9700 · 16.3
Gene control
Welcome to **Gene Control**, a pivotal topic in A Level Biology that explains how organisms manage the expression of their genetic information. Every cell in your body, from a skin cell to a nerve cell, contains the exact same DNA, yet they look and function completely differently. How? Through intricate mechanisms of **gene regulation**. This lesson will equip you with the knowledge to ace questions on both prokaryotic and eukaryotic gene control, covering everything from the classic **lac operon** to the complexities of **epigenetics** and **microRNA**. Key points align with **A-Level Notes** 9700 Biology chapter **16** (topic **16.3**).
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
- **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.