A research group working with E. coli isolated several lac operon mutants. The group measured $\beta$-galactosidase activity under different environmental conditions, as shown in the table below. Which statement draws a plausible conclusion about one of these mutants?
$$\begin{array} {c}
{ \beta \text { - galactosidase activity } } \
\begin{array} { | c | c | c | }
\hline { \text { Mutant } } &\
& \begin{array} { l }
\text { Glucose present; } \
\text { lactose absent }
\end{array} & \begin{array} { l }
\text { Lactose present; } \
\text { glucose absent }
\end{array} \
\hline \text { I } & 0 & 0 \
\hline \text { II } & + + + & + + + \
\hline \text { III } & 0 & + + + \
\hline \text { IV } & + + + & 0 \
\hline
\end{array}\end{array}$$

Question

A research group working with E. coli isolated several lac operon mutants. The group measured $\beta$-galactosidase activity under different environmental conditions, as shown in the table below. Which statement draws a plausible conclusion about one of these mutants?
$$\begin{array} {c}
 { \beta \text { - galactosidase activity } } \
\begin{array} { | c | c | c | } 
\hline { \text { Mutant } } &\
 & \begin{array} { l } 
\text { Glucose present; } \
\text { lactose absent }
\end{array} & \begin{array} { l } 
\text { Lactose present; } \
\text { glucose absent }
\end{array} \
\hline \text { I } & 0 & 0 \
\hline \text { II } & + + + & + + + \
\hline \text { III } & 0 & + + + \
\hline \text { IV } & + + + & 0 \
\hline
\end{array}\end{array}$$

Quizplus · Accepted Answer

Mutant II shows high levels of F1F1F1S1F1F1F10-galactosidase activity even in the presence of glucose, indicating that the repressor is not binding to the operator to prevent transcription. This suggests a mutation in the repressor gene or the operator region. Mutant I and Mutant III do not show any increase in F1F1F1S1F1F1F10-galactosidase activity in the presence of lactose, indicating that they are unable to produce the enzyme. Mutant IV shows high levels of F1F1F1S1F1F1F10-galactosidase activity in the absence of glucose, indicating that the lac operon is being transcribed, but the F1F1F1S1F1F1F10-galactosidase enzyme is not active, suggesting a mutation in the enzyme gene.

A Research Group Working with E β\betaβ -Galactosidase Activity Under Different Environmental Conditions, as Shown in the Operon

A Research Group Working with E $\beta$ -Galactosidase Activity Under Different Environmental Conditions, as Shown in the Operon