DNA The universal molecule of life Discovery of

Discovery of DNA - Miescher • First isolated 1869 • Johannes Friedrich Miescher •

Discovery of DNA - Levene • Phoebus Levene • 1919 discovery DNA consists of

Discovery of DNA - Griffith • Frederick Griffith • 1928 • First clear evidence

Griffith’s experiment • Streptococcus pneumoniae – Two strains • Smooth (S strain) surrounded by

Griffith’s experiment Infected with R strain

Griffith’s experiment Infected with S strain

Griffith’s experiment • Heat treat S strain

Griffith’s experiment S strain Heat treated

Griffith’s experiment Infected with S strain Heat treated

Griffith’s experiment • Heat treated S strain plus • Live R strain

Griffith’s experiment R strain plus heat treated S strain

Griffith’s experiment Infected with R strain plus heat treated S strain

Griffith’s experiment • Examination of dead mice injected with R/S mixture • All bacteria

Discovery of DNA – Avery • Oswald Avery • 1887 -1955 • Expanded Griffith’s

Discovery of DNA – Chargaff • Erwin Chargaff • 1905 -2002 • Used chromatography

Discovery of DNA – Chargaff’s Rules 1. In natural DNA the number of guanine

Discovery of DNA – Watson & Crick • James D Watson • Francis Crick

Discovery of DNA – Franklin • Rosalind Franklin • 1920 -1958 • X-ray crystallographer

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DNA The universal molecule of life

Discovery of DNA - Miescher • First isolated 1869 • Johannes Friedrich Miescher • Extracted chemical from nucleus containing phosphorus, nitrogen, and sulfur

Discovery of DNA - Levene • Phoebus Levene • 1919 discovery DNA consists of units of a base, sugar and phosphate

Discovery of DNA - Griffith • Frederick Griffith • 1928 • First clear evidence that DNA carried genetic • information

Griffith’s experiment • Streptococcus pneumoniae – Two strains • Smooth (S strain) surrounded by a capsule • Rough (R strain) no capsule

Griffith’s experiment R strain

Griffith’s experiment Infected with R strain

Griffith’s experiment S strain

Griffith’s experiment Infected with S strain

Griffith’s experiment • Heat treat S strain

Griffith’s experiment S strain Heat treated

Griffith’s experiment Infected with S strain Heat treated

Griffith’s experiment • Heat treated S strain plus • Live R strain

Griffith’s experiment R strain plus heat treated S strain

Griffith’s experiment Infected with R strain plus heat treated S strain

Griffith’s experiment • Examination of dead mice injected with R/S mixture • All bacteria now S strain • Griffith killed during London blitz • Years later shown that DNA had passed from killed S to R strain.

Discovery of DNA – Avery • Oswald Avery • 1887 -1955 • Expanded Griffith’s experiment • Showed that DNA was the chemical responsible for inheritence

Discovery of DNA – Chargaff • Erwin Chargaff • 1905 -2002 • Used chromatography to determine ratios of nucleotides in DNA

Discovery of DNA – Chargaff’s Rules 1. In natural DNA the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units. 2. The composition of DNA varies from one species to another, in particular in the relative amounts of A, G, T, and C bases.

Discovery of DNA – Watson & Crick • James D Watson • Francis Crick • 1953 suggested DNA’s structure based on Franklin’s data.

Discovery of DNA – Franklin • Rosalind Franklin • 1920 -1958 • X-ray crystallographer