Transcript Document
8.1 Identifying DNA as the Genetic Material SPONGE 1 Open your biology book to page 225, and write a summary explaining what makes this mouse glow. 8.1 Identifying DNA as the Genetic Material • The mouse’s green glow comes from the green fluorescent protein GFP. Scientists put a gene from a glowing jellyfish into a virus that was allowed to infect a mouse egg. The jellyfish gene became part of the mouse’s genes. As a result the mouse cells produce the same protein. 8.1 Identifying DNA as the Genetic Material KEY CONCEPT DNA was identified as the genetic material through a series of experiments. 8.1 Identifying DNA as the Genetic Material • Frederick Griffith (1928) – Microbiologist studying the bacterium that causes pneumonia » He studied two types o S- smooth o R- rough 8.1 Identifying DNA as the Genetic Material •Griffith injected the two types of bacteria into mice •only the S type killed the mice. 8.1 Identifying DNA as the Genetic Material What would Griffith expect to find if he combined the live S bacteria with live R bacteria? 8.1 Identifying DNA as the Genetic Material •When Griffith heat-killed the S bacteria and injected it into the mice, they were unaffected. 8.1 Identifying DNA as the Genetic Material What would Griffith expect to find if he combined the dead S bacteria with live R bacteria? 8.1 Identifying DNA as the Genetic Material •When Griffith injected mice with a combination of heatkilled S bacteria and R bacteria the mouse died!!! 8.1 Identifying DNA as the Genetic Material •When he did a blood test on the dead mouse he found live S bacteria in the dead mice! Hypothesize with your table about what happened when the heat-killed S bacteria was combined with the R bacteria. 8.1 Identifying DNA as the Genetic Material • A “transforming material” passed from dead S bacteria to live R bacteria, making them deadly. 8.1 Identifying DNA as the Genetic Material • Oswald Avery, a biologist, spent 10 years trying to figure out what Griffith had discovered (1944) • He combined R bacteria with an extract made from S bacteria and observed R bacteria turning into S bacteria. 8.2 Structure of DNA SPONGE 2 1. What happened when Griffith injected the S bacteria into the mice? 2. The R bacteria? 3. The heat-killed S bacteria? 4. What did the mixture of dead S bacteria and live R bacteria do to the mice? 5. Why did this happen? (#4) What was the transforming material? 8.2 Structure of DNA 1. What happened when Griffith injected the S bacteria into the mice? They died. 2. The R bacteria? They lived. 3. The heat-killed S bacteria? They lived. 4. What did the mixture of dead S bacteria and live R bacteria do to the mice? Killed them. 5. Why did this happen? The live-S bacteria was found in the dead mouse. DNA from the dead S bacteria was transferred into the harmless R bacteria, making it deadly. 8.1 Identifying DNA as the Genetic Material • Wanted to know if it was DNA or protein that transformed harmless R bacteria into deadly S bacteria – tests showed DNA was present when proteins were not. – chemical makeup matched that of DNA. 8.1 Identifying DNA as the Genetic Material – When enzymes that were known to break down proteins were added, R bacteria still transformed into S bacteria. – Transformation ONLY stopped when an enzyme was added that destroyed DNA 8.1 Identifying DNA as the Genetic Material • He thought DNA was the transforming principle. 8.1 Identifying DNA as the Genetic Material • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. (1952) – They confirmed that DNA was the genetic material 8.1 Identifying DNA as the Genetic Material –They tagged viral proteins with radioactive sulfur • They tagged viral DNA with radioactive phosphorus • Tagged DNA was found inside the bacteria; tagged proteins were not. This confirmed that DNA was the genetic material!