The Search and Discovery of Genetic Material

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Presentation transcript:

The Search and Discovery of Genetic Material History Of DNA Notes The Search and Discovery of Genetic 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 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!

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).

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

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 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 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?

Watson and Crick’s Major Discovery

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