Practice question

Lac operon integrates two environmental signals via negative and positive inputs ensuring efficient carbon utilization hierarchy. Catabolite activation provides positive regulation: when glucose scarce, adenylate cyclase raises cyclic AMP concentration, enabling CRP-CAP dimer formation. CAP, also known as catabolite activator protein, binds upstream site at -61.5, introduces 90-degree DNA bending, and contacts alpha-carboxy-terminal domain of RNA polymerase, stabilizing binding and promoting isomerization to open complex and enhancing transcription roughly fifty-fold beyond basal derepressed level. LacI repressor causes negative inhibition blocking polymerase, IPTG acts as derepressor mimicking inducer allolactose, and beta-galactosidase is structural enzyme downstream of regulatory control mechanisms.