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History Of DNA Notes

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

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History Of DNA Notes

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  1. 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 • 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!

  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 and 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 you group: complete the timeline with the people and their major discoveries TIME LINE Pauling Hershey-Chase Levene Avery Franklin Watson-Crick Chargaff Griffiths

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