thymine and cytosine/guanine in DNA, crucial for determining DNA’s structure.

Erwin Chargaff (1950) – Base-pairing rules (A=T, C=G)

• Cold Spring Harbor Laboratory: Chargaff’s Rules

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• Suggested structural models for DNA and proteins. Although his triple-helix DNA model was incorrect, his ideas encouraged others to investigate further.

Linus Pauling (1951-1953) – Triple-helix DNA model (incorrect) and protein structure discoveries

• Linus Pauling and the DNA Structure

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• Conducted the Hershey-Chase experiment, using viruses to confirm DNA, not protein, was genetic material.

Martha Chase and Alfred Hershey (1952) – Hershey-Chase Experiment proving DNA is the genetic material

• Nature: Hershey-Chase Experiment

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• Captured Photo 51 through X-ray crystallography, providing key evidence of DNA’s double-helix structure.

Rosalind Franklin (1952) – X-ray diffraction image of DNA (Photo 51)

• PBS: Rosalind Franklin and DNA

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• Developed the first accurate double-helix DNA model, explaining how genetic information is stored and replicated.

James Watson and Francis Crick (1953) – DNA’s double-helix model

• Cold Spring Harbor Laboratory: Watson and Crick’s Discovery