American Masters

This body. What is it? How did it begin? The discovery of DNA itself as the hereditary material is not the discovery of Watson and Crick About the time that Darwin published the "Origin of Species" a Swiss German scientist named Friedrich Miescher was looking for a project and his advisor said see if you can find out anything about the nucleus. Miescher went down to the local hospital and got some bandages from patients and scraped off the pus because that was a great source of white blood cells and each one of those has a nucleus so we had a little vial of cell nuclei ground him up and did chemical tests and he discovered in the cell nucleus this new material, he didn't know what it was... he discovered DNA But DNA is not yet thought of as the material of the chains it's still pus on a bandage. We knew by about 1910 that genes were associated with chromosomes. Chromosomes were known to be made of the DNA and protein. It wasn't clear which one was the hereditary material. Protein is most of the interesting stuff that goes on in tissue, muscle, blood, sinew, organs... around the turn of the century a number of people studied the biochemistry of DNA found out that it has these four subunits, protein has 20 or more different building blocks so it seemed obvious that protein was a more complicated molecules so probably it was the material of the gene. Then in 1944 out of left field came an experiment that changed the game. Avery MacLeod and McCarty did an eloquent experiment with the bacterium pneumococcus The bacteria that caused pneumonia. There were different strains of the bacteria and one of those strains was virulent, meaning it caused the disease. Then you had another form of the bacteria it was non-virulent. Oswald Avery showed that you could convert the benign form into a virulent form when the only thing exchanged is DNA. These bacteria when they divided their descendants could be killers too. This therefore was definitive evidence that DNA was the molecule of heredity.