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Chapter 12 DNA & RNA

Chapter 12 DNA & RNA. DNA’s Structure. Purines: A & G - small name big molecule Pyrimadines: T & C - big name small molecule. Monomer = building block One Nucleotide is a monomer = nucleic acid + deoxyribose + phosphate (Nitrogenous Base). DNA’s Structure. 3’ has OH - hydroxide

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Chapter 12 DNA & RNA

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  1. Chapter 12 DNA & RNA

  2. DNA’s Structure Purines: A & G - small name big molecule Pyrimadines: T & C - big name small molecule Monomer = building block One Nucleotide is a monomer = nucleic acid + deoxyribose + phosphate (Nitrogenous Base)

  3. DNA’s Structure 3’ has OH - hydroxide 5’ has Phosphate Molecule • Directional Structure • Anti-parallel to each other • Always builds 5’ to 3’ • DNA Polymerase can only add to the 3’ end If DNA were synthesized in the 3' to 5' direction, the energy for the process would come from the 5' end of the growing strand rather than from free nucleotides. If the 5' nucleotide needed to be removed this triphosphate end would be lost, losing the energy source required to add a new nucleotide to the end.

  4. DNA’s Structure nm = 1 Billionth of a meter

  5. DNA Replication Semiconservative

  6. Chromosome Structure Key Terms: Histone = the protein Nucleosome = A cluster of histones Chromatin = DNA + Protein in an uncoiled form Chromosome = condensed chromatin Chromatid = each side of a chromosome Centromere = point of attachment of sister chromatids

  7. Evidence for DNA as Genetic Material • Griffith - 1928 • transformation • Avery, MacLeod, and McCarty - 1944 • Proves DNA is the transforming agent using enzymes • Hershey & Chase -1952 • Reproves Avery’s evidence using bacteriophage

  8. Time Line • 1866 Mendel publishes paper • 1900 Mendel’s paper rediscovered • 1902 chromosome theory of inheritance • 1905 the term “genetics” coined • 1950 base pairing discovered • 1953 Watson & Crick deduce the structure of DNA

  9. Griffith’s Transformation Experiments • Diplococcus pneumoniae • two strains: IIR & IIIS • two differences in genotype • R = rough, avirulent; S = smooth, virulent

  10. Griffith’s Transformation Experiments Live IIR Live IIIS

  11. Heat-killed IIIS Heat-killed IIIS + live IIR

  12. Heat-killed IIIS Live IIR

  13. Heat-killed IIIS Live IIR

  14. Explanations? • IIR cells mutated to S? • Serotype was changing • IIR were changing into IIIS • 2 mutations? • Only happened when IIR and dead IIIS mixed • Non-living component of IIIS cells changing genetics of IIR cells

  15. Avery, MacLeod and McCarty heat-killed IIIS + IIR removed polysaccharide coat heat-killed IIIS + IIR removed protein

  16. Avery, MacLeod andMcCarty heat-killed IIIS + IIR removed RNA heat-killed IIIS + IIR removed DNA

  17. Avery, MacLeod and McCarty • DNA is the transforming principle • DNA could change IIR bacteria into IIIS • Now know bacteria may pick up pieces of exogenous DNA and incorporate them into their own chromosomes = transformation

  18. Hershey and Chase • Studied bacteriophage • virus which attacks E. coli • Ran two side-by-side studies • labeled DNA of phage w/ 32P in one study • labeled protein of phage w/ 35S in second • In which study does radioactivity end up in E. coli?

  19. 32P labeled DNA 35S labeled protein

  20. Hershey and Chase • Mix phage and bacteria • Allow infection • Shear off what’s on outside - blender • Centrifuge • Look for radioactivity in pellet (bacteria)

  21. blender infection centrifuge Supernatant w/ protein coats E. coli w/ hot DNA

  22. blender infection centrifuge Supernatant w/ hot protein coats E. coli w/ DNA

  23. Summary Hershey & Chase

  24. Chargaff’s Rules 1947 Provided base pairing and hydrogen bonding

  25. Rosalind Franklin 1920-1958 (1951)

  26. Rosalind FranklinX-Ray Diffraction Provided idea of double helix

  27. Nobel Prize (1962) Made Model 1953 Frederick Wilkins James Watson Francis Crick

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