Fig. 6.1 illustrates that the $\textit{lac}$ operon includes structural genes and regulatory sequences. Use Fig. 6.1 to pick out two structural genes. Complete Table 6.1 by naming each structural gene and its product.
Gene I is transcribed continuously so that its protein is made. This is constitutive expression. Explain why some genes show constitutive expression.
Describe how the product of gene I affects the functioning of the $\textit{lac}$ operon.
If $E.\ coli$ is placed in a nutrient medium that contains lactose, some new enzymes are made. These are called inducible enzymes. Explain what is meant by an inducible enzyme.
The structural genes of the $\textit{lac}$ operon are not expressed when lactose is absent. Suggest one reason why this benefits $E.\ coli$.