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DNA

DNA. The Hereditary Material. The Discovery of DNA. 1869 – Friedrich Miescher investigated chemical composition of DNA using pus cells. At the time, proteins were thought to be hereditary material.

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DNA

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  1. DNA The Hereditary Material

  2. The Discovery of DNA • 1869 – Friedrich Miescher investigated chemical composition of DNA using pus cells. • At the time, proteins were thought to be hereditary material. • Miescher discovered the nuclei of cells contained a substance that does not act like protein. He called this substance nuclein. • This caused debate – Is protein or nuclein the hereditary material?

  3. Location of Hereditary Information • 1930s Hammerling Experiment • Experiment using Acetabularia, one-celled green alga • Hypothesized that hereditary material was found in the foot and possibly the nucleus of the Acetabularia.

  4. Hammerling’s Experiment • Acetabularia Experiment • Observations: • Caps that were removed regrew • Feet that were removed, did not regrow • Caps that grew matched the species of the foot not the stalk. • Conclusions: • Hereditary information was found in the nucleus in the foot of the cell.

  5. The Transforming Principle • The nucleus contains the genetic information but scientists were still uncertain whether the chromosomes consisted of both proteins and DNA. • 1920s - Frederick Griffith was trying to develop a vaccine against pneumonia. He obtained unexpected experimental observations that led him to believe that protein is not the hereditary material. • Griffith Experiment

  6. Some substance (the Transforming Principle) must have been transferred from the dead bacteria to the living non-virulent bacteria making it virulent • 1944 – Avery, McCarty, MacLeod later showed that the Transforming Principle was DNA

  7. Hershey and Chase Experiment • 1952 – Hershey and Chase conducted experiments using bacteriophage T2 that infects a bacterial host. • View experiment Conclusion: DNA, not protein is the hereditary material.

  8. DNA Structure • 1860s - Miesher discovered that nuclein is slightly acidic and composed of large amounts of P and N. • 1920s – Determined that DNA comprises a deoxyribose sugar, a phosphate, and a nitrogen base DNA Structure Animation

  9. DNA Structure Contributors • Chargaff – adenine = thymine, cytosine = guanine • Franklin – X-ray diffraction pattern suggesting a double helix shape • Watson and Crick – Deduced structure of DNA using work of Chargaff, Franklin and Wilkins

  10. DNA Replication and Repair DNA Replicates semi-conservatively

  11. Meselson and Stahl • 1958 - Meselson and Stahl devised an experiment to suggest that DNA replication is semi-conservative. • Meselson and Stahl Experiment • Experiment 2

  12. DNA Replication and Repair DNA Replication is a process comprising of: • Separating DNA strands • Building Complementary Strands • Quality Control DNA Replication Animation

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