Question

I-P+O+Z-Y+/I-P+O+Z+Y-

I+P+O+Z-Y+/ISP+O+Z+Y-

Is Lactose Absent/Present for Lac Y/Z? Glucose is present.

-: no

+: transcription

++: Intense transcription

Answer 1

I-P+O+Z-Y+/I-P+O+Z+Y-

I+P+O+Z-Y+/ISP+O+Z+Y-

Lac I protein is the repressor protein that binds to the operator region(O) of the promoter (P) and prevent RNA polymerase from binding to the promoter sequence and transcribing the lac operon structural genes (Z for beta galactosidase,Y for lactose permease) which are required for lactose metabolism.

So when lactose is present it will bind to the repressor protein (in the form of allolactose) there by preventing it from binding to the operator sequence there by enabling the RNA polymerase to start the transcription of lac operon genes.

I-P+O+Z-Y+/I-P+O+Z+Y-

Here lac I repressor (I) is not present (I--), promoter P is present (P++), operator is present (O++) ,lac Z is present (Z-+), lac Y is present (Y+-)

So here since there is no repressor there will be transcription of lac Z and lac Y even when there is no lactose present.SO there will be transcription in the presence and absence of lactose.

Even when glucose is present (or absent) there will be transcription since there is no repressor to switch off lac operon in the presence or glucose