Question

In an experiment, bacteria were infected with ${}^{32}P$ labeled virus in a ratio of $5:1$. The culture was rigorously shaken followed by centrifugation. Radioactivity was

• A. Lost due to metabolic activity.
• B. Detected in supernatant as inorganic phosphate.
• C. Detected in the supernatant in association with viral capsid.
• D. Detected in bacterial cell pellet.

Answer 1

The correct option is D Detected in bacterial cell pellet.

The search of genetic material for inheritance led Frederick Griffith conclude that one strain of bacteria was physically transformed by the heat killed another strain of bacteria by transferring some. ‘transforming principle’. This transforming principle was thought to be the genetic material. To prove that the DNA is genetic material Alfred Harshey and Martha Chase in 1952 worked with viruses,that infected bacteria, called bacteriophages.

The bacteriophage attaches to the bacteria and its genetic material enters the bacterial cell. The viral genetic material is treated by bacteria as its own genetic material and more viruses are manufactured by bacteria. Harshey and Chase worked to discover whether it was protein or DNA from virus that entered the bacteria.

They grew two batches of viruses , one with radioactive sulphur which is found in proteins and another with radioactive phosphorus which is found in DNA .Radioactive phases were allowed to infect bacteria, as infection sets in, the viral coats were removed by agitating them in blender and viral particles were separated by vigorous spinning . Bacteria infected with viruses that contained radioactive DNA showed radioactivity while bacteria infected with viruses that contained radioactive protein did not show radioactivity,indicating that viral DNA was passed to infected bacteria.

Option D is correct.