Question

6. Which of the following would you expect to result from a block of electron transfer at complex II. Check all correct answers and explain.

a. Reduction in oxidative phosphorylation

b. No change in the proton gradient across the inner mitochondrial membrane

c. FADH2 accumulation

d. Damage to the cells due to reactive oxygen species accumulation

Explanation:

Answer 1

Complex II of the ETC (Electron Transport Chain) is the Succinate Reductase of the Citric Acid Cycle. This enzyme converts Succinate to Fumarate. In this process, electrons are extracted. These electrons are captured by the electron transporter FAD, thereby resulting in the formation of FADH2.

FADH2 donates electrons to the ETC and is thereby converted back to FAD. The electrons are then transported down the ETC to Complex III and Complex IV resulting in the expulsion of H+ ions outside the membrane. Thus, a concentration gradient is generated that will then drive the ATP Synthase.

Thus, the blockage of Complex II will result in the accumulation of FADH2 in the cell as the electrons cannot be donated by this carrier to ETC. Also, the reduction of electrons in the ETC will result in the proton gradient being affected. This proton gradient is essential for the ATP Synthase to function. Hence, ATP synthesis also called oxidative phosphorylation will decrease. However, this will not impact the reactive oxygen species in the cell as enough electrons will still be pumped in for O2 to react with it.

Thus, the correct options are a and c.