The History of DNA Page 273-278 Page 279 Questions 1, 2, 4, 8

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

Nucleotide Pattern

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?

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

Griffith’s Experiment

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

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

Hammerling’s Experiment #1 no regrowth

Hammerling’s Experiment #2 What was his conclusion?

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

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

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?

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

Hershey & Chase Experiment

1950s – Maurice Wilkins & Rosalind Franklin

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.

Capillary tube holds sample; detector on the left

X-ray Crystallography

Rosalind Franklin’s X-rays The photo indicated:

DNA Structure

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?

1953 – James Watson & Francis Crick

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

Base Pairing