[Campbell Biology P.365] In the Hershey-Chase experiment, after the phages infected the bact... | Practice Question

In the Hershey-Chase experiment, after the phages infected the bacterial cells and the mixture was agitated, what was the primary purpose of the centrifugation step, and where was the radioactivity mainly detected for Batch 1 ³⁵S labeled and Batch 2 ³²P labeled , respectively?

  • A: To separate phages from bacterial cells; Batch 1: liquid, Batch 2: pellet.
  • B: To break open bacterial cells; Batch 1: pellet, Batch 2: liquid.
  • C: To isolate genetic material; Batch 1: liquid, Batch 2: liquid.
  • D: To quantify the total amount of radioactive material; Batch 1: pellet, Batch 2: pellet.

Explanation

The centrifugation step in the Hershey-Chase experiment served to separate the denser bacterial cells which formed a pellet at the bottom of the test tube from the lighter phage particles and uninfected phages which remained suspended in the liquid, called the supernatant . For Batch 1, labeled with ³⁵S protein , most radioactivity was found in the liquid supernatant , indicating that the protein did not enter the cells. For Batch 2, labeled with ³²P DNA , most radioactivity was found in the pellet bacterial cells and contents , indicating that the DNA entered the cells.