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The search for the genetic material: DNA is the genetic material sheet
5-mark answer frame

Describe the experiment of Hershey and Chase. How did it prove that DNA is the genetic material?

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · State the aim. To find whether protein or DNA from a phage enters the bacterium and carries the genetic information.
  2. 2 · Label the phages. One set grown with radioactive phosphorus (³²P) to label DNA; another with radioactive sulphur (³⁵S) to label protein.
  3. 3 · Infect, blend and centrifuge. Phages infect E. coli; blending removes the coats; centrifuging settles the bacteria and leaves coats in the supernatant.
  4. 4 · Draw the experiment. [Diagram: two sets, infection, blending, centrifugation, radioactivity in pellet or supernatant]
  5. 5 · Give the result. ³²P was found inside bacteria; ³⁵S stayed in the supernatant.
  6. 6 · Conclude. Only DNA entered the bacteria and made new phages, so DNA is the genetic material.
  7. 7 · Close in one line. So the 1952 blender experiment settled that genes are made of DNA, not protein.

Scoring tip: Say why each isotope labels only one molecule. That reasoning carries a mark.