For a science fair project, two students decided to repeat the hershey and chase 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, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. why won't this experiment work?
a. radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long.
b. there is no radioactive isotope of nitrogen.
c. although there are more nitrogens in a nucleotide, labeled 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.

B. There is no radioactive isotope of nitrogen.

Explanation:

It is not all isotopes of elements that are radioactive. Nitrogen-14 and Nitrogen-15 are stable. They are not radioactive. Therefore, they cannot be detected the way Phosphorus-32 will be detected.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.