# The Lac Operon ![[The Lac Operon-1.png]] The *lac Operon* is a **negative inducible** operon most notably used by *E. coli* to metabolize lactose molecules within the human gut. lacO is the operator region > [!summary] Activation of lac repressor > 1. Add lactose to the cell culture > 2. Lactose binds to the lac repressor > 3. RNA polymerase moves from the lac promoter and starts transcribing the mRNA > 4. LacZ produces $\beta$-galactosidase, lacY produced Lactose permease, and lacA produced thiogalactoside transacetylase --- ## The Lac Genes ![[Operons.png|400]] **Structural Genes** - lacZ codes for $\beta$-Galactosidase - Breaks down lactose into glucose and galactose - Can also convert lactose into allolactose - lacY codes for Permease - allows for the active transportation of lactose molecules through the cell membrane that would typically be too large to enter passively - lacA codes for Transacetylase - unknown function (sick) **Regulatory Genes** - lacI: The protein created from the lacI gene is a repressor that will bind to the promoter/operator region of the lac operon and prevent transcription. --- There is also a **positive control** related to the *lac operon* that can increase its expression. While prokaryotes are capable of metabolizing lactose for energy, they prefer to use glucose as it can permeate into the cell and enter the glycolysis process without the need for active transport (Permease) that would require energy **Catabolite activator protein (CAP)** is a *trans-acting* regulator that binds to a 22-nucleotide region upstream of the lac operon's promoter This CAP protein makes it much easier for RNA polymerase to locate and bind to the promoter region of the lac operon and thus increases the expression of the structural genes >tl;dr CAP and cAMP increase the transcription of the lac operon, however the presence of glucose will inhibit the function of cAMP and lead to an overall reduction of the lac operon within the cell (although it won't fully disable it)