Ox phospohorylation Flashcards
In ATP synthase, the interaction of stalk with a beta-subunit in the F1 complex contributes to ATP synthesis by:
Increasing the free energy of ATP dissociation from the beta subunit
Decreasing the free energy for formation of a phosphodiester bond between ADP and Pi
Decreasing the free energy of ATP dissociation from the beta subunit
Allowing the c-ring to rotate with a free energy of ~0
Increasing the free energy for protons to cross the membrane
Decreasing the free energy of ATP dissociation from the beta subunit
What is the P/O ratio for mitochondrial oxidation using NADH? (It indicates the number of ATP molecules generated per atom of oxygen consumed during the process)
3
2
1.5/2/.5
3/2
2.5
2.5
During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to:
create a pore in the inner mitochondrial membrane.
induce a conformational change in the ATP synthase.
generate the substrates (ADP and Pi) for the ATP synthase.
oxidize NADH to NAD+.
reduce O2 to H2O.
induce a conformational change in the ATP synthase.
For the following two half reactions:
Cytochrome c (Fe3+) + e– LaTeX: \rightarrow cytochrome c (Fe2+) E’ (V) = 0.220
FAD + 2H+ + 2e– LaTeX: \rightarrow FADH2 E’ (V) = -0.219
We would expect the spontaneous complete reaction to be:
Cytochrome c (Fe3+) + FAD + 2H+ -> cytochrome c (Fe2+) + FADH2
Cytochrome c (Fe3+) + FADH2 -> cytochrome c (Fe2+) + FAD + 2H+
2 cytochrome c (Fe2+) + FAD + 2H+ -> 2 Cytochrome c (Fe3+) + FADH2
2 Cytochrome c (Fe3+) + FADH2 -> 2 cytochrome c (Fe2+) + FAD + 2H+
2 Cytochrome c (Fe3+) + FAD + 2H+ -> 2 cytochrome c (Fe2+) + FADH2
2 Cytochrome c (Fe3+) + FADH2 -> 2 cytochrome c (Fe2+) + FAD + 2H+
When the ΔG’° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it is found to be close to zero. This is thought to be due to:
stabilization of ADP relative to ATP by enzyme binding.
stabilization of ATP relative to ADP by enzyme binding
enzyme-induced oxygen exchange.
None of the above
a very low energy of activation.
stabilization of ATP relative to ADP by enzyme binding.!
What is the final electron acceptor in Oxidative Phosphorylation?
Carbon dioxide
Water
Cytochrome c
Hydrides
Molecular oxygen
Molecular oxygen
Succinate dehydrogenase is dysfunctional in a species of garden slug. While its metabolism is compromised on a number of levels, it can still undergo oxidative phosphorylation. What is the maximal P/O ratio for these organisms if NADH is used as an electron source?
4
1.5
2.5
2
1
2.5
If succinate dehydrogenase is dysfunctional, it implies that the electron transport pathway involving FADH2 is compromised, but the pathway using NADH is still functional. As NADH feeds electrons into the electron transport chain at Complex I, you need to consider only the P/O ratio for NADH.
The P/O ratio for NADH is typically around 2.5, as discussed previously. This means that for every molecule of NADH oxidized, about 2.5 molecules of ATP are produced.
So, the maximal P/O ratio for these organisms using NADH as the electron source is:
2.5
How many reducing equivalents are transferred to molecular oxygen for the ten protons pumped out of the inner mitochondrial membrane by Complexes I through IV?
2
4
10
6
1
2
In the electron transport chain:
Complex I (NADH: ubiquinone oxidoreductase) pumps 4 protons into the intermembrane space per pair of electrons transferred.
Complex III (cytochrome bc1 complex) pumps 4 protons per pair of electrons transferred.
Complex IV (cytochrome c oxidase) pumps 2 protons per pair of electrons transferred.
When NADH is oxidized, it donates 2 electrons (a pair of electrons) to the electron transport chain, leading to protons being pumped by these complexes:
Complex I pumps 4 protons per 2 electrons.
Complex III pumps 4 protons per 2 electrons.
Complex IV pumps 2 protons per 2 electrons.
Thus, the total protons pumped by the electron transport chain per pair of electrons (2 electrons) is:
4 (Complex I) + 4 (Complex III) + 2 (Complex IV) = 10 protons
So, 2 reducing equivalents (represented by 2 electrons from NADH) are responsible for pumping 10 protons.
I add an inhibitor of mitochondrial respiration that prevents electron transfer to cytochrome c. Which of the following outcomes is the most likely?
Buildup of QH2 but not NADH; decreased oxygen consumption
Normal levels of QH2 and NADH; decreased oxygen consumption
Buildup of both QH2 and NADH; decreased oxygen consumption
Normal levels of QH2 and NADH; increased oxygen consumption
Buildup of QH2 but not NADH, increased oxygen consumption
Buildup of both QH2 and NADH; decreased oxygen consumption
An inhibitor that prevents electron transfer to cytochrome c would affect Complex III in the electron transport chain (ETC). Cytochrome c is the protein that transfers electrons from Complex III (cytochrome bc1 complex) to Complex IV (cytochrome c oxidase). If this transfer is inhibited, the following effects are expected:
Buildup of QH2 (ubiquinol):
Ubiquinol (QH2) carries electrons from Complex I and II to Complex III. If Complex III cannot transfer electrons to cytochrome c, QH2 will accumulate because it cannot pass its electrons to Complex III.
Buildup of NADH:
NADH is oxidized by Complex I, passing electrons to ubiquinone (Q), forming QH2. If QH2 accumulates and the electron transport chain is blocked at Complex III, NADH will also accumulate because its oxidation is also impeded.
Decreased oxygen consumption:
Oxygen serves as the final electron acceptor in the electron transport chain at Complex IV. If electrons cannot reach Complex IV (due to the block at Complex III), the consumption of oxygen will decrease substantially because the entire chain is stalled.
Given these points, the most likely outcome when an inhibitor prevents electron transfer to cytochrome c is:
Buildup of both QH2 and NADH; decreased oxygen consumption
Reactions catalyzed by which of the following proteins do NOT contribute electron carriers to the electron transport chain?
Alcohol dehydrogenase
Glucose-6-phosphate dehydrogenase
Malate dehydrogenase
Succinate dehydrogenase
Glucose-6-phosphate dehydrogenase
Alcohol dehydrogenase:
This enzyme catalyzes the oxidation of alcohols to aldehydes or ketones, producing NADH in the process. NADH is a direct electron carrier contributing to the electron transport chain (ETC).
Glucose-6-phosphate dehydrogenase:
This enzyme operates in the pentose phosphate pathway (PPP), catalyzing the first step and producing NADPH, not NADH. NADPH is primarily used in anabolic processes and in combating oxidative stress, but it does not feed electrons directly into the ETC.
Malate dehydrogenase:
This enzyme catalyzes the conversion of malate to oxaloacetate in the citric acid cycle, producing NADH, which then contributes electrons to the ETC.
Succinate dehydrogenase:
This enzyme is part of both the citric acid cycle and the electron transport chain (Complex II). It catalyzes the oxidation of succinate to fumarate and generates FADH2, which contributes electrons directly to the ETC.
Given this analysis, the enzyme whose catalyzed reactions do not contribute electron carriers directly to the electron transport chain is:
Glucose-6-phosphate dehydrogenase
