DNA: The Building Block of Life …the basis for inheritance and evolutionary theory!

Where do we find DNA? All living things contain DNA DNA is the basis of heredity (inheritance) Encodes the “blueprints” that direct all functions within cells and organisms

The Search for Genetic Material: 1. Griffith (1928) Worked with two kinds of bacteria; found bacteria could incorporate external genetic material in a process now called transformation

The Search for Genetic Material: 2. Avery (1944) Continued the work of Griffith & proposed that DNA was the molecule that transformed the bacteria

The Search for Genetic Material: 3. Hershey & Chase (1952) Proved that viruses contain DNA that can be injected into bacterial cells AND can replicate within those cells! Radioactive phosphorus “labeled” the DNA

The Search for Genetic Material: 4. Chargaff (1947) Reported ratio of nitrogenous bases was species specific Determined # of adenines = # thymines and # of guanines = # cytosines… this is known as Chargaff’s Rule! A - T C - G Complementary base pairs

The Guys who put it all together… 5.Watson & Crick Determined 3D shape of DNA Idea of the “double helix” based on 1 purine pairing with 1 pyrimidine (nitrogenous bases) and a sugar-phosphate backbone

The unsung hero of this story… Rosalind Franklin: X-ray crystallographer- her images are what Watson & Crick used in their work

Semi-Conservative Model Each side of DNA helix complementary to the other When replicating, 2 daughter DNA strands have 1 old strand from parent DNA and 1 new strand