Question

If you introduced a strongly expressed gene for a mutant enzyme that constitutively exhibited adenylate cyclase activity, what would you predict to be the relative level (high/normal/low) of β-galactosidase activity in the following growth conditions? Explain each answer.

1. Presence of both glucose and lactose (3 points)

2. Absence of glucose, presence of lactose (3 points)

           

3. Absence of glucose and absence of lactose (3 points)

Answer 1

A) presence of glucose and lactose cause decrease in conc.of cAMP and hence CAP- cAMP complex cannot form and cannot bind to promotor.So RNA polymerase enzyme cannot do transcription and hence lac operon will be switch off even if lacose is present.

So beta glactosidase enzyme cannot synthesis.

B) Absence of glucose and presence of lactose only cause switch on condition of lac operon.

As absence of glucose cause accumulation of cAMP and hence cAMP-CAP protein become active and bind to promotor and hence RNA polymerase cause continous mRNA synthesis.

beta glactosidase enzyme form.

C) absence of glucose and absence of lactose cause switch off of lactose operon so no beta glactosidase enzyme form.

Here absence of glucose cause synthesis of cAMP and cAMP- CAP protein complex also goes that hold TNA pol to continous transcription but operator is occupied by lac repressor which will not allow RNA polymerase to cause transcription and hence lac operon switch off.

Hope it's clear..thanks