Gene control

Need to know

What you need to know

• **Regulatory gene (lacI)**: Located upstream of the operon, it encodes the *lac* repressor protein, which is constitutively expressed.
• **Promoter (P)**: The binding site for RNA polymerase to initiate transcription of the structural genes.
• **Operator (O)**: A segment of DNA within the promoter where the *lac* repressor binds.
• **Structural genes (lacZ, lacY, lacA)**: These genes code for enzymes involved in lactose metabolism: **β-galactosidase (lacZ)** breaks down lactose into glucose and galactose; **permease (lacY)** is a membrane protein that transports lactose into the cell; and **transacetylase (lacA)** has a role in detoxifying by-products.

Explanation

Gene control

1. **Regulatory gene (lacI)**: Located upstream of the operon, it encodes the *lac* repressor protein, which is constitutively expressed.
2. **Promoter (P)**: The binding site for RNA polymerase to initiate transcription of the structural genes.
3. **Operator (O)**: A segment of DNA within the promoter where the *lac* repressor binds.
4. **Structural genes (lacZ, lacY, lacA)**: These genes code for enzymes involved in lactose metabolism: **β-galactosidase (lacZ)** breaks down lactose into glucose and galactose; **permease (lacY)** is a membrane protein that transports lactose into the cell; and **transacetylase (lacA)** has a role in detoxifying by-products.