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

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Presentation transcript:

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 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

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

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

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

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

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

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?

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

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