Biology
Chapter 10 DNA, RNA, and Protein Synthesis
Notes Outline
Section 10-1 Discovery of DNA
Objectives

Relate how Griffith’s bacterial experiments showed that a hereditary factor was involved in transformation.

Summarize how Avery’s experiments led his group to conclude that DNA is responsible for transformation in
bacteria.

Describe how Hershey and Chase’s experiment led to the conclusion that DNA, not protein, is the hereditary
molecule in viruses.
Griffith’s Experiments
1. British medical officer Frederick Griffith was studying a bacterium called Streptococcus pneumoniae (abbreviated
S. pneumoniae). Griffith was trying to develop a vaccine against a disease-causing, or virulent, strain of the
bacterium.
2. Each virulent bacterium was surrounded by a capsule made of polysaccharides that protects it from a body’s
defense systems. The bacteria in the virulent strain grow as smooth-edged colonies when grown in a Petri dish
and are called the S strain.
3. The second strain of S. pneumoniae does not cause pneumonia and lacks a capsule. When grown in a Petri dish,
the R strain grows into rough colonies.
4. Griffith used the two strains of S. pneumoniae in a series of four experiments.
a. In Experiments 1 and 2, Griffith injected either live R or live S cells into mice. He found that only S cells
killed the mice.
b. In Experiment 3, he injected mice with heat-killed S bacteria and found that the mice survived.
c. In Experiment 4, he injected mice with heat-killed S cells and live R cells and found that the mice died.
5. Griffith’s experiments showed that hereditary material can pass from one bacterial cell to another.
6. The transfer of genetic material from one cell to another cell or from one organism to another organism is called
transformation.
Avery’s Experiments
7. American researcher Oswald Avery and his colleagues set out to test whether that transforming agent in
Griffith’s experiments was protein, RNA, or DNA.
8. The scientists used enzymes to separately destroy each of these three molecules in heat-killed S cells.
a. In Experiment 1, they used a protease enzyme to destroy protein in the heat-killed cells.
b. In Experiment 2, they used RNase to destroy RNA in the heat-killed cells.
c. In Experiment 3, they used DNase to destroy DNA in the heat-killed cells.
9. Then, they separately mixed the three experimental batches of heat-killed S cells with live R cells and injected
mice with the mixtures.
10. Avery and his group found that the cells missing protein and RNA were able to transform R cells into S cells and
kill the mice. However, cells missing DNA did not transform R cells into S cells, and the mice survived.
11. Avery’s work showed that DNA is the hereditary material that transfers information between bacterial cells.
Hershey-Chase Experiment
12. Americans Alfred Hershey and Martha Chase set out to test whether DNA or protein was the hereditary material
that viruses transfer when viruses enter a bacterium.
13. Viruses that infect bacteria are called bacteriophages, or phages.
14. Hershey and Chase used radioactive isotopes to label protein and DNA in the phage.
a. In Experiment 1, they used radioactive sulfur to label protein.
b. In Experiment 2, they used radioactive phosphorus to label DNA.
15. Then, they allowed protein-labeled and DNA-labeled phage to separately infect E. coli.
16. They removed the phage coats from the cells in a blender, and then used a centrifuge to separate the phage
from the E. coli.
17. They found that all of the viral DNA and very little of the protein had entered the E. coli cells.
18. Hershey and Chase confirmed that DNA, and not protein, is the hereditary material.
*** Assignment: Answer the 10-1 Section Review Questions #1-6 on page 195.