1. + The Hunt for DNA Chapter 13

2. + 1928 British scientist – Frederick Griffith - Griffith isolated 2 types of pneumonia bacteria: S strain – - R strain – -

3. + Griffith’s Experiment

4. + WHAT HAPPENED??? Somehow the heat killed bacteria passed the ability to cause disease to the harmless strain of bacteria -

5. + Oswald Avery 1944 Canadian scientist Oswald Avery - EXPERIMENT -. They treated the mixture with enzymes that destroyed proteins, lipids, carbohydrates, and nucleic acids RESULTS Transformation still occurred -

6. + Hershey and Chase - They wanted to know what which part of the virus – the protein coat or the DNA core – entered the bacterial cell EXPERIMENT Grew cultures of viruses in radioactive isotopes DNA was marked with phosphorus Protein was marked with sulfur RESULTS -

7. + Hershey and Chase Confirms DNA’s Function

8. + DNA must do 3 things… 1. - 2. - 3. - Therefore… the structure of DNA must allow for these functions. STRUCTURE = FUNCTION

9. + DNA - 3 basic parts - -) - Adenine Guanine Cytosine Thymine

10. + Chargaff’s Rule - The amount of adenine and guanine differs among species A = T G = C

11. + Rosalind Franklin - She stretched DNA fibers and aimed a powerful X-ray beam that formed the scattered pattern below. What does the picture suggest? Twisted structure -

12. + Watson and Crick 1953 - Using Chargaff’s rule and Franklin’s picture, Watson and Crick built a structural model of DNA -

13. + DNA STRUCTURE Features Sugar phosphate backbone Rungs of ladder are made by complementary base paring. -

14. + hydrogen bonds At first Watson and Crick could not explain what held the two strands together, until they discovered hydrogen bonds could form between nitrogenous bases. -

15. + Patterns of Base Pairing How do just two kinds of base pairings allow for such diversity? -

16. + “Variations in its base sequence from one individual or one species to the next is the basis of life’s diversity.”

17. + Complementary Strands If a strand of DNA had the following base pairs, what would be the complementary strand? AATCGCTACG