Presentation Transcript

1. A Brief History of DNA
2. Discovered??? In 1869 Johann Miescher discovered DNA, but he really didn’t exactly know what it was. He discovered “nuclein” a phosphorus/nitrogen rich substance . He isolated this nuclein from pus-filled bandages. He actually found the DNA in white blood cells. He called the substancenuclein since it was derived from the nucleus. It took 84 years until it was understood that DNA was the genetic material for life.
3. What is the Hereditary Molecule? In 1920, Fredrich Griffith discovered the “transforming factor”. Griffith concluded that a harmless strain of bacteria could be made “deadly” by mixing it with dead dangerous bacteria. The dead dangerous bacteria passed on its characteristics to the harmless strain. Griffith hypothesized that proteins were the molecule of heredity.
4. I just wanted to let you all know that I have discovered this phenomenal new process called TRANSFORMATION. Apparently, if a deadly bacterial cell is killed, it can't cause a disease. But if it is put in the same tube as live, but harmless bacterium, then somehow the live bacteria can now spread the disease.
5. The Debate In 1944 Oswald Avery suggested that DNA, not protein was responsible for heredity. It was known that both proteins and nucleic acids were found in the nucleus. When Oswald exposed nuclei to protein destroying enzymes bacteria still experienced transformation. When Oswald exposed nuclei to DNA destroying enzymes, they did not transform. Unfortunately many other scientists refused to believe Avery; DNA seemed so insignificant compared to protein.
6. Hershey and Chase Confirm In 1952 Alfred Hershey and Martha Chase set out to prove that Avery was correct stating that DNA was the molecule of heredity. Instead of bacteria, they used viruses to prove that DNA transforms bacteria.
7. Viruses, otherwise known as a bacteriophage needs a host to replicate, so it takes over a bacteria cells DNA. When the protein portion of the bacteriophage was labeled, transfer of material was not visible within the cells. When the phosphorus DNA was labeled the transfer was radioactively visible. This proved DNA was the molecule that carried genetic blueprints for life!
8. Erwin Chargaff In 1950 Erin Chargaff proposed that in any organism, the amount of guanine is equal to that of cytosine, and the amount of adenine is equal to thymine. A = T and C = G.
9. Rosalind Franklin Rosalind Franklin is best known for her work determining the shape of DNA using x-ray diffraction images. She showed that DNA has a helical shape. Her work greatly assisted Watson and Crick in their model.
10. Watson and Crick: The Model American geneticist James Watson and English physicist Francis Crick, with much help from a scientist named Rosalind, figured out why the ratios were important to the structure of DNA.  Franklin's data on the shape of the DNA molecule revealed its structure of the double helix; in a great controversy, Watson and Crick scooped Franklin's information and, using Chargaff's rules, cracked the code on the structure of DNA. The won the Nobel prize for their contribution to science.