Deoxyribonucleic Acid DNA Deoxyribonucleic Acid
3 Experiments that proved DNA is the genetic material in cells. 1. Griffith (1928) 2. Avery (1944) 3. Hershey and Chase (1952)
Griffith (1928) - discovers transformation Griffith worked with: - harmless Pneumococcus bacteria - lethal Pneumococcus bacteria, - and mice.
EXPERIMENT Mice LIVED Mice DIED 1.) He injected mice with the harmless bacteria. 2.) He injected mice with lethal bacteria. 3.) He killed the lethal bacteria, and injected the dead bacteria into the mice.
He injects harmless bacteria and dead lethal bacteria into the mice Mice DIED!!! The live harmless bacteria had been transformed (changed) into lethal bacteria by the dead lethal bacteria! He called this transformation.
The next big question? What kind of chemical caused the cells to change? Was it DNA or protein?
B. Avery (1944) - discovers protein is NOT the transforming agent (but he doesn’t prove DNA is – drats!) His experiment was also with harmless Pneumococcus bacteria lethal Pneumococcus bacteria and mice
What Avery did to get ready: He chopped up heat-killed lethal bacteria. He took the DNA out of some dead lethal bacteria and protein out of the dead lethal bacteria What do you think Avery is going to do next?
1.) He injected mice with harmless bacteria + just the protein from dead lethal 2.) He injected mice with harmless bacteria + just the DNA from dead lethal bacteria MICE LIVED MICE DIED!
CONCLUSION: Only the harmless bacteria + DNA from dead lethal bacteria killed the mice. He has proven that protein is NOT the transforming agent!
C. HERSHEY and CHASE (1952) - prove that DNA is the transforming agent C. HERSHEY and CHASE (1952) - prove that DNA is the transforming agent. (that is -DNA can store information!) Hershey and Chase work with: bacteriophage radioactive tracers… P32 for DNA and S35 for protein
Bacteriophage = a virus that infects bacteria Bacteriophage = a virus that infects bacteria. (Bet you didn’t know that bacteria can get sick.) Made of DNA or RNA surrounded by a protein capsid. Radioactive tracers can be used to follow molecules taking X-ray pictures. Protein has sulfur in it. The phage protein was labeled with S35 DNA has phosphorus in it. The phage DNA was labeled with P32
What Hershey and Chase did: They infected bacteria with viruses made with P32 in the DNA and S35 in the protein. After the infection, the viruses are separated from the bacteria. RESULT: Infected bacteria contain P32 and not S35 CONCLUSION DNA got into the transformed bacteria! DNA IS THE GENETIC MATERIAL!
In your notebook…. 1. Record the following about Griffith’s experiment A. Question or problem: B. Hypothesis (If…then…) C. Independent variable: D. Dependent variable: E. Control variables: Conclusion:
Get out your notebook, please. 2 Get out your notebook, please. 2. Record the following about Avery’s experiment: A. Question or problem: B. Hypothesis (If…then…) C. Independent variable: D. Dependent variable: E. Control variables: Conclusion:
Get out your notebook, please. 3 Get out your notebook, please. 3. Record the following about about the Hershey and Chase experiment A. Question or problem: B. Hypothesis (If…then…) C. Independent variable: D. Dependent variable: Conclusion:
DNA gel electrophoresis: a way to identify someone’s DNA.
Who discovered the structure of DNA? Practice Questions Who discovered the structure of DNA? a) Hershey and Chase b) Avery c) Griffith d) Watson and Crick
2. In which of the following experiments was transformation first discovered? a) Hershey and Chase b) Avery c) Griffith d) Watson and Crick
3. Which of the following statements most accurately describes a bacteriophage (virus)? A) it is a bacteria with a protein coat and a DNA core B) it is an isotope that can be seen using X-rays C) it is a virus that infects bacteria