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Questions
Answer the following questions based on Hershey and Chases's experiments:
(a) Name the kind of virus they worked with and why?
(b) Why did they use two types of culture media to grow viruses in ? Explain.
(c) What was the need for using a blender and later a centrifuge during their experiments?
(d) State the conclusion drawn by them after the experiments.
How did Hershey and Chase established that DNA is transferred from virus to bacteria?
Solution 1
a) Hershey and Chase worked on bacteriophages because they have the ability to infect bacteria. When a bacteriophage infects a bacterium, the viral genetic material gets attached with the bacterial genetic material and the bacterium then treats the viral genetic material as its own to synthesise more viral particles.
(b) They grew some phages in a medium with radioactive sulphur, while others in a medium with radioactive phosphorus. The reason behind this was to label DNA and proteins separately in order to indentify which one is acting as genetic material.
(c) Then, they blended E. coli and centrifuged it to remove viral particles and then checked presence of radioactivity.
(d) They observed that the bacteria with radioactive DNA were radioactive, while those with radioactive proteins had lost their radioactivity.
This showed that it is the DNA that enters the bacteria from viruses and not proteins. Hence, it was concluded that DNA is the genetic material.
Solution 2
Hershey and Chase worked on bacteriophages (viruses that infect bacteria).
When a bacteriophage infects a bacterium, the viral genetic material gets attached with the bacterial genetic material and then, bacteria treats the viral genetic material as its own to synthesise more viral particles.
Hershey and Chase worked to discover whether it was a protein or DNA that entered the bacteria from virus.
They labelled some phages with radioactive sulphur and the others with radioactive phosphorus.
These radioactive phages were used to infect E. coli.
Then, E.coli was blended and centrifuged to remove viral particles.
It was observed that bacteria with radioactive DNA were radioactive while those with radioactive proteins lost their radioactivity.
This showed that it is the DNA that enters the bacteria from viruses and not proteins. Hence, it was concluded that DNA is the genetic material.
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