Transcript Discovering DNA

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
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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