1. The History of DNA
All life on earth uses a chemical called DNA to carry its genetic code or blueprint. In this lesson we be examining the structure of this unique molecule.
{Point out the alligator’s eyes in the first picture.} By the way, can you make out what this is?
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[The goal of this presentation is to introduce high school biology students to the chemical structure of DNA. It is meant to be presented in the classroom while accompanying the teacher’s lecture, under the control of the teacher.]

2. The History of DNA Gregor Mendel-1866
Determined “Unit characters” were the method of passing on traits for inheritance
Friedrich Meischer
Studied nuclei of pus cells obtained from discarded surgical bandages
Detected a phosphorus-containing substance that he named nuclein.

3. Frederick Griffith 1928 : Work with Bacteria
Found that DNA taken from a virulent (disease-causing) strain of bacteria (Streptococcus pneumoniae)
Transformed a non-virulent form of the bacterium into a virulent form.

4. Oswald Avery, Colin MacLeod, and Maclyn McCarty Continued the study of “Transformation” principle

5. Meischer
Mendel
Griffith
MacLeod
McCarty
Avery

6. Transformation Of Bacteria Two Strains Of Streptococcus
Capsule
Rough Strain
(Harmless)
Smooth Strain w/Capsule
(Virulent)

7. Transformation Of Bacteria -Griffith’s Experiment
Smooth (virulent)
OUCH!
Control
Rough
Control
Control
Experimental

8. The History of DNA Alfred Hershey and Martha Chase - 1952
radioactive isotope tracer experiment
bacterial virus (bacteriophage T2) infects a host cell ( bacterium Escherichia coli)
found that T2 virus DNA, not its protein coat, enters the host cell
genetic information for replication of the virus

9. Using S35 Did protein enter the bacteria?
T 2 grown in media containing S35 incorporate S35 into their proteins
Bacteria grown in normal non-radioactive media
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet.
T2 attach to bacteria and inject genetic material
The supernatant is radioactive, but the pellet is not.
Mix-O-Matic
Blending causes phage protein coat to fall off
Did protein enter the bacteria?
Is protein the genetic material?

10. Using P32 Did DNA enter the bacteria? Is DNA the genetic material?
T2 grown in P32 containing media incorporate P32 into their DNA
Bacteria grown in normal non-radioactive media
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
T2 attach to bacteria and inject genetic material
The pellet is radioactive, but the supernatant is not.
Mix-O-Matic
Blending causes phage protein coat to fall off
Did DNA enter the bacteria?
Is DNA the genetic material?

11. The History of DNA Structure
Erwin Chargaff “Chargaff’s rule”
four bases may occur in varying proportions in DNA of different organisms
# of A = # of T, w/ two hydrogen bonds
= # of G and C are present w/ 3 hydrogen bonds
Rosalind Franklin and Maurice Wilkins
X-ray diffraction study concluded DNA fibers have two strands.

12. The History of DNA Structure
James Watson and Francis Crick - University of Cambridge -1953
Worked on problem of making a DNA molecule model that was double stranded but also had the specific A - T and G - C base equivalencies
Solution-double helical structure for DNA.

13. Franklin
Chargaff
Wilkins

14. Watson and Crick