6.1.3 Gene Control: Lac Operon Flashcards
Regulatory genes definition
Code for a repressor protein which regulates expression structural genes
Structural gene definition
Codes for a protein with a particular structure and function in a cell
What is an operon?
- A group or cluster of genes
- Controlled by the same promoter
What enzyme does the lac operon control the production of?
Lactase
What does lactase do?
Breaks down lactose to be used as an energy source in bacteria
How is lactase an inducible enzyme?
Only synthesized when lactose is present (helps bacteria avoid wasting energy producing an enzyme when there is no substrate to break down)
Structure of Lac Operon from left to right
What is the operator?
- Segment of DNA where repressor protein binds to
- In order to inhibit the transcription of a gene which would produce a structural protein
What is the promoter?
Site where RNA polymerase binds to in order to transcribe a gene into a structural protein
Lac repressor protein structure
- 2 binding sites
- 1 for operator, 1 for lactose
- When bound to operator, transcription of lactase is prevented
- When bound to lactose, the shape of the repressor protein distorts, and can no longer bind to the operator
What happens when lactose is absent?
- Regulatory gene transcribed and translated to produce lac repressor protein
- Lac repressor protein binds to operator region of lac operon
- It’s presence means RNA polymerase cannot bind to the promoter region
- So transcription of structural genes for lactase does not occyur
- Lactase is not synthesised
What happens when lactose is present?
- Lactose binds to 2nd binding site of lac repressor protein
- Shape of protein is distorted so it cannot bind to the operator site
- So RNA polymerase can bind to the promoter region
- Transcription of the structural gene for lactase happens
- Lactase is synthesised
- Lactase can break down lactose which can be used for energy by the bacteria
