Discovering DNA Three famous experiments that paved the way to the human genome project.

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Presentation transcript:

Discovering DNA Three famous experiments that paved the way to the human genome project

Griffith and Transformation Two kinds of bacteria cause pneumonia in mice: smooth and rough Smooth bacteria kill the mice; rough do not Killed smooth bacteria do not kill mice Mixtures of smooth killed bacteria and rough bacteria should not have killed mice But it did Isolation of bacteria from the dead mice showed only smooth bacteria. What happened?

Griffith and Transformation Conclusion: Some molecule or group of molecules had changed harmless rough bacteria into deadly smooth bacteria Griffith called this process transformation and the molecule “the transformation factor”

Avery and the conclusion Test which molecules were the transformation factor Remember your macromolecules Heat killed bacteria were treated with enzymes that destroy proteins, lipids, carbohydrates and nucleic acids No treatment effected the transformation factor except one…………………..

Survey says…… The enzyme that destroyed DNA stopped the action of the transformation factor Avery concluded that the transformation factor was DNA The information to transform bacteria (the gene) was DNA

Hershey and Chase Bacteriophage experiments Do you know what a Bacteriophage is? Virus contains DNA and protein Which of these molecules is the genetic material. It should be what the virus infects the cell with, they said.

Hershey and Chase Sidebar: do you remember what an isotope is? –Atoms with the same number of protons (i.e. the same element) but different numbers of neutrons –Some are stable, some are not –The ones that are not are radioactive

Hershey and Chase Isotopes become part of molecules no matter if they are stable or unstable Labeling DNA –Use P Labeling protein –Use S Bacteria were grown in P32 or S35 and infected with phage The phage were collected and used to infect bacteria

Hershey and Chase Only one of the samples of phage made the bacteria radioactive The phage labeled with P32 Conclusion: the genetic material of the Bacteriophage is DNA not protein

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