The History of Science: DNA
Name: ______Period: ______
The History of Science: DNA
Instructions: Please fill out any blank cells in the tables below. Most sections also require that you summarize the conclusions of each set of experiments.
Fred Griffith’s Mice/Pneumococcus Experiments
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Background information: Griffith was investigating two strains of Pneumococcus bacteria: the S (smooth) strain and the R (rough) strain. The S strain has a sugar coating that helps protect the cell against an organism’s immune system. The R strain does not have this coat. The S strain causes pneumonia in mice; the R strain does not.
Griffith’s experiment involved the denaturation of proteins. When proteins are heated up to a particular temperature, they denature (lose their 3-dimensional structure). When a protein denatures, it can no longer function properly.
Experimental Group / Experimental Conditions / Results (Did the mice live, die?)1 / Mice injected with live S strain bacteria
2 / Mice injected with live R strain bacteria
3 / Mice injected with heat-killed S strain bacteria
4 / Mice injected with heat-killed S strain bacteria + live R strain bacteria
What was learned from this experiment?
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Oswald Avery, Colin MacLeod andMaclyn McCarty’s test tube assay
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Background information: Avery et al. wanted to identify of the “transforming factor” from Griffith’s experiment that caused non-virulent R strain Pneumococcus to become deadly. First they lysed (broke open) heat-killed S bacteria. They knew that an S strain lysate contained four main components: a sugar coating, protein, and two types of nucleic acids (DNA and RNA).
Experiment Number / Experimental conditions / Lysate components present / Result(Did transformation occur?) / Conclusion
(What each experiment tell us?)
1 / Heat-killed S lysate added to R strain bacteria. / Sugar coat, protein, DNA and RNA / Transforming factor is in the lysate.
2 / Added the enzyme SIII to the heat-killed S lysate. This destroyed the sugar coating. / Protein, DNA and RNA
3 / Protein digesting enzymes (trypsin and chymotrypsin) added to the lysate from Experiment 2
4 / Nucleic acids isolated from the lysate in Experiment 3 and dissolved in water. RNA destroyed by adding RNase.
5 / DNase (an enzyme that destroys DNA) added to the nucleic acid solution from Experiment 4.
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Alfred Hershey and Martha Chase’s Bacteriophage Experiments
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Background information: Bacteriophages (phages) are viruses that infect bacteria. They have a very simple structure that consists of DNA surrounded by a protein coat. We knew that after infection, bacteria were “transformed” into virus producing factories.
DNA contains a lot of the element phosphorus but no sulfur. Proteins contain sulfur but no phosphorus.
Experiment Number / Experimental Conditions / Results(Where were the radioactive elements found? Liquid? Bacterial pellet?)
1 /
- Phage DNA was labeled with radioactive phosphorus. The phages were added to unlabeled bacteria.
- Phages were detached from the bacteria by putting the mixture into a blender.
- The mixture was spun in a centrifuge. The heavy bacteria fall to the bottom. The phage remain “suspended” in the liquid.
2 /
- Phage protein was labeled with radioactive sulfur. The phages were added to unlabeled bacteria.
- Phages were detached from the bacteria by putting the mixture into a blender.
- The mixture was spun in a centrifuge. The heavy bacteria fall to the bottom. The phage remain “suspended” in the liquid.
What was learned from this experiment?
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The Structure of DNA: James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin
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What information did Watson, Crick, Wilkins and Franklin have about the structure of DNA before they began their investigations?
What additional things did we learn about the structure of DNA by the end of their investigations?
Jennifer Shake, Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, 2013