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 O2 comes from H2O,not CO2). 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.