Biology 8.1 Identifying DNA as the Genetic Material PDF

**8.1 Identifying DNA as the Genetic Material** **Griffith finds a "transforming principle."** S (smooth) - lethal R (rough) - non-lethal **Avery identified DNA as the transforming principle.** They combined living R bacteria with an extract made from S bacteria. They next develop a process to...

**8.1 Identifying DNA as the Genetic Material** **Griffith finds a "transforming principle."** S (smooth) - lethal R (rough) - non-lethal **Avery identified DNA as the transforming principle.** They combined living R bacteria with an extract made from S bacteria. They next develop a process to purify their extract. Then they performed a series of tests to find out if the transforming material was DNA or protein. - - - Enzyme that destroys protein The extract still transformed the R bacteria to the S form. ------------------------------ ------------------------------------------------------------- Enzyme that destroys RNA The extract still transformed the R bacteria to the S form. Enzyme that destroys DNA There was no transformation. **Hershey and Chase confirmed that DNA was the genetic material.** Hershey and Chase were studying viruses that infect bacteria (bacteriophage). They take over a bacterium's genetic machinery and direct it to make more viruses. Protein - contains sulfur, but very little phosphorus. DNA - contains phosphorus, but no sulfur Experiment 1: Bacteria were infected with phages that had radioactive sulfur atoms around their protein molecules. They separated the bacteria from the parts of the phages that remained outside the bacteria. When they examined the bacteria, they found no radioactivity. Experiment 2: Next, they repeated the procedure with phages that had DNA tagged with radioactive phosphorus. This time, radioactivity was clearly present inside the bacteria. From their results, Hershey and Chase concluded that the phages' DNA had entered the bacteria, but the protein had not. Their findings finally convinced scientists that the genetic material is DNA and not protein.