Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
15-02-10 Friedrich Miescher DNA: The History of Its Understanding Mr. Masri SBI4U Humberside C.I. • Investigated the contents of pus cell nuclei • Pus cells are readily available from infectious patients. • Found that the nuclei contained a significant amount of material that was NOT protein • Called it nuclein, but it was later named DNA Frederick Griffith • done in 1928 - tried to develop a vaccine against pneumoniae • worked with 2 types of streptococcus pneumoniae: Strain R (rough) S (smooth) Characteristics • no capsule • non-pathogenic • w/ capsule • pathogenic Griffith… • Injected different bacteria into four groups of mice: Group Mice Result # Injected w/ 1 R Mice lives, unaffected 2 S Mice die (from pneumonia) 1 15-02-10 Griffith… Group Mice Result # Injected w/ 3 4 Heat killed S Mice live, unaffected Heat killed Mice die S + Live R • Blood sample from mice group #4 contained live smooth bacteria Griffith… Griffith’s Conclusion: • R cells had acquired from the dead S cells the ability to make the polysaccharide capsule • the bacteria underwent transformation - the transfer of genetic material from one bacterium to another through the liquid in which the bacteria live 2 15-02-10 Griffith… • Avery, McCarty and MacCleod (early 1940s) furthered Griffith's work and also identified DNA as being the transforming agent Joachim Hammerling • Conducted experiments on Acetabularia, a one celled green algae • Hypothesized that hereditary information is stored in the nucleus Joachim Hammerling Why study algae? • Three distinct parts: a 'foot' that has the nucleus, a stalk and a cap region. • Not microscopic, can grow to 5cm in length. 3 15-02-10 Joachim Hammerling Alfred Hershey and Martha Chase If he removed the cap, the cap grew back. If he removed the foot, it did not. Concluded the instructions for making the cap were in the foot – possibly the nucleus. He repeated his experiment and got the same results. Hershey and Chase Hershey and Chase… • In 1952, they used radioactively labeled bacteriophage (virus) to infect bacterial cells • Virus is made up of two parts: DNA and a protein coat • DNA contains phosphorous but no sulfur. • Protein contains sulfur, but no phosphorus. • No one knew for certain which became injected into the host cell and was involved in the creation of new viruses. • Hershey and Chase radiolabelled viral proteins with S-35 and viral DNA with P-32. • These radioisotopes are very unstable and easy to measure the radioactive decay. 4 15-02-10 Hershey and Chase… • The viruses were allowed to infect the bacterial hosts. • Only P-32 was present in the bacterial cells - No S-35 Conclusion: • DNA, NOT protein, is the hereditary material 5