Transcript 3 DNA Experiments

DNA
Deoxyribonucleic Acid
I.
3 Experiments that proved
DNA is the genetic
material in cells.
1. Griffith (1928)
2. Avery (1944)
3. Hershey and Chase (1952)
A. Griffith (1928)
- discovers transformation
 Griffith
worked with:
- harmless Pneumococcus bacteria
- lethal Pneumococcus bacteria,
- and mice.
EXPERIMENT

1.) He injected mice with the

Mice LIVED
harmless bacteria.

2.) He injected mice with
lethal bacteria.

Mice DIED

3.) He killed the lethal
bacteria, and injected the
dead bacteria into the mice.

Mice LIVED

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.
(that is -DNA can store information!)
 Hershey
1.
2.
and Chase work with:
bacteriophage
radioactive tracers…
P32 for DNA and S35 for protein
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. 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. 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.
Practice Questions
1.
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