1. The History of DNA
Page
Page 279 Questions 1, 2, 4, 8

2. 1920 – What is the heredity molecule?
Importance of Mendel’s work.
Scientists were mostly sure that proteins were the genetic material
Why not DNA?

3. Nucleotide Pattern

4. 1920 – What is the heredity molecule?
Importance of Mendel’s work.
Scientists were mostly sure that proteins were the genetic material
Why not DNA?
Why did they think it was proteins?

5. 1928 – Frederick Griffith smooth S-strain = virulent
Studied two strains of Pneumococcus bacteria
rough R-strain = non-virulent
smooth S-strain = virulent

7. Griffith’s Experiment

8. Griffith Experiment Conclusions
Some “factor” from the dead, virulent smooth strain “transformed” the living, non-virulent rough strain.
What was their conclusion?

9. nucleus at bottom of stalk
1930 – Joachim Hammerling
Acetabularia – type of alga
nucleus at bottom of stalk

10. Hammerling’s Experiment #1
no regrowth

11. Hammerling’s Experiment #2
What was his conclusion?

12. 1944 – Avery, McCarty & MacLeod
Continued Griffith’s work with virulent Pneumococcus
Tested three conditions:
s strain + protease
s strain + RNase
s strain + DNase

14. Avery, McCarty & MacLeod Experiment Conclusion
What do the results of this experiment mean?

15. 1940s – Edwin Chargaff
Studied concentrations for each of the four nucleotides.
Chargaff’s Rule?
Question that will be on the quest: Why are organisms with a higher percentage of G’s and C’s generally more complex?

16. 1952 – Hershey & Chase
Studied bacteriophage (a bacterial virus) used to infect bacteria

17. Hershey & Chase Experiment

18. 1950s – Maurice Wilkins & Rosalind Franklin

19. X-ray Crystallography
Physics approach to examining biological molecules.
A pure sample of the molecule is isolated.
X-rays bombard the sample and refract the rays in multiple directions.

20. Capillary tube holds sample; detector on the left

21. X-ray Crystallography

22. Rosalind Franklin’s X-rays
The photo indicated:

23. DNA Structure

24. What’s Left to Discover?
Hereditary molecule is DNA. DNA molecules are polynucleotides. DNA has a double-helix structure with alternating sugar-phosphate molecules. How are the bases arranged in the middle?

25. 1953 – James Watson & Francis Crick

26. 1953 – James Watson & Francis Crick
Inspired by alpha-helix model of proteins. Determined how A + T and G + C bonded together.

27. Base Pairing