Exam 5 - Lac Operon Flashcards
(15 cards)
Lac Operon in Bacteria
a genetic regulatory system that controls the metabolism of lactose by regulating the expression of genes involved in lactose transport and digestion, depending on the presence or absence of lactose.
Lactose Metabolism
In prokaryotes, gene activity is repressed when lactose is absent and induced when available
In the presence of lactose, the concentration of enzymes responsible for its metabolism increases = inducible enzymes
Inducible enzymes
Bacteria adapt to environment by producing inducible enzymes only when specific substrates are present
Constitutive enzymes
Enzymes are continuously produced regardless of chemical makeup of environment
b-galactosidase
an inducible enzyme that breaks the bond between galactose and glucose
Promotor
a region of DNA located upstream of a gene that serves as the binding site for RNA polymerase and other transcription factors, initiating the process of transcription to produce RNA from the gene.
Operon
a group of genes in bacteria that are controlled and regulated together by a single promoter and operator, allowing the coordinated expression of genes involved in a specific metabolic pathway or process
Operator
a segment of DNA within an operon that acts as a binding site for regulatory proteins, such as repressors, which can inhibit or promote the transcription of the genes in the operon depending on the presence of specific signals (like metabolites)
Positive control of Gene Expression
Transcription occurs only when regulator molecule directly stimulates R N A production
May can induce or repress systems
Negative control of Gene Expression
Genetic expression occurs unless shut off by regulator molecule
May can induce or repress systems
CAP: Catabolite-activating protein
Exerts positive control over lac operon
Diminishes expression of operon when glucose is present (catabolite repression)
Binds to CAP-binding site, facilitating RNA polymerase binding at promoter and facilitating transcription
cAMP: Cyclic adenosine monophosphate
Binds to CAP allowing it to bind to the promotor
Glucose inhibits activity of adenylyl cyclase, which catalyzes conversion of ATP to cAMP
Prevents CAP from binding when glucose is present
No glucose
No lactose
Impact in different regions for lactose breakdown
Wild type —
Lac operon promotor —
Operator site +++
lacA gene —
CAP site —
Glucose
Lactose
Impact in different regions for lactose breakdown
Wild type +
Lac operon promotor —
Operator site +
lacA gene +
CAP site +
No glucose
Lactose
Impact in different regions for lactose breakdown
Wild type +++
Lac operon promotor -
Operator site +++
lacA gene +++
CAP site +
