Question

6.) In the 1952 Hershey-Chase experiment showed that DNA is the genetic material of bacteriophage. Explain where the protein labeled with 35S ended up and where the DNA labeled with 32P ended up after centrifugation in their experiment. a. Draw a diagram of the experiment in support of your explanation. b. Is it possible to do the reverse labeling? (protein labeled with 32P and DNA is labeled with 35S) Why or why not?

7.) For each base-pair set, state if the two pairs are distinguishable using the minor groove, the major groove, or both. a. G:C vs. C:G ________ b. A:T vs. G:C _________

c. A:T vs. T:A _________

8.) Ethidum bromide (EtBr) is a large flat, multiringed cation. Its flat shape allows it to insert itself between the stacked base pairs of double stranded (dsDNA). Because it fluoresces when exposed to UV light and because its fluorescence increases dramatically after intercalation, it is used as a stain to visualize DNA. When ethidium intercalates it causes the DNA to unwind by about 26 degrees, reducing the normal rotation per base pair, decreasing the twist (T) of the DNA.

a. What effect would this change have on the writhe (W) of the plasmid?

b. When EtBr is used to visualize a relaxed covalently closed circular plasmid by gel electrophoresis, what effect would this have on the migration of the plasmid?

Answer 1

ANSWER 1.

In the Hershey Chase experiment, bacteria were infected with two types of phages. The first type of phage had labelled P-32 while the other type of phage had labelled S-35.

After infection, blending was done.

Then centrifugation was done. After centrifugation, it was found that S-35 is present in the solution while P-32 is not present. This means that P-32 has gone inside the cell after infection. On the other hand, S-35 has not gone inside the cell.

Note that S-35 labelling is done on the viral coat while P-32 labelling is done on the DNA. So, the above results also imply, that DNA (labelled) entered the bacterial cell while the protein coat did not enter.

ANSWER a)

ANSWER b)

Note that it is not possible to do reverse labelling because neither DNA contains sulfur nor protein contains phosphorus. Protein contains amino group, alkyl group, and carboxyl group.