Case Study

Title: Analyzing the Effect of a Mutation in the Lactose Operon in E. coli

Background Scenario:

The lac operon in Escherichia coli is a classic example of gene regulation. It contains genes involved in lactose metabolism, such as lacZ, lacY, and lacA, and is regulated by a promoter (P), an operator (O), and a repressor protein (LacI). Under normal conditions, when lactose is absent, the LacI protein binds to the operator and inhibits transcription. When lactose is present, it binds to the repressor and prevents it from binding to the operator, allowing transcription to occur.

Recently, a mutation was discovered in a strain of E. coli isolated from a high-lactose industrial environment. Researchers observed that this strain overproduces β-galactosidase (the enzyme encoded by lacZ) even in the absence of lactose.

Your Task:

You are a molecular biologist assigned to investigate how this mutation affects gene regulation in the lac operon.

Assessment Questions:

Section A: Understanding the Mutation (Comprehension)

1. Based on the overproduction of β-galactosidase, which part of the lac operon is most likely mutated (e.g., promoter, operator, lacI)? Justify your answer.

2. Propose a specific mutation that could lead to the observed phenotype. For example, a base substitution or deletion – describe its likely effect.

Section B: Functional Analysis (Application & Analysis)

3. Predict the effect of this mutation on mRNA transcription and β-galactosidase production with and without lactose. Create a table to support your answer.

4. Design a laboratory experiment to confirm whether the operator or the lacI gene is mutated. Briefly describe the methodology (e.g., reporter gene, gene knockout, complementation test).

Section C: Broader Implications (Evaluation)

5. Explain how such a mutation could affect the bacteria's fitness in:

   • A high-lactose environment

   • A low-lactose environment

6. What are the potential implications of this regulatory mutation for biotechnology applications?

Marking Criteria (Rubric):