Chapter 8 DNA and RNA Section 8 1
- Slides: 11
Chapter 8: DNA and RNA Section 8 -1: Discovering DNA
The Language of Genes l 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 l l l 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 l l 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 l l l 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 l l Conclusion – Some molecule or group of molecules had changed harmless rough bacteria into deadly smooth bacteria. Process called transformation
Avery and DNA l l 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 l In all cases, transformation still occurred EXCEPT when DNA was destroyed l Conclusion – Genes are made of DNA
Hershey-Chase Experiment l l Alfred Hershey and Martha Chase (USA, 1952) Studied bacteriophages, type of virus that infects bacteria – l 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 l Used radioactive isotopes to label viral DNA and protein l Phosphorus-32 used to label DNA, sulfur-35 used to label protein
Hershey-Chase Experiment l Bacteria infected analyzed - only phosphorus-32 found in infected bacteria l Conclusion – Genetic material of bacteriophage is DNA, not protein.