Re: [HAPS-L] End-product inhibition

["John Cornell" <jccornell@xxxxxxxxx>]

Ken and all,
After further consideration I find that I am now happy with end-product inhibition as an example of negative feedback (the control system is found in the enzyme(s) I have decided).  The point that I was really trying to make, and not well, was that a feedback system (positive or negative) must have in its design a part where the output is fed back to a control center where the output strength becomes an input that is used to modify the output in the future. (If the output were not fed back [to a control center] then it wouldn't be a feedback system.) I think what Margaret was getting at is that it may be difficult to identify the elements of the control system (sensor, comparator/controller, set point generator, integrator etc.) which can be found in the feedback system--to which I certainly agree. I think it can be misleading to identify a feedback system only on the basis of the output, 
e.g., a chain reaction  behaves in a manner similar to audio feedback, but I do not consider chain reactions (e.g., nuclear bomb type) to be  positive feedback.  Biological examples that I usually give for positive feed back include childbirth, orgasm, defecation, and parts of fever generation.  I find that many students sometimes think that amplification alone is sufficient -- hence my mention of cascades. I know that I have not always been guilty of presenting the clearest explanation of these topics so please, everyone, what do you think?
John