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9.1 Bacterial Operons & Gene Regulation β Test 1
Q1. The true inducer of the lac operon is:β Allolactose
Q2. The prevention of lac-operon induction by excess glucose is known as:β Catabolite repression
Q3. In bacteria, catabolite repression conserves energy by:β Regulating genes for use of less-efficient (alternative) carbon sources
Q4. A mutation in the lac operator (lacO^c) results in:β Constitutive expression
Q5. An E. coli mutant with a non-functional LacI repressor will show:β Constitutive expression of Ξ²-galactosidase
Q6. In a merodiploid analysis, strain P1 is O^c I^+ Z^-, strain P2 is O^+ I^- Z^+, and D is the merodiploid. The pattern of Z (Ξ²-galactosidase) expression is:β P1 none, P2 constitutive, D inducible
Q7. An E. coli culture grows on glucose + lactose. When glucose is depleted, Ξ²-galactosidase expression will:β Increase
Q8. In the trp operon, tryptophan regulates transcription by:β Binding the repressor, which then binds the operator to block transcription
Q9. The lac operon is an example of which type of regulatory system?β Negative inducible
Q10. The trp operon is an example of which type of regulatory system?β Negative repressible
Q11. Positive control of the lac operon is mediated by:β CAP (catabolite activator protein) bound to cAMP
Q12. IPTG is widely used in the laboratory as a lac inducer because it is:β A gratuitous (non-metabolisable) inducer
Q13. An operon is best defined as:β A cluster of genes transcribed from one promoter as a polycistronic mRNA
Q14. The operator of an operon is a:β Cis-acting DNA sequence where the repressor binds
Q15. The operon model of gene regulation was proposed by:β Jacob and Monod
Q16. Attenuation of the trp operon depends on:β The level of charged tryptophanyl-tRNA controlling a leader-peptide stall
Q17. Inducible operons (like lac) and repressible operons (like trp) typically control, respectively:β Catabolic and anabolic pathways
Q18. The lac repressor, in the absence of inducer, binds to the:β Operator, blocking RNA polymerase progression
Q19. A bacterial mRNA that encodes several proteins from one transcript is described as:β Polycistronic
Q20. Match each lac-operon element with its property and select the correct option.β A-ii, B-i, C-iv, D-iii