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Chapter 8: DNA and RNA

Chapter 8: DNA and RNA. Section 8-1: Discovering DNA. The Language of Genes. In order to understand how genes are stored on chromosomes, biologists had to learn the molecule of heredity and the language to interpret the molecular code. Griffith and Transformation.

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Chapter 8: DNA and RNA

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  1. Chapter 8:DNA and RNA Section 8-1: Discovering DNA

  2. The Language of Genes • In order to understand how genes are stored on chromosomes, biologists had to learn the molecule of heredity and the language to interpret the molecular code.

  3. Griffith and Transformation • Frederick Griffith (Britain, 1928) • Studying causes of pneumonia, isolated two types of bacteria from victims – “smooth” and “rough” • Injected mice with both types of bacteria – those injected with smooth bacteria developed pneumonia

  4. Griffith and Transformation • First major experiment – Griffith heated a sample of smooth bacteria, injected it into mice • Result = no pneumonia, concluded heat killed all bacteria

  5. Griffith and Transformation • Second experiment – mixed heat-killed smooth bacteria with harmless rough bacteria • Result = mice developed pneumonia and died • Samples taken from mice showed live, smooth bacteria

  6. Griffith and Transformation • Conclusion – Some molecule or group of molecules had changed harmless rough bacteria into deadly smooth bacteria. • Process called transformation

  7. Avery and DNA • Oswald Avery (Canada, 1944) • Said key to finding molecule of heredity was studying transformation • Hypothesized genes had been transferred in Griffith’s experiments • Conducted experiments in which heat-killed bacteria were treated with enzymes to destroy macromolecules

  8. Avery and DNA • In all cases, transformation still occurred EXCEPT when DNA was destroyed • Conclusion – Genes are made of DNA

  9. Hershey-Chase Experiment • Alfred Hershey and Martha Chase (USA, 1952) • Studied bacteriophages, type of virus that infects bacteria • Attach to outside of bacterium, inject something into bacterium that allow it to make more viruses • Viruses only contain DNA and protein – which ones contains genes?

  10. Hershey-Chase Experiment • Used radioactive isotopes to label viral DNA and protein • Phosphorus-32 used to label DNA, sulfur-35 used to label protein

  11. Hershey-Chase Experiment • Bacteria infected and analyzed - only phosphorus-32 found in infected bacteria • Conclusion – Genetic material of bacteriophage is DNA, not protein.

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