Prokaryotic Gene Regulation and The Operon

A set of vocabulary flashcards covering the structures, mechanisms, and specific examples of gene regulation in prokaryotes, including the lac and trp operons.

Constitutive expression

Also known as 'house-keeping' expression, it refers to genes that are always expressed.

Induced expression

Gene expression that occurs in response to an environmental signal.

Repressed expression

Gene expression that is shut off when an environmental signal is present.

Promoter strength

The factor that determines the amount of each constitutive protein produced.

Operator

A segment of DNA that functions as an off/on switch, controlling an operon.

Promoter

A specific nucleotide sequence where RNA polymerase binds to start transcription.

Regulatory gene

A nucleotide sequence that produces a repressor that can interact with the operator.

Structural genes

Genes within an operon that code for a polypeptide.

Trp operon

An operon containing the genes for the production of tryptophan; it is an example of a repressible operon.

Lac operon

An operon containing the genes for the metabolism of lactose; it is an example of an inducible operon.

Repressible operon

An operon, such as the trp operon, where the activation of the repressor causes transcription to shut down.

Repressible enzymes

Enzymes whose synthesis is inhibited by a metabolite, such as those in the tryptophan biosynthesis pathway.

Inducible operon

An operon that is usually in an 'off' state, where inactivation of the repressor by an inducer turns on transcription.

Inducible enzymes

Enzymes involved in an inducible system, such as those used in the metabolism of lactose.

$\beta$-Galactosidase

An enzyme that catalyzes the hydrolysis of lactose into glucose and galactose.

Allolactose

Rearranged lactose that acts as the inducer for the lac operon by binding to the repressor and making it let go of the operator.

Permease

An enzyme involved in lactose metabolism, encoded by the lacY gene.

Transacetylase

An enzyme involved in lactose metabolism, encoded by the lacA gene.

CAP (Catabolite Activator Protein)

A protein that, when bound to cAMP, attaches to DNA to help RNA polymerase bind to the promoter, resulting in high levels of transcription.

cAMP

A molecule produced when glucose levels are low that attaches to CAP, allowing it to bind to the CAP site.

Inducer

A specific small molecule that inactivates the repressor in an inducible operon.

Corepressor

A small molecule that cooperates with a repressor protein to switch an operon off (e.g., tryptophan in the trp operon).