Regulation of Gene Expression - Lac Operon - Unsolved Practice Set
Chapter: Molecular Basis of Inheritance | Topic: Regulation of Gene Expression Lac Operon
REGULATION OF GENE EXPRESSION - LAC OPERON - UNSOLVED PRACTICE SET
Topic: Regulation of Gene Expression Lac Operon
Multiple Choice Questions
Q1. The lac operon is a classic example of gene regulation found in:
- Humans
- E. coli (a prokaryote)
- Yeast
- Pea plants
Q2. The three structural genes of the lac operon (lacZ, lacY, lacA) together code for enzymes involved in the metabolism of:
- Glucose
- Lactose
- Sucrose
- Starch
Q3. In the absence of lactose, the lac repressor protein:
- Binds to the operator and blocks transcription
- Binds to the promoter and enhances transcription
- Has no effect on transcription
- Degrades the structural genes
Q4. The molecule that acts as the inducer of the lac operon, switching it "on" in the presence of lactose, is:
- Glucose
- Allolactose (a lactose derivative)
- ATP
- RNA polymerase
Q5. The lac operon is regulated by which type of control mechanism?
- Positive regulation only
- Negative regulation (through a repressor)
- No regulation at all
- Regulation by DNA polymerase
Short Answer Questions
Q6. What is an operon? Name the three structural genes found in the lac operon.
Q7. What is the role of the lac repressor protein in the absence of lactose?
Q8. What happens to the lac repressor when lactose (or its derivative, allolactose) is present in the cell?
Q9. Why is the lac operon considered an example of "inducible" gene expression?
Long Answer Questions
Q10. Describe the structure of the lac operon, explaining the roles of the regulatory gene, promoter, operator, and structural genes.
Q11. Explain how the lac operon switches between the "on" and "off" states depending on the presence or absence of lactose in the environment.
APPLICATION / ANALYSIS
Q12. A bacterial culture is grown in a medium containing only glucose, with no lactose present. Based on your understanding of the lac operon, predict whether the structural genes (lacZ, lacY, lacA) would be actively transcribed, and explain why.
Q13. A mutant strain of E. coli has a non-functional lac repressor protein that cannot bind to the operator at all, even in the absence of lactose. Predict what effect this mutation would have on the expression of the lac operon genes, and explain your reasoning.