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Discovering DNA

Discovering DNA. SBI4U0 Ms. Manning. 1869 – Friedrich Miescher. Used pus cells from infections (before antiseptics were widely used) to investigate chemical structure of hereditary material (thought to be protein at the time).

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Discovering DNA

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  1. Discovering DNA SBI4U0 Ms. Manning

  2. 1869 – Friedrich Miescher • Used pus cells from infections (before antiseptics were widely used) to investigate chemical structure of hereditary material (thought to be protein at the time)

  3. Found a large quantity of non-protein substance in nucleus that was slightly acidic and contained large amounts of phosphorus and nitrogen and called it NUCLEIN (due to location) – renamed DNA where chemical composition discovered • http://www.dnai.org/text/mediashowcase/index2.html?id=52

  4. 1930s – Joachim Hammerling • Used a large (5 cm) single-celled algae (Acetabularia) with 3 distinct parts (foot, containing nucleus, stalk and cap) • Cut off cap and new cap grew; cut off foot and NO new foot grew

  5. Grafted stalk of species A to foot of species B and new cap was an intermediate, cut off this cap and a second cap was that of species B • Conclusion = hereditary material in foot, likely nucleus

  6. 1920s • Determined that DNA has 3 main components: deoxyribose sugar, a phosphate group, and a nitrogen base • 4 types of nitrogenous bases – A, C, T and G; 2 of which are larger (A & G) and 2 of which are smaller (pyrimidines – C & T)

  7. 1920s to 1944 • Frederick Griffith (then Oswald Avery, Colin MacLeod (both Canadian!) and Maclyn McCarty) • While trying to develop a vaccine against pneumonia bacteria, Griffith discovered the process of transformation • Transformation = introduction of foreign DNA into a bacterium

  8. Later, Avery, MacLeod and McCarty isolated various components of the pneumonia bacteria and identified DNA as the transforming principle

  9. 1952 – Alfred Hershey and Martha Chase • Used viruses that infect bacteria (bacteriophages) because they are only composed of DNA and a protein coat

  10. This protein coat contains sulfur (which DNA does not) and DNA contains phosphorus (which protein does not) • They labelled the protein with a radioisotope of sulphur (S-35) and labelled the DNA with a radioisotope of phosphorus (P-32) and subjected each to separate bacterial cultures • Bacteria exposed to P-32 showed radioactivity, while those exposed to S-35 did not • viruses, which inject their hereditary material into bacteria for reproduction were injecting DNA • Conclusion = hereditary material was DNA

  11. 1949 – Erwin Chargaff • Chemically analyzed DNA to determine that the proportion of adenine (A) is equal to that of thyamine (T) and the proportion of (G) is equal to that of cytosine (C) • Also, total amount of purines equals total amount of pyrimidines

  12. 1953 – Rosalind Franklin & Maurice Wilkins • Each used x-ray diffraction analysis of DNA to determine its structure (crystallography)

  13. 1953 – James Watson & Francis Crick • Observed patterns of Wilkins’ and Franklin’s diffraction patterns (Franklin’s were key) which revealed a helix (corkscrew) shape about 2 nm (1 x 10-9 m) in diameter with a complete helical turn every 3.4 nm • Also used Chargaff’s results to build the double-helix structure of DNA

  14. Watson and Crick got the credit for the structure of DNA...Franklin got...nothing.

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