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Question
E. coli was infected with bacteriophage having radioactive (S35) protein in a culture. It was blended, centrifuged and distribution of (S35) determined. What does the experiment show?
E. coli was infected with bacteriophage having radioactive (S35) protein in a culture. It was blended, centrifuged and distribution of (S35) determined. What does the experiment show?
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Solution
The correct option is C Protein is not the genetic material
Part 1: Introduction to the experiment
Bacteriophages attach themselves to specific host bacteria and insert their genetic material into the bacteria.
The genetic material carries all the genetic information related to the structure and function of the virus and can direct the synthesis and assembly of new phage particles.
The genetic material of the virus takes control over the host machinery and directs the host cell to utilise its resources for creating new viral particles.
Like every other virus, bacteriophages are composed of a protein coat and a nucleic acid (DNA or RNA) molecule enclosed within the coat.
The given experiment aims to prove whether the nucleic acid or the protein coat serves as the genetic material for the bacteriophage.
Part 2: Procedure
In the given experiment, a bacteriophage having a protein coat radiolabeled with radioactive S35 is used to infect E.coli cells.
After a while the mixture was blended and centrifuged.
Centrifugation results in the bacterial cells to settle at the bottom of the containers whereas the supernatant, consisting of culture medium and particles outside the bacterial cells, floats above.
The two fractions were then tested for the presence of radioactivity.
Part 3: Result and conclusion
The bacterial cells settled at the bottom of the centrifuge vessels did not show any radioactivity but the supernatant did.
This shows that the protein coat of the bacteriophage did not enter the bacterial cells and was left behind. Thus, it can be concluded that the protein is not the genetic material of the virus.
But, this result does not give any conclusive proof of whether DNA serves as the genetic material or not. This is because the DNA was not radiolabeled and from the obtained results we cannot be sure whether the DNA lies in the cellular debris or the supernatant.
Final answer
(a) Protein is not the genetic material
Part 1: Introduction to the experiment
Bacteriophages attach themselves to specific host bacteria and insert their genetic material into the bacteria.
The genetic material carries all the genetic information related to the structure and function of the virus and can direct the synthesis and assembly of new phage particles.
The genetic material of the virus takes control over the host machinery and directs the host cell to utilise its resources for creating new viral particles.
Like every other virus, bacteriophages are composed of a protein coat and a nucleic acid (DNA or RNA) molecule enclosed within the coat.
The given experiment aims to prove whether the nucleic acid or the protein coat serves as the genetic material for the bacteriophage.
Part 2: Procedure
In the given experiment, a bacteriophage having a protein coat radiolabeled with radioactive S35 is used to infect E.coli cells.
After a while the mixture was blended and centrifuged.
Centrifugation results in the bacterial cells to settle at the bottom of the containers whereas the supernatant, consisting of culture medium and particles outside the bacterial cells, floats above.
The two fractions were then tested for the presence of radioactivity.
Part 3: Result and conclusion
The bacterial cells settled at the bottom of the centrifuge vessels did not show any radioactivity but the supernatant did.
This shows that the protein coat of the bacteriophage did not enter the bacterial cells and was left behind. Thus, it can be concluded that the protein is not the genetic material of the virus.
But, this result does not give any conclusive proof of whether DNA serves as the genetic material or not. This is because the DNA was not radiolabeled and from the obtained results we cannot be sure whether the DNA lies in the cellular debris or the supernatant.
Final answer
(a) Protein is not the genetic material
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