Explore how mutations in lacI, the operator, and the structural genes affect production of LacZ, LacY and LacA. Add or remove lactose, test haploid strains, or build partial diploids to investigate induction and cis- and trans-acting regulation.
🧬 Challenge yourself
Do not just watch the operon. Make the cell do something. Choose a phenotype, design a genotype that should produce it, then use the simulator to test your reasoning.
1Choose genetic configuration
Copy 1 — chromosomal operon
Copy 2 — F′ lac operon
Growth condition
Lactose/allolactose can inactivate I⁺ repressor. There is no IPTG or glucose in this model.
What's happening in the cell?
Lactose present
LacI⁺ + lactose → inactive
lacZYA mRNA
LacZ β-galactosidase
LacY permease
LacA transacetylase
Quick genotypes to try
2Experimental results
lacZ / LacZ
β-galactosidase
—
lacY / LacY
lactose permease
—
lacA / LacA
transacetylase
—
WT reference — lactose present: LacZ ≈ 50 RU · LacY ≈ 50 RU · LacA ≈ 50 RU. In a partial diploid, two active functional copies can approach ≈100 RU.
Ready. Change the genotype and watch the regulatory diagram update. Run the culture to collect quantitative enzyme data.
3Experiment log
#
Configuration
Lactose
Copy 1
Copy 2
LacZ
LacY
LacA
Interpretation
Experiments will appear here. Each interpretation will have the full width it needs to remain readable.
Model note: This teaching simulation focuses on classic lac-operon logic with lactose as the inducer. LacI products act in trans; Oᶜ acts in cis. I⁺ represses O⁺ when lactose is absent and is inactivated when lactose is present. Iˢ is modeled as dominant over I⁺ at O⁺ because the superrepressor cannot be inactivated by lactose. Structural-gene mutant alleles produce no functional product from that copy. Values are relative units with modest experimental noise.
Instructor answer key
Enter the instructor password to reveal the answer for the selected challenge.