a1.2.14 - the hershey and chase DNA experiment

Question 1

state the experimental question being tested in the hershey and chase experiment.

Answer 1

both protein and nucleic acids are part of the eukaryotic cell nucleus, and prior to 1952 it was unknown which molecule type was responsible for passing genetic information between generations. hershey and chase designed an experiment to test whether proteins or DNA is the hereditary material.

Question 2

outline the procedure of the hershey and chase experiment.

Answer 2

• hershey and chase (H&C) performed their experiments on viruses that infect bacteria called bacteriophages. they incorporated radioactive isotopes of phosphorus and sulfur into phages. DNA contains phosphorus, but not sulfur, whereas protein contains sulfur, but not phosphorus. therefore, when H &C marked phages with radioactive isotopes of those elements, they placed separate, distinguishable tags on the protein and DNA parts of the phages.
• they allowed the phages to replicate by infecting bacteria. by tracking the location of the radioactive tags, H&C showed that phages only injected their DNA into host bacteria, and that the DNA served as the replicating genetic element of phages. the phages did not inject their protein coats into the bacteria; the protein coats remained outside the bacteria adhered to the bacterial membranes.

Question 3

explain how the results of the Hershey and Chase experiment supported the notion of nucleic acids as the genetic material.

Answer 3

the molecule of heredity must be pasted from generation to generation. when Hershey and Chase demonstrated that radioactively tagged DNA is present across generations of bacteriophages and that radioactively tagged protein is not, they demonstrated that nucleic acids must be the genetic material.

Question 4

outline the use of radioisotopes as research tools.

Answer 4

• hershey and chase relied on radioactive isotopes of phosphorus and sulfur in their experiment to determine that DNA is the genetic material. although they had been used on a small scale prior, after World War II the U.S. Atomic Energy Commission began mass-producing radioisotopes, sending shipments of radioactive materials to scientists.
• because they give off energy as they convert to a more stable form, the isotopes allow biologists to track molecules as they move through biological systems.