Shown above is a schematic of the electron transport chain (ETC) in a typical animal cell. NADH (not shown) donates electrons to Flavin mononucleotide (FMN), and FADH 2 donates electrons to an iron-sulfur complex (FeS), which donates them to ubiquinone (Q).
How does transfer of electrons from one carrier to another in the ETC generate a proton gradient across the inner mitochondrial membrane?
Electron transport along the transport chain is associated with a redistribution of charges in the mitochondrial membrane, resulting in excess or insufficient potential locally in certain areas. Protons tend to make up for the insufficient potential, so they will migrate to places of decreased charge or move away from places of increased charge.
There are poisons that can specifically block or hinder either FMN or the Fe-S in complex II that accepts electrons from FADH 2 . Which poison (against FMN, or against the Fe-S in complex II) will have a more detrimental effect on the proton gradient, and why?
FMNH2 poisoning is expected to have a more deleterious effect on the proton gradient because one of the primary chains of electron migration within the membrane is disrupted in this case. In addition, FMNH2 is involved in the release of protons involved in migration through ATP synthase, so disabling FMNH2 would result in the loss of this proton action to a greater extent.
Would the poisons described above increase oxygen consumption, decrease it, or have no effect? Explain.
Oxygen consumption occurs in one of the last phases, particularly in complex IV. The poisoning of any of the phases from the previous assignment will affect electron migration, rendering the action of complex IV ineffective. This will be realized as a cascade reaction in which the problem occurred long before the oxygen use site.
Which electrons have more energy—those accepted by Q, or those accepted by cytochrome c (Cyt c), and how do you know?
Q takes electrons (two pieces) from the first complex and two electrons from the second complex; the total is four. Cyt c takes only two electrons from the third complex. Therefore, we can assume that Q has cumulatively higher energy than Cyt c.
From which, and into which cell compartments are electrons pumped during electron transport in cell respiration?
Q receives electrons from FMNH2 and FAD(II) and gives them to QH2, after which they migrate to complex (III), whereas Cyt C receives electrons from complex III and gives them to complex IV.
What would be the effect on ATP production of decreasing the pH inside the mitochondrial matrix? Explain.
If the intramitochondrial matrix decreases its level of acidity, this will lead to a reduction in the number of free protons inside. As a result, the mitochondria will transfer large amounts of protons into the intermembrane space, leading to the formation of ATP.