What is feedback inhibition in metabolic regulation?

• A. The product inhibits earlier steps in its own biosynthetic pathway.
• B. It increases the rate of all steps in the pathway.
• C. It occurs only in eukaryotes.
• D. It is a form of competitive inhibition at the active site.

Answer: (A)

Feedback inhibition is a negative feedback mechanism where the end product of a pathway binds to and inhibits an enzyme early in that pathway, preventing unnecessary overproduction and conserving resources. This control keeps the flux of metabolites aligned with the cell’s needs. The end product typically binds at an allosteric site, causing a conformational change that reduces enzyme activity, rather than competing with the substrate at the active site. This distinction explains why feedback inhibition is often allosteric rather than strictly competitive. It also isn’t limited to eukaryotes; many bacteria and other organisms use this form of regulation. A classic example is isoleucine inhibiting the first enzyme in its own biosynthetic pathway, threonine deaminase, when isoleucine levels are high.