Arizona State University (ASU) MIC 205 Microbiology Exam 1 Practice

The main idea being tested is what kind of molecule carries genetic information in bacteriophages, as shown by the Hershey-Chase experiment.

In this classic study, two parallel phage labeling approaches were used. One set labeled DNA with radioactive phosphorus (32P) and the other labeled protein with radioactive sulfur (35S). After the phages infected E. coli, the researchers used a blender to separate the empty phage coats from the bacterial cells and then measured where the radioactivity ended up. They found that the radioactivity inside the bacteria (and in the progeny phages that formed) came from the DNA label, not the protein label. The protein labels stayed with the outside coats and did not enter the bacterial cells to direct replication. This shows that the genetic information required to produce new phages resides in the DNA, not in the protein.

RNA or lipids were not implicated by this experiment—the results specifically demonstrate DNA as the genetic material for bacteriophages.