Concept #1: Positive Feedback

Practice: The reaction Fructose-6-P + ATP <===> ADP + Fructose-1,6-bisP is catalyzed by the glycolytic enzyme phosphofructokinase-1 (PFK-1). In muscle tissue, PFK-1 is a homotetramer (contains 4 identical subunits). Adenosine monophosphate (AMP) binds at a site distant from the site of catalysis on any of the four subunits & induce a conformational change that favors a relaxed & more active state of the whole tetramer. How is the role of AMP classified in this reaction?

Concept #2: Metabolic Pathway Communication

Practice: Use the image below showing interactions between 3 metabolic pathways to answer the following questions.

A) Which of the following best describes the role of molecule “F”?

a) At low concentrations, molecule F acts as an inhibitor on enzyme-1 & an activator on enzyme-6.
b) At high concentrations, molecule F acts as an activator on enzyme-1 & an inhibitor on enzyme-6.
c) At low concentrations, molecule F acts as an activator on enzyme-1 & an inhibitor on enzyme-6.
d) At high concentrations, molecule F acts as an inhibitor on enzyme-1 & an activator on enzyme-6.

B) Which of the following best describes the role of molecule “I”?

a) At high concentrations, molecule I acts as an inhibitor on enzyme-6 & an activator on enzyme-1.
b) At low concentrations, molecule I acts as an activator on enzyme-6 & an inhibitor on enzyme-1.
c) At high concentrations, molecule I acts as an activator on enzyme-6 & an inhibitor on enzyme-1.
d) At low concentrations, molecule I acts as an inhibitor on enzyme-6 & an activator on enzyme-1.


C) Which of the following best describes the role of molecule “K”?

a) At low concentrations, molecule K acts as an inhibitor on enzyme-1 & an activator on enzyme-6.
b) At high concentrations, molecule K acts as an inhibitor on enzyme-1 & an inhibitor on enzyme-6.
c) At low concentrations, molecule K acts as an activator on enzyme-1 & an inhibitor on enzyme-6.
d) At high concentrations, molecule K acts as an inhibitor on enzyme-1 & an activator on enzyme-6.