1. DNA’s Discovery and Structure

2. Scientists that determined DNA’s Structure and Importance
1866 Gregor Mendel – demonstrated that parents pass traits to offspring-thought traits contained in a molecule
1869 Friedrich Meisher – Isolated DNA from cell nucleus – named it nucleic acid
1889 R.A. Altman-determined the chemical composition of DNA
Meischer- Johannes Friedrich Meischer - Isolated DNA from leukocytes (WBC’s) from pus in bandages. Cells were thought to be composed almost entirely of protein at the time. He named the substance nuclein and proved it was not a protein. He demonstrated it was found in a large number of cell types. Also proposed that it might be the molecule of heredity. DNA was acidic, there were also basic proteins in the mix thus the big question

3. Scientists that Determined DNA’s Structure and Importance
1919 Phoebus Levene – Determined the structure of a DNA nucleotide
– first to propose that DNA was a polymer made of
nucleotides
P = Phosphate S= 5C sugar B= Nitrogen base
Russian – Also identified Deoxyribose as the sugar in DNA and ribose in RNA- Polymer idea was the polynucleotide model he believed that DNA was a repeating sequence of nucleotides GCTA as such he also recognized that each nucleotide contained only one of each base.

4. Scientists that Determined DNA’s Structure and Importance
1928 Frederick Griffith – bacterial transformation – traits passed by a chemical
“transforming principle”
Griffith – English microbiologist was studying the cause of pneumonia. Studied two strains one rough-less virulent and one smooth
more virulent. He was able to culture live smooth from the hearts of dead mice

5. Scientists that Determined DNA’s Structure and Importance
1944 Oswald Avery – DNA =
key to transformation
- Avery and his partners
conducted experiments which
proved that DNA was Griffith’s
“transforming principle”
Oswald Avery, Maclyn McCarty, and Colin MacCleod – Their published paper was very carefully stated and they did not overtly claim that they had proven that DNA was the transforming principle. To anyone who read the paper without a bias, it was inescapable but
To people who had a dog in the hunt, they hadn’t eliminated protein conclusively- criticism centered on the possibility that protein remained after purification

6. Scientists that Determined DNA’s Structure and Importance
1949 Erwin Chargaff – base-pairing rules
%Adenine=%Thymine %Guanine=%Cytosine
1952 Alfred Hershey & Martha Chase
Radioactive labeled Bacteriophage transformation experiment-settled DNA-protein debate

7. Hershey & Chase

8. Important Scientists in the “Race for the Double Helix”
1952Maurice Wilkins & Rosalind Franklin
X-ray diffraction- “photographs” of DNA
DNA must be a some type of spiral (helix)
DNA’s diameter is constant and stable

9. Important Scientists in the “Race for the Double Helix”
1953 James Watson & Francis Crick
Created the first accurate 3-D model of DNA
Won the Nobel Prize with Wilkins

10. DNA is composed of nucleotides
DNA’s Structure
DNA is composed of nucleotides
DNA contains four nitrogen bases:
adenine(A) cytosine(C) guanine(G) thymine (T)
A & G are purines C & T are pyrimidines

11. DNA’s Structure DNA is a double helix
-2 strands of DNA nucleotides joined to form a
“twisted ladder”
-the strands are held by hydrogen bonds between the nitrogen bases

12. Chargaff’s Rule A == T C == G T == A G == C
The nitrogen bases form the “steps” on the DNA ladder by complementary pairing
A == T
C == G
T == A
G == C
A == T A always pairs with T
T == A C always pairs with G
Sugar-phosphate backbone

13. Central Dogma of Molecular Biology
1958 Francis Crick proposed:
DNA codes for the production of RNA
RNA codes for the production of protein
Protein does not code for the production of protein DNA or RNA
“Once information has passed into protein it cannot get back out again”

14. Vocabulary:
Mendel, Meischer, Altman, Levene, Griffith, Avery, Chargaff, Hershey & Chase, Franklin & Wilkins, Watson & Crick, nucleotide, deoxyribose, deoxyribonucleic acid complementary base pairing, double helix, Central Dogma of Molecular Biology