(a) Why did Hershey and Chase use radioactive P32 and S35 in their experiments? Explain.
(b) Following the experiments conducted by them, write what conclusion did they arrive at and how. [5 marks]
(a) Why did Hershey and Chase use radioactive P32 and S35 in their experiments? Explain.
(b) Following the experiments conducted by them, write what conclusion did they arrive at and how. [5 marks]
(a) Hershey and Chase used radioactive P32 to label the DNA because phosphorous was present only in DNA and not proteins. [1 mark]
They used S35 to label the proteins because sulphur was present only in proteins and not DNA. [1 mark]
(b) Hershey and Chase performed two sets of experiments simultaneously. In one set, they allowed Bacteriophages labelled with P32 to infect a culture of E. coli.
In the second set, they allowed bacteriophages labelled with S35 to infect a culture of E.coli.Radioactively labelled phages were allowed to infect to E. coli bacteria by incubating for a specific time. After incubation, the viral coats were removed from the bacteria by agitating them in a blender. The viral coats were separated from the bacteria by spinning them in a centrifuge. The viral particles sedimented to the bottom of the tubes and bacteria was present in the supernatant.
They checked both the tubes for the presence of radioactivity. In the first set, bacteria which was infected with P32 labelled viruses exhibited radioactivity, indicating that DNA was the material that passed from the virus to the bacteria.
Bacteria that were infected with S35 labelled viruses did not exhibit radioactivity.
This indicates that S35 labelled viral proteins did not enter the bacteria. Only the DNA with labelled phosphorus entered the bacteria. They concluded that DNA was the genetic material that was passed from the virus to the bacteria. [3 marks]
(a) Hershey and Chase used radioactive P32 to label the DNA because phosphorous was present only in DNA and not proteins. [1 mark]
They used S35 to label the proteins because sulphur was present only in proteins and not DNA. [1 mark]
(b) Hershey and Chase performed two sets of experiments simultaneously. In one set, they allowed Bacteriophages labelled with P32 to infect a culture of E. coli.
In the second set, they allowed bacteriophages labelled with S35 to infect a culture of E.coli.Radioactively labelled phages were allowed to infect to E. coli bacteria by incubating for a specific time. After incubation, the viral coats were removed from the bacteria by agitating them in a blender. The viral coats were separated from the bacteria by spinning them in a centrifuge. The viral particles sedimented to the bottom of the tubes and bacteria was present in the supernatant.
They checked both the tubes for the presence of radioactivity. In the first set, bacteria which was infected with P32 labelled viruses exhibited radioactivity, indicating that DNA was the material that passed from the virus to the bacteria.
Bacteria that were infected with S35 labelled viruses did not exhibit radioactivity.
This indicates that S35 labelled viral proteins did not enter the bacteria. Only the DNA with labelled phosphorus entered the bacteria. They concluded that DNA was the genetic material that was passed from the virus to the bacteria. [3 marks]
