An Epidemic Disease Affecting Sheep Grazing near the Hot Springs

Essay

An epidemic disease affecting sheep grazing near the hot springs of Thermopolis,Wyoming,was found to be due to a new virus.This virus could infect sheep kidney cells cultured in vitro.The virus appeared to contain four chemically defined biomolecules,which we will call W,X,Y,and Z.Investigators wished to determine which of these components carried the genetic information of the virus.

An experiment was conducted in which one of the four components was radioactively labeled in different batches of kidney cells cultured and infected with the virus.Thus,four batches of labeled virus were generated (labeled W,X,Y,or Z).

Radioactive virus from each of these batches was allowed to attach to nonradioactive kidney cells.The cells were centrifuged down to remove the unattached viruses.The cells were then briefly exposed to a vigorous agitation to release viral particles on the cell surface,and again centrifuged.The supernatant (containing shaved-off viral parts)and the pelleted infected cells were examined for radioactivity,with the following results:
% Radioactivity
$$\begin{array} { | l | l | l | l | l | } \hline \text { Labeled component: } & \mathrm { W } & \mathrm { X } &\mathrm { Y } & \mathrm { Z } \\\text { Supermatarit } & { 100 }&0&0&0\\\text { Pelleted cells } & 0 & 100 & 100 & 100 \\\hline\end{array}$$

a)On the basis of these results,which of these components does NOT carry genetic information? Why?

Other experiments revealed that one of these purified biomolecules was contaminating sheep DNA,and the two remaining components did appear to be derived from a virus.The nitrogenous base compositions were as follows:
$$\begin{array} { | l | l | l | l | } \hline \text { Labeled component: } & \mathrm { X } & \mathrm { Y } & \mathrm { Z } \\\% \mathrm {~A}& 21 & 26 & 28 \\\% \mathrm { G } & 21 & 32 & 22 \\\% \mathrm {C } & 32 & 21 & 22 \\\% \mathrm { T } & 0 & 21 & 28 \\\% \mathrm {U} & 26 & 0 & 0 \\\hline\end{array}$$ b)What can you say about the type of nucleic acid found in each of these three components?

c)Can you determine which of these purified biomolecules is most likely sheep DNA and which are more likely to belong to the virus? Explain your response.