1. Overview: Life’s Operating Instructions
DNA, the substance of heredity, is the most celebrated molecule of our time
Hereditary information is encoded in DNA and reproduced in “all” cells of the body
This DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits

2. Concept 16.1: DNA is the genetic material
Early in the 20th century, the identification of the molecules of inheritance loomed as a major challenge to biologists
The discovery of the genetic role of DNA began with research by Griffith in 1928
Griffith showed that bacteria contained a substance that could cause a genetic transformation
In 1944, Avery, McCarty and MacLeod announced that the transforming substance was DNA

3. More evidence for DNA as the genetic material came from studies of viruses that infect bacteria
Bacteriophages (or phages), are widely used in molecular genetics research
Simple systems that help to understand more complex ones: the “atom” of molecular biology

4. Bacteriophages were widely accepted as a model system
Consist of DNA and protein
Known to re-program genetics of infected cell

5. Alfred Hershey-Martha Chase “Blender” Experiment

6. In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA
Figure 16.1 How was the structure of DNA determined?

7. Watson and Crick relied on other scientists’ data
Rosalind Franklin produced some of the important X ray crystallographic images