Frederick Griffith (1928). Avery, McCarty & MacLeod (1944) Only DNA (not protein, lipid or carbohydrates) TRANSFORM bacteria Only DNA (not protein,

Frederick Griffith (1928)Frederick Griffith (1928)

Frederick Griffith (1928)Frederick Griffith (1928)

Frederick Griffith (1928)Frederick Griffith (1928)

Frederick Griffith (1928)Frederick Griffith (1928)

Avery, McCarty & MacLeod Avery, McCarty & MacLeod (1944)(1944)

• Only DNA (not protein, lipid or Only DNA (not protein, lipid or carbohydrates) TRANSFORM carbohydrates) TRANSFORM bacteriabacteria

• “ “Bacteria eaters”- Phage virus particlesBacteria eaters”- Phage virus particles (image from the 1990s)(image from the 1990s)

Hershey & Chase (1952)Hershey & Chase (1952)

Hershey & Chase (1952)Hershey & Chase (1952)• Viruses are made of protein and nucleic acid Viruses are made of protein and nucleic acid ONLYONLY• “ “Something” in the virus enters the cell and Something” in the virus enters the cell and gets incorporated into the genetic material gets incorporated into the genetic material (whatever that might be) of the bacteria(whatever that might be) of the bacteria• That “something” transforms bacteria to turn That “something” transforms bacteria to turn them into virus production factoriesthem into virus production factories

• Protein is full of a lot of the atom Sulfur; Protein is full of a lot of the atom Sulfur; nucleic acids have very littlenucleic acids have very little• DNA is full of the atom phosphorus; proteins DNA is full of the atom phosphorus; proteins have very littlehave very little

Hershey & Chase (1952)Hershey & Chase (1952)

• “ “Bacteria eaters”- Phage virus particlesBacteria eaters”- Phage virus particles (image from the 1990s)(image from the 1990s)

Hershey & Chase (1952)Hershey & Chase (1952)

DNA

• 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:Generally accepted:

• All living cells have DNA (plus many that All living cells have DNA (plus many that are not living)are not living)• Between species there is wide variation in Between species there is wide variation in the overall percentages of A, T, G & Cthe overall percentages of A, T, G & C• However, in all species A = T, C = GHowever, in all species A = T, C = G

• E.g.- Human A- 30.3%, T= 30.3 %, G= 19.5%, E.g.- Human A- 30.3%, T= 30.3 %, G= 19.5%, C= 19.9%C= 19.9%

• “ “Chargaff’s Rules”Chargaff’s Rules”

• Also, a cell before Also, a cell before meiosismeiosis has has twicetwice as as much DNA as a cell (sperm, egg) aftermuch DNA as a cell (sperm, egg) after

Erwin Chargaff (1947)Erwin Chargaff (1947)

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

• Image #51:Image #51:• HelixHelix• Repeating unitsRepeating units

“ “unit cell” of specificunit cell” of specific

parametersparameters• Phosphates onPhosphates on

the outside (basesthe outside (bases

inside)= “backbone”inside)= “backbone”• C2 formC2 form• Parallel width along lengthParallel width along length

Franklin (1951- 52)Franklin (1951- 52)

• Parallel width along lengthParallel width along length• Backbone must be parallelBackbone 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)Watson & Crick (1952)

• Many “Ah-Hahs”Many “Ah-Hahs”• A bonds to T (2 bonds), C bonds to G (3 A bonds to T (2 bonds), C bonds to G (3 bonds) and NOT bonds) and NOT vice versavice versa

• Consistent with whose previous research?Consistent with whose previous research?

Watson & Crick (1952)Watson & Crick (1952)

• 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…

conclusionsconclusions

Watson & Crick (1952)Watson & Crick (1952)“Nucleotide”

• All the data fit with Franklin’s, All the data fit with Franklin’s, Chargaff’s, etc… conclusionsChargaff’s, etc… conclusions

• And it looks good too!And it looks good too!

Watson & Crick (1952)Watson & Crick (1952)

• Part I- the model (what it looks Part I- the model (what it looks like)like)

• Part II- how it works (the “secret Part II- how it works (the “secret of life”)of life”)

• “ “Complimentarity” & replicationComplimentarity” & replication• “ “The Central Dogma” & information The Central Dogma” & information storagestorage

Watson & Crick (1952)Watson & Crick (1952)

• “ “The Central Dogma” & The Central Dogma” & information storageinformation storage

Watson & Crick (1952)Watson & Crick (1952)

DNA PROTEINRNA

Enzymes Cell Structure

Carbohydrates Nucleic AcidsLipids

• “ “Complimentarity” & replicationComplimentarity” & replication

• Their Model (paper #2)Their Model (paper #2)• “ “Semi-conservative” replication:Semi-conservative” replication:

Watson & Crick (1952)Watson & Crick (1952)