If there is a mutation in the operator of the lac operon such that lacI protein cannot bind the operator, will transcription of the lac operon occur?
Answer
a.
Yes, but only when lactose is present.
b.
No, because RNA polymerase can’t bind the promoter.
c.
Yes, since the operator will not be bound by repressor, RNA polymerase can bind the promoter.
d.
No, because cAMP levels are low when the repressor is nonfunctional.

Question

If there is a mutation in the operator of the lac operon such that lacI protein cannot bind the operator, will transcription of the lac operon occur?
Answer
	 a.	
 Yes, but only when lactose is present.
	 b.	
 No, because RNA polymerase can’t bind the promoter.
	 c.	
 Yes, since the operator will not be bound by repressor, RNA polymerase can bind the promoter.
	 d.	
 No, because cAMP levels are low when the repressor is nonfunctional.

alphadxg · Answer

Question is worded funny I have a guess, want to see what you guys think first.

anonymous · Answer

I believe it is B

alphadxg · Answer

hmm well if Lac operon is normally off, in the presence of lactose it is turned on to controll the amount of lactose present. so even if the repressor can't bind to the operator, doesn't mean it will not synthesize the genes coded for lactose. 

@sunshao1

anonymous · Answer

@Abhisar to the rescue

abhisar · Answer

Sorry guys !
No idea..studied this long time ago 
$\color{green}{\huge\ddot\frown}$

anonymous · Answer

ok I opened my molecular bio of the gene book HOLD ON

alphadxg · Answer

@sunshao1 ok, also remember cAMP and CAP are also determining factor as well, question is confusing overall.

anonymous · Answer

Yes the fact that CAP is there or not affects the level of expression

anonymous · Answer

OK
So the Lac repressor is encoded by the LacI gene

Since there is a  mutation in the lac operon such that it cannot recognize the expression of the LacI gene that must mean there is no repressor protein binded to the lac operon itself

anonymous · Answer

:'C

alphadxg · Answer

@sunshao1 wouldn't answer be A? Because if the repressor can't connect to the operator, then that means that the Operon is always turned on, and will always synthesize lactose genes, as long as their is lactose present? Wouldn't that make sense?

anonymous · Answer

ye I was getting to that but I got Dc'd. Ye I believe that it would be A then, but it all depends if glucose is present or not to determine CAP activity

alphadxg · Answer

@sunshao1 actually even if glucose is present or not, there will be small bits of transcription that will take place, looking at this question it gave us. Hopefully its the right answer, difficult question to understand, she worded it poorly.

shrutipande9 · Answer

i have come up with an explanation...gimme a min

anonymous · Answer

yes but it would be a basal metabolism with glucose present. which isn't much at all when compared to the full activated state

alphadxg · Answer

@shrutipande9 YES!! :)

shrutipande9 · Answer

see basically lacl is a repressor protein..so if it binds to the operator it would stop the function of lac gene which is responsible for breakdown of lactose. now mutation in operator so the repressor cannot bind. so lac operon is switched on continuously. but if lactose is not present it then it doesnt have a substrate to work on...

alphadxg · Answer

So, A would be the answer like I explained? @shrutipande9

shrutipande9 · Answer

sorry i explained halfway....d question asks transcription....so lets consider a case where lactose is not present. so normally d gene shouldd be switched off..so that not the case...RNA polymerase still binds and transcription occurs. so presence of lactose would not affect d transcription

alphadxg · Answer

@shrutipande9 So C?

shrutipande9 · Answer

yeah i think so

alphadxg · Answer

Thanks a lot for the help.

@shrutipande9 :)

shrutipande9 · Answer

^_^