Lac operon

[Miracoli]

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Lac operon of E.coli is an example of
a) negative feedback regulation
b) positive feedback regulation
c) both
Please explain

 

[Mad Jack]

The lac operon can demonstrate both positive and negative feedback. It's kind of hard to explain, so here you go:

http://www.dnalc.org/view/15884-The-lac-operon.html

 

[seminoma]

Lac operon of E.coli is an example of
a) negative feedback regulation
b) positive feedback regulation
c) both
Please explain

I don't think it's negative or positive (or both), but gun to my head I would say positive feedback. Lac operon is considered a negative inducible operon, which means that it requires an inducer (allolactose) to repress its repressor. Positive feedback because the more allolactose around the more functional lac operons will be. Since its purpose is to metabolize lactose and in the presence of lactose it is active, that sounds more like positive feedback to me.

The only "negative" feedback involved is with glucose, but glucose doesn't actually inhibit the operon. Glucose inhibits transport of lactose into the cell. So really, it's not a negative feedback on the operon itself, but rather the ecoli as a whole.

 

[Miracoli]

Those 2 sources say that it is both.
http://www.ncbi.nlm.nih.gov/books/NBK22091/

https://books.google.com/books?id=C...egative control and positive control.&f=false