1. DNA
DNA was identified as the genetic material through a series of experiments

2. Molecular Genetics
Study of the chemistry of the materials of inheritance.
Structure of DNA
Contains information to construct the molecules needed for life (proteins).

3. Griffith and Transformation
1928 Frederick Griffith was researching pneumonia.

4. Griffith finds a ‘transforming principle.’
Griffith experimented with the bacteria that causes pneumonia.
Two types:
S = deadly (Sick)
R = harmless
TRANSFORMATION occurred
S changed R into harmful

5. Griffith’s Experiment
Heat killed disease causing bacteria
Disease causing bacteria
Harmless Bacteria
Heat Killed bacteria
No growth
Harmless bacteria
MOUSE CROAKS!

6. Transformation
Griffith mixes heat-killed disease causing bacteria with live harmless bacteria
The mice died
A factor from the heat killed bacteria had “transformed” *(CHANGED) the harmless bacteria into disease causing ones.

7. Griffith’s Experiment
Experiment Video

8. Avery and DNA Oswald Avery – 1944 Repeats Griffith’s experiment
Wants to know what caused the transformation?
Uses enzymes to break down or destroy parts of the pneumonia causing bacteria

9. Did transformation occur afterwards?
Avery and DNA
Parts of Bacteria
Did transformation occur afterwards?
Conclusion
Proteins
RNA
DNA

10. Avery's Experiment Enzyme to break down proteins
Transformation occurred-
Enzyme to break down RNA
Transformation occurred
Enzyme to break down DNA
NO TRANSFORMATION OCCURRED

11. Avery and DNA Conclusion: DNA caused transformation!
If is causes transformation then:
Could DNA be genetic material?

12. The Hershey-Chase Experiment
Alfred Hershey and Martha Chase -1952
Studied viruses
non-living particles smaller than a cell
can infect living organisms

13. 1952 Alfred Hershey and Martha Chase
Is genetic material made of DNA or Protein?
Used radioactive sulfur 35 and phosphorus 32
Bacteriophage

14. The Hershey-Chase Experiment
Bacteriophage – a virus that infects and kills bacteria (bacteria eater)
Composed of:
DNA or RNA core
protein coat

15. The Hershey-Chase Experiment
Phage infects bacterium
Bacteriophage with phosphorus-32 in DNA
Radioactivity inside bacterium
Phage infects bacterium
No radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat

16. The Hershey-Chase Experiment
Video

17. The Hershey-Chase Experiment
Conclusion: The genetic material is DNA

18. Francis Crick and James Watson 1953
Developed a 3-D model of DNA
Used information from other scientists
Two strands are wound around each other
Looks like:
Twisted ladder
Spiral staircase

19. Erwin Chargaff’s Rules 1950
Erwin Chargaff – American Biochemist
In any sample of DNA
Percentages of cytosine and guanine are almost equal
Percentages of thymine and adenine are almost equal
C=G and T=A
Percentages of Bases in Four Organisms
Sources of DNA A T G C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9

20. X-Ray Evidence Early 1950’s Rosalind Franklin used x-ray on DNA
X-shaped pattern suggests - two strands in the structure

21. Francis Crick and James Watson 1953
DNA is shaped as a double helix.
Two strands are wound around each other
Looks like:
Twisted ladder
Spiral staircase