1. Chapter 12.2 (Pg. 344-348): The Structure of DNA

2. Deoxyribonucleic Acid (DNA)
A nucleic acid made up of nucleotides joined into long chains by covalent bonds
Nucleotides have 3 parts:
Deoxyribose (5-carbon sugar)
Phosphate group
Nitrogenous base

3. Nitrogenous Bases Bases that contain nitrogen Four Types:
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Covalent bonds join nucleotides together in many different orders
Makes DNA backbone

5. Solving the Structure of DNA
Erwin Chargaff:
% of Adenine = % of Thymine
% of Guanine = % of Cytosine
Chargaff’s Rule: [A]=[T]; [G]=[C]
Rosalind Franklin
Shot X-Ray beams at DNA samples
Hypothesized a spiral structure
Watson and Crick
Used Franklin’s x-ray pictures to build a model of DNA

7. The Double-Helix Model
Looks like a twisted ladder or spiral staircase
Sides of the ladder made up of phosphate and sugar
Each side, or strand, of DNA runs antiparallel (opposite directions)

8. Base-Pairing Rule Bases held together by hydrogen bonds
A binds with T
G binds with C
Creates perfect fit in the center of the helix
Double-helix model explains Chargaff’s rule of base pairing (A=T; G=C)

9. Relationship Between DNA and Genes
The combination of base letters determines your traits
Example: CATGAT = Red Hair
AGTCA = Blue Eyes
DNA bases are like letters in a word
Multiple words make endless combinations of sentences