Question

E. coli cells infected with bacteriophages having radioactive phosphorus are grown on medium containing normal phosphorus and sulphur and their daughter cells are centrifuged. What will be detected in the supernatant after centrifugation?

• A. Normal sulphur
• B. Radioactive sulphur
• C. Normal phosphorus
• D. Radioactive phosphorus

Hint:

Phosphorus is found in DNA and sulphur in protein. Only the phage DNA enters the bacterium, so decide what remains outside in the supernatant.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
In the Hershey-Chase type experiment, phosphorus labels the DNA and sulphur labels the protein coat of the phage.

Step 2: What enters the bacterium
Only the radioactive phage DNA enters the E. coli cells. The empty protein coats (ghosts) remain outside.

Step 3: Centrifugation
The heavier bacterial cells settle as the pellet along with the radioactive phosphorus. The lighter coats stay in the supernatant.

Step 4: Conclusion
The coats contain only normal sulphur in this case, so normal sulphur is detected in the supernatant and no radioactivity.

Final Answer:
Normal sulphur is detected in the supernatant. \[ \boxed{\text{(A) }\text{Normal sulphur}} \]