History Of DNA Notes
The Search and Discovery ofGenetic Material
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.
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.
Griffith’s Experiment: 1928
Discuss: Why do you think
this occurs?
Major Discover: There is a “transformation principle” that can transfer genetic information
Avery 1944
• Using Griffith’s to isolate what the “transforming principle”
• 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!
Discovering DNA’s Structure Key People and Places
Hershey-Chase Experiment: 1952• Major Discovery:– Confirm DNA carries
information and protein.
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).
If the amount of:A is the same as TG is the same as CWhat would you assume about DNA structure?
Discuss:
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
The Contenders
Pauling
Watson and Crick
Franklin and Wilkins
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?
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
Watson and Crick:1953• Eccentric scientists whoworked 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?
Watson and Crick’s Major Discovery
TIME LINE
1919 1928 1944 1949 1952 1952 1953 1953
Hershey-Chase
AveryLevene
Griffiths
FranklinChargaff
Pauling
Watson-Crick
With you group:
complete the timeline with the
people and their
major discoveries
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