What is feedback inhibition in metabolic pathways?

• A. The first enzyme inhibits the last substrate.
• B. The last enzyme in a pathway is inhibited by the end-product of the pathway.
• C. All enzymes are inhibited equally by the product.
• D. The first enzyme is inhibited by the substrate.

Answer: (B)

Feedback inhibition is a regulatory mechanism where the end product of a pathway slows or stops the pathway by inhibiting an enzyme in that same pathway. In this case, the end product inhibits the last enzyme, which reduces the flux through the final step and prevents overproduction. This creates a negative feedback loop that helps maintain balanced levels of the product and conserves resources. The other ideas either describe atypical scenarios or ignore the idea that regulation is usually targeted to a specific step, not all enzymes or the substrate itself.