For a Science Fair Project, Two Students Decided to Repeat

question 19

Multiple Choice

For a science fair project, two students decided to repeat the Hershey and Chase (1952) experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labelling the nitrogen atoms would provide a stronger signal than labelling the phosphates. Why won't this experiment work?

• A) There is no radioactive isotope of nitrogen.
• B) Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long.
• C) Although there are more nitrogens in a nucleotide, labelled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
• D) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

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