1. High School Biology Class
Chapter 12 - DNA
High School Biology Class

2. Virulent – disease-causing
Discovery of DNA
The discovery of deoxyribonucleic acid (DNA) is a relatively new development in the field of science formally beginning in 1900s.
Virulent – disease-causing

3. A) Frederick Griffith
In 1928, while working on a vaccine, Griffith made a fascinating discovery about DNA.
He found that when non-virulent bacteria and heat-killed virulent bacteria were mixed they created disease.

4. Griffith’s Experiment

5. B) Oswald Avery
In 1944, through a series of experiments Avery showed that DNA was responsible for transformations, like the bacteria in the mice.

6. Avery’s Experiments

7. C) Hershey & Chase
In 1952, Hershey & Chase proved DNA could be inherited.
They used radioactive samples of “P32” and “S35” to label parts of viruses.

8. Hershey & Chase’s Experiment

9. DNA’s Appearance
DNA is composed of many smaller units that we call nucleotides.
This is similar to the many small beads that make up a necklace.

10. Nucleotide Consists of 3 parts: 1) Deoxyribose Sugar 2) Phosphate
3) Nitrogen Base

11. Nitrogen Bases Can vary between four: 1) Adenine (A) 2) Guanine (G)
3) Cytosine (C)
4) Thymine (T)

12. Nitrogen Base Groups Adenine and Guanine consist of the Purines.
Cytosine and Thymine consist of Pyrimidines.

13. Structure of DNA

14. D) Erwin Chargaff
In 1949, Chargaff discovered that the amount of A always equaled T, and G always equaled C.
Chargaff’s Rules:
A pairs with T
G pairs with C

15. Complimentary Base Pairing

16. E) Rosalind Franklin
In 1952, Franklin used x-rays to find that a DNA molecule resembled a tightly coiled spring (helix).
* Franklin died at age 37 of cancer due to x-rays.

17. Franklin’s Experiment

18. F) Watson and Crick
In 1953, using the discoveries of the other scientists, Watson and Crick, completed the first model of DNA.
They also found that the bases were joined by hydrogen bonds.

19. Any Questions?
“Life is not easy for any of us. But what of that? We must have perseverance and above all confidence in ourselves. We must believe that we are gifted for something and that this thing must be attained.” --Marie Curie