Avery+and+DNA

Oswald Avery (1877-1955)

Avery wanted to determine which molecule in the heat-killed bacteria was most important for transformation. He discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

In 1944, Avery led a group of scientists at the Rockefeller Institute conducted a series of tests where they made an extract, or juice, from heat-killed bacteria. They then carefully used enzymes to destroyed proteins, lipids, carbohydrates, and other molecules including the nucleic acid RNA. Transformation still occurred, so these molecules were not responsible for the transformation.

They repeated the experiment using enzymes that broke down DNA. When they destroyed the nucleic acid DNA in the extract, transformation did not occur. They concluded that DNA was the transforming factor. Therefore, genes are composed to DNA.

Avery's Experiment Simplified:

Oswald Avery and his co-workers built upon Griffith's work. He broke open the lethal bacteria and separated the bacterial components into its parts - lipids, polysaccharides, proteins and nucleic acids. Then he repeated Griffith's work but this time trying each component separately. He discovered that **only** the __nucleic acids__ transformed the harmless bacteria into lethal ones. He knew that there are two types of nucleic acids - DNA and RNA. Avery repeated his experiment but this time he treated the nucleic acids with an enzyme that destroys RNA while leaving the DNA unaffected. This "RNA-free" solution of nucleic acids was still able to transform harmless bacteria into lethal bacteria so Avery __proved__ that DNA is the genetic material! http://www.evolution-textbook.org/content/free/figures/02_EVOW_Art/15_EVOW_CH02.jpg