Biology Experiment

Question

Explain how the following experiment provided support for the claim that DNA is the primary source of heritable information.

Two experiments are run side by side:

1. One set of virus particles is labeled with the sulfur-35 isotope. A second set is labeled with phosphorus-32 isotope.

2. Each set of labeled virus particles is incubated with different batches of the same bacteria.

3. Following infection of the bacteria by the virus particles, the bacteria are separated from the virus particles by agitation in a blender.

4. The bacterial cells are separated from the virus particles by centrifugation.

5. The supernatant and pellet (two separated components) from each batch are analyzed to determine the locations of the isotope labels.

Results:

1. Radioactive sulfur is found in the supernatant.

2. Radioactive phosphorus is found in the cell pellet.

3. A new generation of viable virus particles emerge from the bacteria cells when they are reconstituted in liquid culture.

Answer 1

Hello,

This problem describes the classic Hershey-Chase experiment that showed DNA, not protein, was the source of hereditary material. Whichever radioactive material that ultimately remained with the bacteria was likely the source of hereditary material, since the virus was known to incorporate into the hereditary material of the bacterial hosts to replicate. The radioactive sulfur-labeled protein was found in the supernatant separated from the bacterial pellets because the viral protein was simply structural in nature and was not incorporated into the bacterial hosts. The radioactive phosphorous-labeled DNA remained with the bacterial pellet because the genetic information of the virus, DNA, was incorporated into the genetic material of the host cell. Viable virus was recovered when the bacteria were placed back into fresh media because the genetic instructions of the virus remained with the host.