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Molecular Biology, 4/e
Robert F. Weaver
The Molecular Nature of Genes

Hershey and Chase Experiment

Why are radioactive isotopes a valuable tool in molecular biology? Molecular biology mostly takes place on a scale too small to be directly observed by researchers. While cells, organelles, and even macromolecules can be visualized with high-powered microscopes, the molecular processes that drive biology cannot be seen and need to be inferred from experiments. Radioactive isotopes are versions of elements such as carbon, nitrogen, or phosphorus that unstable and release neutrons to become more stable isotopes. The radioactive signal given off by the emission of neutrons allows scientists to detect the isotopes even when they cannot be seen. Adding isotopes to biological systems allows scientists to trace both molecular pathways and the locations at which these pathways occur.

View the animation below, then complete the quiz to test your knowledge of the concept.



1

What part of the phage entered the bacterial cell following infection?
A)DNA
B)RNA
C)protein coat
D)the entire phage
E)no part
2

If 35S was found in progeny phages rather than 32P, Hershey and Chase would have concluded that
A)proteins contain phosphorus.
B)DNA contains sulfur.
C)phage DNA enters the host cell.
D)phage protein enters the host cell.
E)phage can kill the E. coli cell.
3

In the Hershey and Chase experiment, radioactively-labeled
A)32P did not enter the cell.
B)32P remained inside the cells after vigorous shaking.
C)32P was removed from the cells by vigorous shaking.
D)32P and 35S remained inside the cells after vigorous shaking.
E)32P and 35S were removed from the cells after vigorous shaking.
4

Hershey and Chase labeled the phage DNA with radioactive 32P.
A)True
B)False
5

The phage used in the experiment consisted of a DNA molecule surrounded by a protein coat.
A)True
B)False








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