1. 11.2 Structure of DNA

2. Actual structure of DNA was a complete mystery
Big question: How did DNA hold genetic information and what did it look like?

3. 1. Deoxyribose Sugar - pentagonal ring
Inheritable genetic information is coded in the molecule called DNA (Deoxyribonucleic Acid).
DNA is a Polymer - built from monomers called Nucleotides
1. Deoxyribose Sugar - pentagonal ring
2. Phosphate Group - Phosphorus atom surrounded by four Oxygen atoms
3. Nitrogenous Base - a single or double ring of carbon and nitrogen atoms with functional groups

4. Purines - double ring nitrogenous bases
Adenine (A) & Guanine (G)
Pyrimidines - single ring nitrogenous bases
Thymine (T) & Cytosine (C)

5. Chargaff’s Rule: 1950 American Erwin Chargaff
Analyzed different organism’s DNA: variation in number and amount of A, T, G, C
Quantity of nucleotides in each organism he found A=T and G=C
Chargaff’s Rule:
Nucleotide number and concentration vary with each species.
A=T and G=C within a specie’s DNA

6. 1951 English Rosalind Franklin
Studied molecules using X ray Diffraction
Indicated a helix structure

7. 1953 American James Watson and English Francis Crick
Studying the structure of DNA
Rosalind wrote to Watson and when he saw the X-Ray evidence he also believed DNA to be a Helix

8. Complementary Base Pairing
Each nitrogenous base must pair (bond) with its complementary base
each fitting like a puzzle piece
Adenine (A) pairs to Thymine (T)
Guanine (G) pairs to Cytosine (C)

9. Two long chains of nitrogenous bases bond with with their base pair and form a ladder structure
"Backbone" are the phosphate and deoxyribose
"rung" of the ladder and the Nitrogenous bases