Question

what would happen to the 3rd stage of respiration if we add a "drug" that takes electrons away from NADH or FADH2 and stores/holds onto electrons permanently?

Answer 1

Electron transport chain (ETC) is third stage of cellular respiration, the firsts two stages being glycolysis and Krebs cycle. There are four complexes in ETC: 1-IV. Complex I accept electrons from NADH2 and donates it to coenzyme Q or complex II. FADH2 donates its electrons to complex II and is converted to FAD+. The electrons in complex II are accepted by complex III and then to complex IV via cytochrome c. This creates a proton gradient due to transport of H+ from matrix. The electron transport causes loss of energy from electrons, which is used for transport of H+ ions. This leads to generation of an electrochemical gradient, which is used by ATP synthase enzyme to form ATP. ATP synthase transport H+ ions back to matrix. The electrons are accepted by oxygen to form water.

If the drug inhibits takes away electrons from NADH2 and FADH2, then electrons cannot be transported by the ETC. This will inhibit oxidative phosphorylation. There is inhibition of ATP synthesis as ATP synthase cannot convert ADP and Pi to ATP. Thus, the cell will have no ATP for cellular activities and will die.