Group Reading…
Each group is going to be assigned a scientist/experiment to
read. Each group will need to have:
2 Readers
1 Scribe
(You decide in your group.)
1 Presenter
After reading about your scientists experiments answer
these questions about EACH!--Be ready to discuss and share with class!
1.What were the scientists trying to figure out? (what was
their question?)
2.Briefly describe the experiment they did to answer their
question.
3. Describe their results. (what they found out)
4. How/why are their results important to us today?
DNA
KWL
I. Testing for DNA
1928 -scientist Fredrick Griffith isolated a
harmful (smooth) bacteria and a rough (not
harmful) bacteria
*he was actually studying pneumonia bacteria
*When he grew the bacteria in the petri plates the
harmful one grew into little colonies with smooth
edges
*Harmless bacteria grew into little colonies with
rough edges
Smooth
Rough
– Griffith's Experiments
• Griffith set up four
individual
experiments.
• Experiment 1: Mice
were injected with the
disease-causing
strain of bacteria. The
mice developed
pneumonia and died.
• Experiment 2: Mice
were injected with
the harmless strain
of bacteria. These
mice didn’t get sick.
Harmless bacteria
(rough colonies)
Lives
• Experiment 3: Griffith
heated the diseasecausing bacteria. He
then injected the heatkilled bacteria into the
mice. The mice
survived.
Heat-killed diseasecausing bacteria (smooth
colonies)
Lives
• Experiment 4: Griffith mixed
his heat-killed, diseasecausing bacteria with live,
harmless bacteria and
injected the mixture into the
mice. The mice developed
pneumonia and died.
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia
1. “Dead” harmful bacteria and live safe
bacteria were combined and produced live
harmful bacteria
2. bacteria underwent “transformation” where
one bacteria picked up the DNA (genetic info)
from another bacteria
* At the time he knew the bacteria had
changed from harmless to harmful but he did
not know that DNA was to blame
Oswald Avery repeated Griffith’s work to determine
which molecule was most important for
“transformation”
1. Avery added enzymes to bacteria (breakdown
molecules); enzymes destroyed proteins, lipids,
carbohydrates, and RNA
a. the mouse still died because the DNA was still
being transferred!
*So if all the lipids, carbohydrates, proteins and RNA
were broken down what is still left? *DNA!!!
2. they discovered that DNA was responsible for
the transfer of genetic information
Hershey and Chase
• Bacterial viruses called bacteriophage were used to
show that DNA is genetic material.
• The phage consisted of a DNA molecule surrounded by
a protein coat.
• When the bacteriophage infect bacteria, they attach to
the surface and inject DNA into the cell. (the protein
coat stays outside)
• The first phages were covered in a radioactive label
(but the DNA was not), whenthe DNA was injected into
the cell, the radioactive coat stayed on the outside.
• The new viruses produced in the cell contained no
radioactivity.
• In the second part of experiment, they made a
phage that had radioactive labels on the DNA. Not
on the protein coat.
• When the phage infected the bacteria, the labeled
DNA entered the cell and was found in the infected
bacteria.
• This demonstrated that the DNA, not protein,
carries genetic information for a new generation of
viruses.
1.Which scientist did this
experiment?
2.What did the bacteria he
was using cause? (what
sickness)
3. What happened to the
harmless bacteria in the last
experiment that caused it to
kill the mouse?
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
*Answer these three questions on
a ¼ sheet of paper and turn in to
the basket!
Live disease-causing
bacteria
(smooth colonies)
Dies of pneumonia
• http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535
::535::/sites/dl/free/0072437316/120076/bio
21.swf::Hershey%20and%20Chase%20Experi
ment