Question

If you repeat the Hershey-Chase experiment with ³⁵S- or ³²P-labeled influenza virus, which radioisotope do you expect to find inside the infected host cell?

A. 35S
B. 32P
C. Both radioisotopes
D. Neither

Answer 1

The Hershey Chase experiments showed that when bacteriphages infect bacterial cells it is primarily DNA that is transferred from the bacteriphage to the bacterial cell and not protein. Proteins are then synthesised in the bacterial cell using the host cell machinery and amino acids.

Hence 35S labelling of a bacteriophage particle labelled all the protein of the virus i.e. its protein coat whereas 32P labelling labels the nucleic acid component of the virus i.e.DNA. Hence upon infection, only the DNA is injected into the bacterial cell and the viral coat is left outside the host cell. Therefore only 32P labelled viral nucleic acid will be found inside the infected host cell. (Case of original experiment)

Now coming to the question, the small variation of using influenza viruses will change the outcome of this experiment. Influenza viruses have an outer lipid envelope and instead of injecting DNA into the host cell, their lipid envelope actually fuses with the host cell membrane (since they are mammalian viruses and will infect animal cells) and upon fusion, the protein capsid and nuclear material contained within it is simply released into the host animal cell. Hence in this case the answer will be C. Both Radioisotopes as 35S labelled protein and 32P labelled nucliec acid will both be released inside the host cell.