Feedback inhibition occurs when a pathway end product inhibits an earlier enzyme, preventing excess product accumulation through negative feedback in pathways.
Coverage 2012–2024 · Updated 15 Jul 2026
Feedback inhibition regulates a metabolic pathway when its end product reversibly inhibits an enzyme near the beginning of that pathway.
As end product accumulates, binding to a regulatory site lowers early-pathway activity and prevents unnecessary substrate and energy use. When product concentration falls, inhibition decreases and flux resumes.
In isoleucine synthesis, accumulated isoleucine inhibits an early enzyme in its own pathway. This negative-feedback loop matches production to demand without reversing the intervening reactions.
High isoleucine → early enzyme inhibited → fewer downstream intermediates → isoleucine production slows; use by the cell lowers isoleucine → inhibition eases → production increases.
The end product is a regulator, not a substrate for the inhibited step, and feedback inhibition controls pathway flux rather than proving that the pathway runs backwards.
This objective is assessed through structured response, commonly using Explain / Outline / State.
Explain / Outline / State
Build the answer around this relationship: End products can inhibit enzymes near the start of a pathway.
Representative question
Outline the control of metabolism by end-product inhibition.
Enzymes can act inside or outside cells, metabolic reactions release heat, pathways may be linear or cyclical, and pathway output is regulated by inhibition. Competitive inhibitors bind active sites and can be overcome by more substrate; non-competitive inhibitors bind allosteric sites; feedback inhibition uses end products to inhibit earlier enzymes; mechanism-based inhibitors trap enzymes after reaction begins.
