1. Frederick Griffith (1928)

5. Avery, McCarty & MacLeod (1944) Only DNA (not protein, lipid or carbohydrates) TRANSFORM bacteria Only DNA (not protein, lipid or carbohydrates) TRANSFORM bacteria

6. “Bacteria eaters”- Phage virus particles “Bacteria eaters”- Phage virus particles (image from the 1990s) (image from the 1990s) Hershey & Chase (1952)

7. Viruses are made of protein and nucleic acid ONLY Viruses are made of protein and nucleic acid ONLY “Something” in the virus enters the cell and gets incorporated into the genetic material (whatever that might be) of the bacteria “Something” in the virus enters the cell and gets incorporated into the genetic material (whatever that might be) of the bacteria That “something” transforms bacteria to turn them into virus production factories That “something” transforms bacteria to turn them into virus production factories Protein is full of a lot of the atom Sulfur; nucleic acids have very little Protein is full of a lot of the atom Sulfur; nucleic acids have very little DNA is full of the atom phosphorus; proteins have very little DNA is full of the atom phosphorus; proteins have very little

8. Hershey & Chase (1952)

9. “Bacteria eaters”- Phage virus particles “Bacteria eaters”- Phage virus particles (image from the 1990s) (image from the 1990s) Hershey & Chase (1952) DNA

10. Nucleic acids are made of four components: Nucleic acids are made of four components: Phosphate group: Phosphate group: Sugar (deoxyribose & ribose): Sugar (deoxyribose & ribose): Nitrogenous bases: Nitrogenous bases: Pyrimidines (1-ring): Pyrimidines (1-ring): Purines (2-ring): Purines (2-ring): Generally accepted:

11. All living cells have DNA (plus many that are not living) All living cells have DNA (plus many that are not living) Between species there is wide variation in the overall percentages of A, T, G & C Between species there is wide variation in the overall percentages of A, T, G & C However, in all species A = T, C = G However, in all species A = T, C = G E.g.- Human A- 30.3%, T= 30.3 %, G= 19.5%, C= 19.9% E.g.- Human A- 30.3%, T= 30.3 %, G= 19.5%, C= 19.9% “Chargaff’s Rules” “Chargaff’s Rules” Also, a cell before meiosis has twice as much DNA as a cell (sperm, egg) after Also, a cell before meiosis has twice as much DNA as a cell (sperm, egg) after Erwin Chargaff (1947)

12. “X-ray diffraction crystallography” “X-ray diffraction crystallography” Franklin (1951- 52)

13. Image #51: Image #51: Helix Helix Repeating units Repeating units “unit cell” of specific “unit cell” of specific parameters parameters Phosphates on Phosphates on the outside (bases the outside (bases inside)= “backbone” inside)= “backbone” C2 form C2 form Parallel width along length Parallel width along length Franklin (1951- 52)

14. Parallel width along length Parallel width along length Backbone must be parallel Backbone must be parallel Bases fill in the space between the “rungs” Bases fill in the space between the “rungs” But how? But how? Watson & Crick (1952)

15. Many “Ah-Hahs” Many “Ah-Hahs” A bonds to T (2 bonds), C bonds to G (3 bonds) and NOT vice versa A bonds to T (2 bonds), C bonds to G (3 bonds) and NOT vice versa Consistent with whose previous research? Consistent with whose previous research? Watson & Crick (1952)

16. Many “Ah-Hahs” Many “Ah-Hahs” C2 form? C2 form? All the data fit All the data fit with Franklin’s, with Franklin’s, Chargaff’s, etc… Chargaff’s, etc… conclusions conclusions Watson & Crick (1952) “Nucleotide”

17. All the data fit with Franklin’s, Chargaff’s, etc… conclusions All the data fit with Franklin’s, Chargaff’s, etc… conclusions And it looks good too! And it looks good too! Watson & Crick (1952)

18. Part I- the model (what it looks like) Part I- the model (what it looks like) Part II- how it works (the “secret of life”) Part II- how it works (the “secret of life”) “Complimentarity” & replication “Complimentarity” & replication “The Central Dogma” & information storage “The Central Dogma” & information storage Watson & Crick (1952)

19. “The Central Dogma” & information storage “The Central Dogma” & information storage Watson & Crick (1952) DNAPROTEINRNA Enzymes Cell Structure Carbohydrates Nucleic AcidsLipids

20. “Complimentarity” & replication “Complimentarity” & replication Their Model (paper #2) Their Model (paper #2) “Semi-conservative” replication: “Semi-conservative” replication: Watson & Crick (1952)