A student made the following table to summarize what he had learned about bacterial transcriptional control mechanisms. A fellow classmate pointed out that the table is not accurate. Which statement describes the problem? $$\begin{array} { | l | c | c | c | }
\hline & \begin{array} { c }
\text { Type of } \
\text { regulatory } \
\text { protein }
\end{array} & \begin{array} { c }
\text { Operon } \
\text { transcriptional } \
\text { response to wild- } \
\text { type regulatory } \
\text { protein }
\end{array} & \begin{array} { c }
\text { Operon transcriptional } \
\text { response to mutated } \
\text { regulatory protein } \
\text { (rendered nonfunctional) }
\end{array} \
\hline \text { Positive control } & \text { Activator } & \text { On } & \text { Off } \
\hline \text { Negative control } & \text { Repressor } & \text { Off } & \text { Off } \
\hline
\end{array}$$

Question

A student made the following table to summarize what he had learned about bacterial transcriptional control mechanisms. A fellow classmate pointed out that the table is not accurate. Which statement describes the problem? $$\begin{array} { | l | c | c | c | } 
\hline & \begin{array} { c } 
\text { Type of } \
\text { regulatory } \
\text { protein }
\end{array} & \begin{array} { c } 
\text { Operon } \
\text { transcriptional } \
\text { response to wild- } \
\text { type regulatory } \
\text { protein }
\end{array} & \begin{array} { c } 
\text { Operon transcriptional } \
\text { response to mutated } \
\text { regulatory protein } \
\text { (rendered nonfunctional) }
\end{array} \
\hline \text { Positive control } & \text { Activator } & \text { On } & \text { Off } \
\hline \text { Negative control } & \text { Repressor } & \text { Off } & \text { Off } \
\hline
\end{array}$$

Quizplus · Accepted Answer

In negative control systems, a repressor protein binds to the DNA and inhibits transcription. If the repressor is mutated and rendered nonfunctional, it cannot bind to the DNA, thus allowing transcription to occur, which means the operon transcriptional response would be turned on, not off as indicated in the table.

A Student Made the Following Table to Summarize What He