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

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

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

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

Alfred Hershey-Martha Chase “Blender” Experiment

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?

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