8.1 Identifying DNA as the Genetic Material Set up Cornell Notes on pg. 3 Topic: 8.1 Identifying DNA as the Genetic Material Essential Question: Summarize: Why was bacteriophage an excellent choice for research to determine whether genes are made of DNA or proteins? 8.1 Identifying DNA as the Genetic Material 2.1 Atoms, Ions, and Molecules Summarize: Why was bacteriophage an excellent choice for research to determine whether genes are made of DNA or proteins? Key Concept:DNA was identified as the genetic material through a series of experiments
KEY CONCEPT DNA was identified as the genetic material through a series of experiments.
Frederick Griffith (1928) Microbiologist studying the bacterium that causes pneumonia to create a vaccine He studied two types S- smooth- Pneumonia + death R- rough- Pneumonia + recovery
Hypothesize what would Griffith expect to find if he combined the live S bacteria with live R bacteria? +
Griffith’s Experiments Griffith injected the two types of bacteria into mice What should Griffith expect to find when he injects the S (encapsulated) bacteria into the mice? What about the R (non-encapsulated) bacteria?
Hypothesize why only the S (encapsulated) strain would be deadly. The capsule protects the bacteria from the immune system!
Hypothesize what happened when Griffith heat-killed the S bacteria and injected it into the mice. When Griffith heat-killed the S bacteria and injected it into the mice, they were unaffected (healthy and alive).
Hypothesize what Griffith expect to find if he combined the dead S bacteria with live R bacteria?
When Griffith injected mice with a combination of heat-killed S bacteria and R bacteria the mouse died!!! What do you think he found when he took a blood test of the dead mouse?
When he did a blood test on the dead mouse he found live S bacteria in the dead mice!
Table Talk Hypothesize with your table about what happened when the heat-killed S bacteria was combined with the R bacteria. Remember: Live R= live mouse Heat-killed S= live mouse Live R + Heat-killed S= dead mouse
A “transforming material” passed from dead S bacteria to live R bacteria, making them deadly.
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.
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.
Avery’s Experiments (DEMO) Broke down the Heat-killed S bacteria into its components Carbohydrates Lipids Proteins DNA RNA He then added Live R bacteria What should we expect to happen to each animal? Rabbit 1: Carbs T-Rex 2: Lipids Rabbit 3: Proteins Snail 4: DNA Elephant 5: RNA
Avery’s Experiments Cont’ (DEMO #2) Even though this was good evidence that DNA was the genetic material, more evidence was needed. This time scientists decided to add enzymes that destroyed specific components of the Heat-killed S bacteria What should we expect to happen to each animal? Rabbit 1: Carb destroying enzyme T-Rex 2: Lipid destroying enzyme Rabbit 3: Protein destroying enzyme Snail 4: DNA destroying enzyme Elephant 5: RNA destroying enzyme
Transformation ONLY stopped when an enzyme was added that destroyed DNA!!!
He thought DNA was the transforming principle, but more proof was needed…
Hershey and Chase studied viruses that infect bacteria, or bacteriophages. (1952)
This confirmed that DNA was 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!
Biologix DNA Video