1. DNA: Deoxyribose Nucleic Acid The Genetic Material
DNA’s History
Lecture #16
Ms. Day Honors Biology

2. DNA Deoxyribose nucleic acid  type of nucleic acid
What is the other type of nucleic acid?
RNA
DNA function
to hold genetic code
Genetic code = genetic instructions to make proteins
DNA is found in nucleus of eukaryotic cells
Found in nucleoid region in prokaryotes

3. The Short History of DNA and Genetics (Part 1)
From

4. Searching for Genetic Material
Freidrich Miescher(1868):
discovered DNA
Isolated something new from the nuclei of eukaryotic cells
Later called DNA!!!

5. Searching for Genetic Material
Fredrick Griffith (1928):
Studied effects of virulent (virus-causing) bacteria vs. nonvirulent bacteria injected into mice
He used transformation:
Inserted foreign DNA and changed protein/ trait
believed that the transforming agent was an inheritance molecule

6. Non-virulent vs. Virulent Bacteria
ROUGH: harmless
SMOOTH:
kill

7. NOT HARMFUL/BENIGN
BAD/HARMFUL

8. Griffith's Transformation Experiment
Used the Pneumococcus bacteria
a virulent S strain with a Smooth coat
kills mice
a non-virulent R Rough strain
does not kill mice.
Heat destroys (kills) living cells!!!
He heated smooth (harmful) cells
So cells were DEAD!
Then he mixed them with living Rough (benign) cells and injected into mice, BUT the mouse dies.
WHY?

9. Searching for Genetic Material

10. Searching for Genetic Material
Oswald Avery, Colin MacLeod, & Maclyn McCarty (1944):
Reported that “transforming agent” in Griffith's experiment was DNA
Also used the Pneumococcus bacteria and test tubes (NOT mice)

11. So…DNA is the transforming agent!!

12. Discovering the Structure of DNA
Edwin Chargaff (1950)
Discovered a 1:1 ratio of adenine to thymine and guanine to cytosine in DNA samples from a variety of organisms.

13. Relative Proportions (%) of Bases in DNA
Chargaff's Rule (Data)
Relative Proportions (%) of Bases in DNA
ORGANISM A T G C
Human
30.9
29.4
19.9
19.8
Chicken
28.8
29.2
20.5
21.5
Grasshopper
29.3
20.7 
Sea Urchin
32.8
32.1
17.7
17.3
Wheat
27.3
27.1
22.7
22.8
Yeast
31.3
32.9
18.7
17.1
E. coli
24.7
23.6
26.0
25.7

14. Discovering the Structure of DNA
Chargaff’s Rules
A = T
C = G

15. Discovering the structure of DNA
Maurice Wilkins (1952)
Photographed DNA using x-ray crystallography
Worked with another scientists named Rosalind Franklin
Awarded the 1962 Nobel Prize for Physiology or Medicine with Watson and Crick

17.  X-rays passing through a helix diffract at angles perpendicular to helix making an "X" pattern, which favors an equal diameter "helix".

18. Discovering the structure of DNA
Photo 51
Rosalind Franklin
(1952)
Obtained sharp X-ray diffraction photographs of DNA (Photo 51)
Watson and Crick used her data  revealed its helical shape
Watson and Crick went on to win Nobel Prize (1962) for their DNA model

19. She finally gets credit 
Rosalind Franklin University of Medicine and Science, located on Green Bay Road in
North Chicago, Illinois

20. Searching for Genetic Material
Alfred Hershey & Martha Chase (1952)
Confirmed DNA IS genetic material
Used bacteriophages (viruses)
HYPOTHESIZED DNA, not protein, is the hereditary material

21. Searching for Genetic Material
Hershey and Chase Experiment Animation

22. Searching for Genetic Material Hershey and Chase Experiment

23. Discovering the structure of DNA
James Watson & Francis Crick (1953)
Discovered double helix structure
Solved the three-dimensional structure of the DNA molecule