1. DNA

2. Contained in chromosomes containing DNA and protein Nucleic acid is made up of nucleotides – Nitrogenous base – Deoxyribose sugar – Phosphate

3. Important Scientists in the Discovery of DNA Frederick Griffith Oswald Avery Alfred Hershey and Martha Chase Rosalind Franklin Francis Crick and James Watson

4. Mice and Transformation: Griffith’s Experiment

5. Fredrick Griffith 1928 Studied Streptococcus pneumoniae 2 strains – One pathogenic – One harmless

6. Frederick Griffith Hypothesized that when the live harmless bacteria was mixed with heat-killed disease causing, some “factor” was transferred from the heat-killed bacteria into the live bacteria – Transforming factor might be a gene

7. Fredrick Griffith Transformation: – Definition: change – Harmless bacteria became harmful when mixed with heat killed bacteria

8. Oswald Avery Repeated Griffith’s work (1944) Made extract from the heat-killed bacteria Tested three possible factors for transformation – DNA – RNA – Protein What was his conclusion? What factor allowed transformation to occur?

9. Alfred Hershey and Martha Chase 1952 The Hershey-Chase Experiment Studied viruses (bacteriophages) – Viruses: non-living particles smaller than a cell that can invade living cells

10. Fig. 16-3 Bacterial cell Phage head Tail sheath Tail fiber DNA 100 nm

11. Hershey and Chase Specifically looked at T2 T2 invades Escherichia coli bacteria Radioactive isotope of sulfur marked protein coat Radioactive isotope of phosphorus marked DNA What did they find?

12. Fig. 16-4-1 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P)

13. Fig. 16-4-2 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P) Empty protein shell Phage DNA

14. Fig. 16-4-3 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P) Empty protein shell Phage DNA Centrifuge Pellet Pellet (bacterial cells and contents) Radioactivity (phage protein) in liquid Radioactivity (phage DNA) in pellet

16. X-Ray Evidence Rosalind Franklin Used X-Ray crystallography to find out structure of DNA molecules Diffracts light to reveal image

17. X-Ray Evidence X near center shows DNA twists around center Angle of the X suggests two strands and the nitrogenous bases (hydrophobic) are near the center of the molecule Shows diameter of the double helix

18. The Double Helix James Watson and Francis Crick –Built three- dimensional models of DNA –Used Rosalind Franklin’s x-ray pictures of DNA to assist in the model –The Double Helix

19. The Double Helix Two complementary strands of DNA wrapped around each other Will have a uniform diameter Realized that hydrogen bonds held the two strands together (A with T; C with G) –Two hydrogen bonds between A and T –Three hydrogen bonds between C and G

20. Nitrogenous Bases Make up DNA molecules Two Types – Purines – two rings in the structure Adenine (A) Guanine (G) – Pyrimidines – one ring in the structure Cytosine (C) Thymine (T)

21. Chargaff’s Rule Chargaff studied percentages of nitrogenous bases (1950) Percentage of guanine and cytosine are almost equal Percentages of adenine and thymine are almost equal Chargaff’s Rule supports idea that Adenine (A) bonds to Thymine (T) and Cytosine (C) bonds to Guanine (G)

23. Fig. 16-5 Sugar–phosphate backbone 5 end Nitrogenous bases Thymine (T) Adenine (A) Cytosine (C) Guanine (G) DNA nucleotide Sugar (deoxyribose) 3 end Phosphate

24. p. 310 1-3 1.A fly has the following percentages of nucleotides in it’s DNA – 27.3% A – 27.6% T – 22.5% G – 22.5% C How do these numbers demonstrate Chargaff’s rule?

25. p. 310 1-3 2.How did Watson and Crick’s model explain the basis for Chargaff’s rule? 3.If transformation had not occurred in Griffith’s experiment, how would the results have differed? Explain.