1. DNA & RNA
DNA

2. Griffith & Transformation
1928
Studying Natural Bacterial Pneumonia caused by:
Streptococcus pneumoniae
Smooth (pathogenic)
Rough (non-pathogenic)
S. pneumonia in sputum Notice capsule Gram Positive Diplococci

3. Streptococcus pneumonia
Type 3 VERY Mucoid
Optochin Disc

4. Griffith’s Experiments
Injected Mice
Smooth – Mice Died
Rough – Mice Didn’t Get Sick
Heat Killed Smooth
– Mice Didn’t Get Sick
Illness Not Caused By Poison

5. Mice Died Transformation
Mixed Heat Killed Smooth With Rough Live Bacteria.
Mice Died
Autopsy Revealed Lungs Full Of Smooth Strain of Bacteria
HOW?? Rough Bacteria Don’t Kill!

6. Griffiths Transformation

7. Transformation Heat Killed Smooth Bacteria
Still Contained The Information On How To Become Smooth
And Could Transmit That Info
And Transform Rough Bacteria To The Smooth (Pathogenic) Form

8. Avery & DNA 1944 Repeated Griffith’s Work
Then Did Experiments to Find Out What Was Transforming the Bacteria
By Treating The Extract From Heat Killed Smooth Bacteria To Destroy Specific Types Of Compounds

9. Treated Extract To Destroy Transformation Still Occurred
Avery & DNA
Treated Extract To Destroy
Proteins
Lipids
Carbohydrates
RNA
Transformation Still Occurred

10. Transformation Did NOT Occur
Avery & DNA
Then They Treated The Extract & Destroyed The DNA
Transformation Did NOT Occur
DNA Was The Transforming Factor

11. Avery & DNA
Key Concept Avery and other scientists discovered that DNA stores and transmits the genetic information from one generation of an organism to the next generation.

12. The Structure of DNA Chargaffs Rules
Discovered That Certain Nucleotides Were Always Present In The Same Percentages:
Adenine & Thymine
Guanine & Cytosine
% In Each Species Different
Nobody Knew Why

13. Hershey-Chase Experiment
1952
Studied Virus Particles, Especially Bacteriophages
Martha Chase & Alfred Hershey

14. Hershey-Chase Experiment
Bacteriophages
Composed of DNA or RNA
and a Protein Coat
Figured Whichever Part Entered The Bacteria – Carried The Genes
Used Radioactive Markers

15. Proteins Contain No Phosphorous
Radioactive Markers
Grew Viruses In Cultures Containing
Radioactive Phosphorus ( 32P )
and
Radioactive Sulfur ( 35S )
Proteins Contain No Phosphorous
DNA Contains No Sulfur

16. Nearly All The Bacteria Contained Therefore DNA Contained Genes
Radioactive Markers
Therefore:
If The Interior Of The Bacteria Contained:
( 32P ) Then DNA Contained Genes
( 35S ) Then Protein Contained Genes
Nearly All The Bacteria Contained
( 32P )
Therefore DNA Contained Genes

17. Hershey-Chase
Bacteriophage (virus that infects bacteria) Outer, Protein Coat Contains Sulfur – No Phosphorus
E. coli bacteria (infected by Bacteriophage) Bacteriophage DNA injected into the E. coli Bacteriophage DNA contains Phosphorous but NO Sulfur

18. Hershey-Chase

19. DNA, not Protein. Hershey - Chase Key Concept:
Hershey and Chase concluded that the genetic material of the bacteriophage was:
DNA, not Protein.

20. The Structure of DNA X-Ray Diffraction Rosalind Franklin Early 1950’s
Doesn’t Show Structure But Provides Clues
DNA Twisted In Coils
Two Strands
Nitrogenous Base In Center

21. Photo 51

22. The Double Helix Watson & Crick A Double Helix
Building 3 Dimensional Models
1953 Saw Franklins X-ray Work
Immediately Recognized What The Structure Had To Be:
A Double Helix

23. The Structure of DNA Scientists still didn’t know:
How information was carried between generations
How genes were structured
How genes were copied

24. The Structure of DNA DNA is a long Molecule of repeating nucleotides
Each nucleotide has 3 parts:
5 Carbon Sugar (Deoxyribose)
1 Phosphate Group
1 Nitrogenous Base

25. The Structure of DNA There are 4 Nitrogenous Bases in DNA
The 4 Bases are two types:
Purines which are Double Ring Molecules
Adenine
Guanine
Pyrimidines which are Single Ring Molecules
Cytosine
Thymine

26. Purines Pyrimidines

27. Watson & Crick
Key Concept: Watson & Crick’s Model of DNA was a Double Helix, in which Two (2) Strands were wound around each other.

28. The Structure of DNA
Phosphate/Deoxyribose Form Sides of the DNA Ladder
Nitrogenous Bases Forms Rungs of DNA Ladder

29. Explained Chargaff’s Rule
Watson & Crick
Discovered The Double Helix
Held Together By Hydrogen Bonds Between The Nitrogenous Bases
Base Pairing
A:T and G:C
Explained Chargaff’s Rule

30. Double Helix