How does a high concentration of adenosine triphosphate together with low adenosine diphosphate affect phosphofructokinase?
AThe enzyme changes its substrate
BThe enzyme becomes more active
CThe enzyme becomes less active
DThe enzyme is destroyed completely
Answer & Solution
Correct answer: C. The enzyme becomes less active
1. Phosphofructokinase is active when the concentration of adenosine diphosphate is high.
2. It is less active when adenosine diphosphate levels are low and adenosine triphosphate is high.
3. High adenosine triphosphate signals that the cell already has enough energy, so the pathway slows down.
4. This is a type of end product inhibition, since adenosine triphosphate is the end product of glucose catabolism.
5. The enzyme is only slowed, not destroyed, so it can speed up again when demand returns.
6. Its substrate never changes, because inhibition alters activity rather than specificity.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.2 Glycolysis_
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