[Campbell Biology P.210] Which of the following statements accurately describes the mechanis... | Practice Question

Which of the following statements accurately describes the mechanism of feedback inhibition in isoleucine synthesis as shown in Figure 8.21?

  • A: Threonine binds to the allosteric site of Enzyme 1, activating it and speeding up isoleucine production.
  • B: The end product, isoleucine, binds to the active site of Enzyme 5, deactivating it and stopping the pathway.
  • C: Isoleucine accumulates and binds to the allosteric site of Enzyme 1, preventing its active site from catalyzing the conversion of threonine to Intermediate A.
  • D: Intermediate D acts as an inhibitor, binding to Enzyme 4 and halting the pathway by competitive inhibition.

Explanation

Feedback inhibition is described as the end product of a pathway binding to an enzyme early in the pathway to halt its own synthesis. Figure 8.21 specifically shows isoleucine, the end product, binding to an allosteric site on Enzyme 1 threonine deaminase , which prevents its active site from functioning, thereby stopping the conversion of threonine to Intermediate A and halting the entire pathway.