Mutations can alter the function of the lac operon (see Module 11.1). Predict how the following mutations would affect the function of the operon in the presence and absence of lactose: a. Mutation of regulatory gene; repressor cannot bind to lactose. b. Mutation of operator; repressor will not bind to operator. c. Mutation of regulatory gene; repressor will not bind to operator. d. Mutation of promoter; RNA polymerase will not attach to promoter.

Verified step by step guidance

1. Understand the normal function of the lac operon: The lac operon is a set of genes that are responsible for the metabolism of lactose in bacterial cells. It includes a promoter (where RNA polymerase binds), an operator (where the repressor binds), and three structural genes (lacZ, lacY, lacA). The operon is regulated by a repressor protein that is coded by a regulatory gene. In the absence of lactose, the repressor binds to the operator, preventing transcription. When lactose is present, it binds to the repressor, causing a conformational change that prevents the repressor from binding to the operator, allowing transcription to proceed.
2. Analyze mutation a (Mutation of regulatory gene; repressor cannot bind to lactose): In this scenario, even if lactose is present, the repressor cannot bind to it and undergo the necessary conformational change. This means the repressor will remain bound to the operator, blocking transcription of the lac operon both in the presence and absence of lactose.
3. Analyze mutation b (Mutation of operator; repressor will not bind to operator): With this mutation, the repressor cannot bind to the operator regardless of lactose presence. This results in continuous transcription of the lac operon genes, as there is no repression mechanism in place to stop RNA polymerase, both in the presence and absence of lactose.
4. Analyze mutation c (Mutation of regulatory gene; repressor will not bind to operator): Similar to mutation b, this mutation prevents the repressor from binding to the operator. Consequently, transcription of the lac operon will occur continuously, irrespective of whether lactose is present or not.
5. Analyze mutation d (Mutation of promoter; RNA polymerase will not attach to promoter): This mutation affects the binding site of RNA polymerase. Without the ability of RNA polymerase to bind to the promoter, transcription of the lac operon cannot initiate, leading to no expression of the operon's genes both in the presence and absence of lactose.