1. The Race to Discover DNA’s Structure
1953
Compiled data from previous scientists to build a double-helical model of DNA
James Watson
Francis Crick

2. The Race to Discover DNA’s Structure

3. The Race to Discover DNA’s Structure
X-Ray diffraction image of DNA taken by Franklin in 1951
Maurice Wilkins
Rosalind Franklin

4. The Race to Discover DNA’s Structure was Over
DNA is made up of:
Four nucleotides: Adenine, Thymine, Guanine and Cytosine
These follow the rules of base-pairing:
Adenine bonds with Thymine
Guanine bonds with Cytosine
A sugar-phosphate backbone
DNA is arranged in an double-helix

5. DNA Two strands of DNA join together to form a double helix Base pair

6. DNA - double helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

7. The Race to Discover DNA’s Structure
Why do you think the bases match up this way?
1950
Chargaff’s Rule: Equal amounts of Adenine and Thymine, and equal amounts of Guanine and Cytosine
Purine + Purine = Too wide
Pyrimidine + Pyrimidine = Too Narrow
Erwin Chargaff
Purine + Pyrimidine = Perfect Fit from X-ray data

8. Bases Each DNA nucleotide has one of the following bases:
Thymine (T)
Cytosine (C)
One ring = Pyrimidine
Two rings= Purines
(Cut the pie small)
Adenine (A)
Guanine (G)

9. Functional Groups
Functional groups are attached to the carbon backbone of organic molecules. They determine the characteristics and chemical reactivity of molecules. Functional groups are far less stable than the carbon backbone and are likely to participate in chemical reactions.
Five examples are:
Hydroxyl
Carboxyl
Amino
Sulfhydryl
Phosphate