Question

In an experiment, bacteria were infected with 32P labeled virus in a ratio of 5:1. The culture was vigorously shaken followed by centrifugation. Radioactivity was
A. Lost due to metabolic activity.
B. Detected in the supernatant as inorganic phosphate.
C. Detected in the supernatant in association with viral capsid.
D. Detected in bacterial cell pellets.

Answer 1

Hint: An experiment in bacteria with radioactively labeled viruses was done by Alfred Harshey and Martha Chase in 1952. Their experiment was totally based upon the biology of a virus known as bacteriophage T2, this virus attacks bacteria. The virus contains either DNA or RNA as their genetic material along with protein. DNA is packed inside a coat of protein.

Complete answer:
- With the help of the search of genetic material for an inheritance, Frederick Griffith concluded that one strain of bacteria was physically transformed by the heat-killed another strain of bacteria by transferring some transforming principle. The transforming principle was the genetic material.
- Alfred Harshey and Martha Chase in 1952 worked on viruses that infected bacteria called bacteriophages, to prove that the DNA is the genetic material.
- When bacteriophage is attached to the surface of bacteria, its genetic material is transferred into the bacterial cell. Bacteria treat the genetic material of a virus as its own genetic material and bacteria manufacture more viruses.
- Hershey and Chase worked to discover that the genetic material that enters the bacteria from the virus was protein or DNA.
- Two batches of viruses were grown by them, one with radioactive phosphorus which is found in DNA, and another with radioactive sulfur which is found in DNA.
- A virus that contained radioactive DNA showed radioactivity and infected bacteria whereas the bacteria infected with viruses that contained radioactive protein did not show radioactivity and indicates that viral DNA was passed to infected bacteria.
- Radioactivity was not lost by metabolic activity.

Hence, the correct answer is option (D).

Note: Hershey and Chase worked on the same but longer-term experiments. They allowed the offsprings of viruses to multiply in unlabeled bacteria. When the results were observed viruses contained almost no 35S and parental viral protein was absent. They contain one-third of the original 32P and hence one-third of the original DNA was present. This is because DNA is passed from generation to generation, not protein as the DNA contains the hereditary information and protein does not have such function.