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Historical Approach Hershey, Chase (2018)

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Name: _____________________________Period: _____Date: ___________
The Experiments of Martha
Chase and Alfred Hershey
Introduction:
By 1952, scientists were reasonably certain that
either DNA or proteins composed genetic material.
Despite the experiments of Avery and his team, many
scientists still maintained that protein was a more likely
candidate. After all, a protein can be made of up to
twenty different amino acids; DNA only has four bases.
The work of Martha Chase and Alfred Hershey
helped settle this dispute. Chase and Hershey knew
what atoms DNA and protein contained although they
didn’t know the exact arrangement of the atoms. Further, the scientists knew how to attach
radioactive labels to atoms. (A radioactive label allows scientists to see where an atom went. For
example, if you give a plant water with a radioactively labeled oxygen, you’ll see that the oxygen
leaves the plant during light reactions, meaning O​2​ comes from H​2​O,not CO​2​). Below, you’re given the
benefit of current knowledge: you have the real chemical structures of select amino acids and DNA.
Chase and Hershey were also familiar with bacteriophages, viruses that infect bacteria. They
knew that viruses inserted genetic material into bacteria. Then, bacteria were forced to make more
viruses rather than make bacterial parts. In a sense, the bacteria
​ were ​transformed into
virus-producing factories! Armed with all this knowledge, the scientists designed an experiment to
show that DNA, not protein, is the genetic material. Your task is to propose what Hershey and Chase
did to come to this conclusion.
Summarize:
List three things Hershey and Chase knew (facts or skills) that enabled them to design their
experiment proving that DNA, not proteins, were the genetic material. You may also highlight these in
the passage instead of copying them below.
1. ____________________________________________________________________________
______________________________________________________________________________
2. ____________________________________________________________________________
______________________________________________________________________________
3. ____________________________________________________________________________
______________________________________________________________________________
Two common amino acids:
C= Carbon
H= Hydrogen
N= Nitrogen
O= Oxygen
P= phosphorus
S= Sulfur
DNA
What atoms do DNA and amino acids have in common?
1. ________
2.________
3. ________
4. ________
Which atom is ONLY found in DNA, not amino acids? _______________
Which atom is ONLY found in amino acids, not DNA?________________
Imagine you have a mix of protein and DNA in a container. You want to be able to tell apart the DNA
and protein. If you could only label ONE atom in each molecule(C, H, O, N, P, or S), which atom
would you label in each molecule?
In DNA molecules, I would label _________________________________________________.
In protein molecules, I would label _______________________________________________.
What is a bacteriophage?
Remember that Hershey and Chase used special viruses called bacteriophages
in their experiment. A bacteriophage is a virus that only attacks bacteria. Some
viruses, like HIV and the flu, attack human cells. Bacteriophages only attack
bacterial cells. Viruses attack other cells because they don’t have the capacity to
make their own ATP or DNA. Therefore, they insert a part of themselves into the
host (in this case the bacterial cell) and force the bacterial cell to make ATP and
more viral DNA.
Do you think viruses insert DNA or proteins into their host in order to force the host to produce more viruses?
Why? ___________________________________________________________________________________
______________________________________________________________________________________
_______________________________________________________________________________________
Hershey and Chase’s
Below is the setup for Hershey and Chase’s experiment. Draw the outcome of the experiment on the right.
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