Hershey-Chase Experiment & DNA Entry — NEET Biology

Correct answer: D — S2, S3 and S5 only

The Hershey and Chase experiment provided unequivocal proof that DNA is the genetic material. Let's evaluate each statement: S1: Incorrect. Viruses were grown in a medium containing radioactive sulfur (35S) to label viral *proteins*, not DNA, because proteins contain sulfur (in amino acids like methionine and cysteine) while DNA does not. DNA was labeled with radioactive phosphorus (32P). S2: Correct. Viruses grown in the presence of radioactive phosphorus (32P) contained radioactive DNA because DNA contains phosphorus in its backbone, but not radioactive protein, as proteins lack phosphorus. S3: Correct. When bacteria were infected with 35S labeled viruses, the radioactive protein coats remained outside the bacterial cells. After agitating in a blender and centrifugation, the lighter viral coats (containing 35S) were found in the supernatant, while the heavier bacterial cells (without 35S) formed a pellet. S4: Incorrect. The experiment concluded that *DNA* (labeled with 32P) entered the bacterial cells, not protein (labeled with 35S). This was the key finding that established DNA as the genetic material. S5: Correct. Centrifugation was used to separate the infected bacterial cells (which formed a pellet at the bottom) from the lighter viral particles and their empty coats (which remained in the supernatant). Therefore, statements S2, S3, and S5 are correct. The experiment clearly showed that DNA, not protein, was passed from the virus to the bacteria, thus confirming DNA as the genetic material.