Problem 10 - Entrance Test

Cyanide blocks the transfer of electrons from cytochrome c oxidase to oxygen, effectively shutting down the electron transport chain. This prevents the regeneration of NAD+ and FAD from NADH and FADH2, leading to an accumulation of NADH and FADH2 in the mitochondrial matrix (as they cannot donate their electrons). Consequently, the proton gradient across the inner mitochondrial membrane collapses, halting ATP synthesis by chemiosmosis. While glycolysis might transiently increase as a compensatory mechanism, the primary and immediate effect is the backup of electron carriers. The pH in the intermembrane space would increase (become less acidic) due to the failure of proton pumping, not decrease. The Krebs cycle enzymes would not be directly inhibited, but their substrates would eventually accumulate due to the lack of regenerated NAD+ and FAD.