1. The Search and Discovery of Genetic Material
History Of DNA Notes
The Search and Discovery of
Genetic Material

2. Search For Genetic Material
Scientists prior to 1940s believed
proteins were the genetic material
Early discoveries
Levene (1919): discovered nucleic acids
Griffith (1928): discovers transformation
Avery (1944): discovers that DNA is the transforming agent.

3. Levene: 1919 Major Discovery:
Nucleotides contain: Sugar, phosphate and one of four nitrogen containing bases
Thought the bases were present in equal amounts (which is incorrect)
Levene, however, thought this was too simple to store genetic code and his work was largely discredited at the time.

4. Griffith’s Experiment: 1928
Discuss: Why do you think this occurs?
Major Discover:
There is a “transformation principle” that can transfer genetic information

5. Avery 1944
Used Griffith’s findings to further isolate what the “transforming principle” actually is
Isolated Cells of the infectious strain
Used enzymes to digest and remove:
Outer sugar coating
All proteins
All RNA
Left with only DNA: was still able to transform harmless strain.
Discuss: What do you think this discovery meant?
Major Discovery:
DNA carries the genetic information!

6. Discovering DNA’s Structure Key People and Places

7. Hershey-Chase Experiment: 1952
Major Discovery:
Confirm DNA carries information and protein.

8. Chargaff: 1949
Looking at possible differences in DNA among different species.
Major Discovery
“Chargaff’s Rule”:
amount of adenine (A) is usually similar to the amount of thymine (T)
amount of guanine (G) usually approximates the amount of cytosine (C).

9. Discuss: If the amount of: A is the same as T G is the same as C
What would you assume about
DNA structure?

10. The RACE begins In the 1940s/early 1950s, what did scientists know:
about genetic information?
What do you think they might be “racing” to figure out?
Answer? They knew the make up of DNA and of its genetic importance, but they now were racing to discover the STRUCTURE
Discuss this with your tablemates

11. The Contenders
Pauling Watson and Crick Franklin Wilkins

12. Rosalind Franklin: 1952
At this time, women were not highly regarded in the scientific world.
Franklin worked with many men, like Wilkins who saw her as an “assistant”
Major Discovery:
She used x-ray
crystallography to
take pictures of
DNA at different
angles
Discuss: why might this be important?

13. Pauling 1953 Linus Pauling was at the forefront of chemistry
very interested in protein
“wrote the book” on chemical bonds
Major Discovery: Knew the three components of nucleotides; Pauling believed the structure of DNA to be an alpha helix
INCORRECT

14. Watson and Crick:1953
Eccentric scientists who
worked together to put
information for multiple sources together:
Levene: nucleotides contain 3 parts
Griffith/Avery/Hershey-Chase: DNA carries genetic code
Chargaff: A + T and C + G
Franklin: helix structure
from x-ray photos
Discuss: Why might sharing data be important in science?

15. Watson and Crick’s Major Discovery

16. With your group: complete the timeline with the people and their major discoveries
Levene
Avery
Hershey- Chase
Pauling
1919
1928
1944
1949
1952
1953
Griffiths
Chargaff
Franklin
Watson- Crick