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DNA Scientists

DNA Scientists. Ch. 12-1 p. 286. Griffith and DNA. Griffith and Transformation Look at the results How did this happen ? Transformation – one strain had been changed into another strain Must be a gene that was transferred and caused the transformation. Avery and DNA.

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DNA Scientists

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  1. DNA Scientists Ch. 12-1 p. 286

  2. Griffith and DNA • Griffith and Transformation • Look at the results • How did this happen? • Transformation – one strain had been changed into another strain • Must be a gene that was transferred and caused the transformation

  3. Avery and DNA • Repeated Griffith’s work to figure out which molecule was important for transformation • What does this mean? • DNA stores and transmits the genetic information

  4. Hershey-Chase Experiment • Wanted to find out whether genes were made of DNA or proteins • Bacteriophages – virus that infects bacteria; “bacteria-eater” • Experiment • Took 2 viruses • Marked 1 for DNA, marked the other for protein • mixed them with bacteria • What do you think happened?

  5. Hershey-Chase Experiment • Only the DNA marker showed up, not the protein marker • What does this mean? • It means that genetic material is made of DNA, not protein

  6. Components and Structure of DNA • Gene requirements • Carry information from one generation to the next • Determine heritable characteristics of organisms • Had to be easily copied

  7. Components and Structure of DNA • DNA is made of nucleotides • Nucleotides have 3 parts • Sugar – deoxyribose • Phosphate group • Base – nitrogen containing • Purines – two rings • Adenine (A) • Guanine (G) • Pyrmidines – one ring • Thymine (T) • Cytosine (C)

  8. Components and Structure of DNA • DNA has a backbone • Sugar – deoxyribose • phosphate • Bases can be put in any order, like the letters of the alphabet • Each order means something different

  9. Chargaff’s Rules • The number of G is almost exactly equal to the number of C • The number of A is almost exactly equal to the number of T • This rule applied to all living organisms – flies, dogs, humans, trees

  10. X-ray Evidence and the Helix • Rosalind Franklin • Aimed X-rays at DNA samples and got an X-shaped picture • She didn’t quite know what it meant • Watson and Crick • Were trying to shape DNA • Saw Franklin’s picture and knew • IT WAS A DOUBLE HELIX

  11. Double Helix • Looks like a twisted ladder • What holds the two pieces together? • hydrogen bonds • Can only form between base pairs • A-T and C-G

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