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Structural genes
Genes that code for the production of polypeptides, which can become proteins or part of functioning proteins, involved in structural or metabolic functions.
mRNA synthesis
The primary process involved in the expression of structural genes, although some are transcribed for tRNA/rRNA synthesis.
Regulatory genes
Genes that code for transcription-controlling proteins that can bind to DNA to regulate gene expression.
Repressor proteins
Proteins produced from regulatory genes that can bind to promoter regions or other DNA regions to control gene expression.
Repressible enzymes
Enzymes that are continuously produced and involved in anabolic pathways, with production rates decreasing in response to high product concentrations.
Allosteric sites
Specific sites on inactive repressor proteins where products can bind, activating the repressors to inhibit RNA polymerase binding.
Inducible enzymes
Enzymes that are produced only when the gene coding for them is activated in the presence of specific molecules.
Constitutive enzymes
Enzymes that are continuously produced, similar to repressible enzymes, but are always expressed.
Lac operon
A genetic system that includes three structural genes (lacZ, lacY, lacA) coding for enzymes involved in lactose metabolism and regulation.
lacZ
A structural gene in the lac operon that codes for beta-galactosidase, which hydrolyzes lactose.
lacY
A structural gene in the lac operon that codes for lactose permease, a membrane transport protein for lactose.
lacA
A structural gene in the lac operon that codes for transacetylase, involved in sugar metabolism and detoxification.
Operator
A DNA segment adjacent to structural genes in the lac operon that regulates their expression by turning them on or off.
Promoter
A DNA region adjacent to the operator where RNA polymerase binds to initiate mRNA formation from structural genes.
lacI regulatory gene
A gene that codes for a repressor protein that binds to the operator, preventing RNA polymerase from transcribing the lac genes by default.
