Unit 4 - Ch. 16: Genetic Regulation in Prokaryotes Flashcards
What is constitutive gene expression?
Genes that are always ON, needed constantly
What is regulated gene expression?
Genes are turned ON/OFF based on cellular needs
What is an operon?
A cluster of genes under one promoter transcribed as polycistronic mRNA
What does the lac operon do?
Controls lactose metabolism in E. coli.
What are the structural genes in the lac operon?
- lacZ: β-galactosidase
- lacY: permease
- lacA: transacetylase
What is lacI?
A repressor protein that blocks the lac operon when lactose is absent
What happens in a lacI⁻ mutant?
The operon is always ON (constitutive expression)
What did Jacob and Monod discover about lacI?
It is a trans-acting repressor, and its mutant version cannot bind the operator
What is a cis-acting element?
A DNA sequence like the operator that must be on the same molecule to affect expression
What is catabolite repression?
Glucose inhibits the lac operon even if lactose is present
What protein activates the lac operon when glucose is low?
CAP (Catabolite Activator Protein)
What molecule allows CAP to bind DNA?
cAMP
How does the lac repressor block transcription?
Binds to O₁ and O₃, forming a DNA loop
