Hrincevich+CH+9+student+outline+using+Starr+CH+13

Hrincevich+CH+9+student+outline+using+Starr+CH+13 - Chapter...

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Unformatted text preview: Chapter 9 DNA: The Molecule of Heredity Miescher Discovered DNA • 1868 • Johann Miescher investigated the chemical composition of the nucleus • Isolated an organic acid that was high in phosphorus • He called it “ nuclein ” • We call it DNA (deoxyribonucleic acid) today Mystery of the Hereditary Material • Originally believed to be an unknown class of proteins • Rationale was… – Heritable traits are diverse – Molecules encoding traits must be diverse – Proteins are made of 20 amino acids and are structurally diverse Structure of the Hereditary Material • Experiments in the 1950s showed that DNA is the hereditary material • Scientists raced to determine the structure of DNA • 1953- Watson and Crick proposed that DNA is a double helix Discovery of DNA Funtion: 3 critical experiments Early and puzzling clues • 1928 • Attempting to develop a vaccine • Isolated two strains of streptococcus pneumoniae – Rough strain ( R ) was harmless – Smooth strain ( S ) was pathogenic #1: Griffith Discovers “ Transformation” Griffith Discovers Transformation 1. Mice injected with live cells of harmless strain R. 2. Mice injected with live cells of killer strain S. 3. Mice injected with heat-killed S cells. 4. Mice injected with live R cells plus heat-killed S cells. R S dead S dead S R + dead S dead S X X Mice live No live R cells in their blood Mice die Live S cells in their blood Mice live No live S cells in their blood Mice die Live S cells in the blood Transformation • What happened in the fourth experiment? • The harmless R cells had been transformed by material from the dead S cells • Descendents of the transformed cells were also pathogenic Living R strain Living S strain Heat-killed S strain Living R strain, heat-killed S strain Bacterial strain(s) injected into mouse Results Conclusions • So, what exactly was the transforming material?...
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Hrincevich+CH+9+student+outline+using+Starr+CH+13 - Chapter...

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