1. DeoxyriboNucleic Acid The Blueprint of Life

2. Who discovered DNA? • Swiss chemist Friedrich Miester in 1869 • Nobody cared

3. Assumption of the Time • Proteins were well-known and assumed to be the genetic carrier • Lots of different proteins discovered, 20 different amino acids

4. Phoebus Levene (1910s) • Russian biochemist who studied DNA, or nuclein as it was originally called • Discovered structure of nucleotides and • the presence of 4 unique DNA nucleotides

5. Nucleotide Structure

6. How Did We Determine DNA was the Genetic Material? • Two major sets of experiments conducted over 20-30 years • Avery, MacLeod and McCarty (1944) • Hershey and Chase (1952)

7. Avery, MacLeod, McCarty • Tried to explain the findings of Frederick Griffith in 1928

8. Griffith’s Experiment • Passage of a substance could transform harmless bacteria into deadly virulent bacteria

9. Avery, MacLeod + Griffith • Demonstrated that transformation occurred when proteins were removed • Transformations did not occur when DNA was removed • Thus it was the DNA responsible for transforming a bacteria

10. Avery, MacLeod and McCarty

11. Alfred Hershey and Martha Chase • Tried to explain how bacteriophages invaded bacteria and changed their behavior • It was known that bacteriophages consisted of proteins and DNA

12. Results of Hershey Chase

13. Erwin Chargaff • Species differed in the number of each nucleotide they contained • The number of As and Ts was usually similar, same with Gs and Cs

14. Rosalind Franklin and Maurice Wilkins • Used a technique called X-Ray Crystallography to study shape

15. The X-Ray Image • Demonstrated that the shape of DNA was a double helix, with the nitrogenous bases on the inside • She independently discovered the structure of DNA

16. They Did Her Dirty • Her X-Ray image was shown to other scientists (including Watson and Crick) without her permission • Watson and Crick used the X-Ray and some of Franklin’s earlier work to suggest the double helix model of DNA • She died at 37 so we’ll never know if she would have shared in their Nobel Prize 

17. James Watson and Francis Crick

18. Watson and Crick • Published their model in a 1 page paper • Literally had made models out of cardboard until one fit

20. Key Points in the Model • DNA is double stranded in a double helix • Strands are held together by H-bonds between nitrogenous bases • A-T 2 hydrogen bonds • G-C 3 Hydrogen bonds • Backbone is made up of alternating sugar and phosphate • DNA strands are anti-parallel (run in opposite directions)

22. DNA Model • Working in groups you will design and build a simple model of DNA • It should demonstrate the 4 key points of the Watson/Crick model • Can be made out of anything. Should have something representing Phosphate, Sugar, each of the 4 bases and H-bonds (the correct number) • Due Monday