GAT-B Practice Quiz

Question 1

In the lac operon of Escherichia coli, which event most directly causes transcription to increase when lactose becomes available in the medium?

Accepted Answer

Allolactose binds the LacI repressor, reducing its binding to the operator

Question 2

Which statement best describes the trp operon when intracellular tryptophan levels are high?

Accepted Answer

Tryptophan acts as a corepressor and enables the repressor to bind the operator

Question 3

In a merodiploid E. coli strain with genotype lacI- O+ Z+ / lacI+ O+ Z-, what will be the effect of the lacI+ allele on regulation of the Z+ gene copy?

Accepted Answer

It will restore inducible regulation because LacI protein acts in trans

Question 4

A mutation in the trp leader peptide removes the two adjacent Trp codons but leaves the attenuator region otherwise intact. What is the most likely regulatory consequence?

Accepted Answer

The ribosome will no longer sense tryptophan availability effectively, impairing attenuation control

Question 5

Why is the lac operon only weakly transcribed when lactose is present but glucose is also abundant?

Accepted Answer

High glucose lowers cAMP, reducing CAP-mediated activation of the promoter

GAT-B Mock Test

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