[Campbell Biology P.365] The "WHAT IF?" question in the text asks: "How would the results ha... | Practice Question

The "WHAT IF?" question in the text asks: "How would the results have differed if proteins carried the genetic information?" Based on your understanding of the Hershey-Chase experiment, what would be the expected observation regarding the distribution of radioactivity in Batch 1 ³⁵S labeled and Batch 2 ³²P labeled after centrifugation if proteins, not DNA, were the genetic material?

  • A: Batch 1 (³⁵S): radioactivity found in the pellet; Batch 2 (³²P): radioactivity found in the liquid.
  • B: Batch 1 (³⁵S): radioactivity found in the liquid; Batch 2 (³²P): radioactivity found in the pellet.
  • C: Both Batch 1 (³⁵S) and Batch 2 (³²P) would show radioactivity primarily in the pellet.
  • D: Both Batch 1 (³⁵S) and Batch 2 (³²P) would show radioactivity primarily in the liquid.

Explanation

If proteins carried the genetic information, then the ³⁵S-labeled proteins, being the genetic material, would enter the bacterial cells to reprogram them. Consequently, after centrifugation, the ³⁵S radioactivity would be found predominantly in the pellet containing the bacterial cells . Conversely, the ³²P-labeled DNA, which would not be the genetic material in this hypothetical scenario, would remain largely outside the bacterial cells and thus be found in the liquid supernatant after centrifugation. This is the exact opposite of the actual results obtained by Hershey and Chase, which showed DNA as the genetic material.