BIOCHEM 2EE3 Lecture Notes - Cytochrome C, Reduced Form, Mitochondrial Matrix

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11 Mar 2014

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The other electron goes to cytochrome b in complex three. Four cytochrome c"s to reduce oxygen to water: protons are involved in electrochemical gradient which is needed for synthesis of atp. Total of 10 protons: explains how pumping of electrons allows for synthesis of atp. If you increase permeability of mitochondrial membrane to allow for passage of ions to go through, this blocks atp synthesis: need electrochemical gradient to power atp synthesis, pumps protons from matrix to intermembrane space, chemiosmotic theory explains. If you increase cytosolic concentration of h ions, increases h concentration across intermembrane space, increases atp production (?) Three protons must be moved to allow atp synthesis: composed of five sub-units. F1 in matrix: alpha sub-units red, beta sub-units yellow, gamma sub-units blue, bottom of gamma tethered to fo component by epsilon and delta, which are not seen in this structure. This is e. coli, not mitochondrial atp synthase: figure out the differences.

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Can you answer the following questions:

1. Carbon monoxide is considered toxic because it acts on Complex IV. How would the addition of carbon monoxide to actively respiring mitochondria affect the relative oxidation-reduction states of all components of the electron-transport chain?

A) All four complexes would remain oxidized because they function as a multisystem complex.

B) Complexes I and III would be reduced, but complexes II and IV would be oxidized because the

electrons come from FADH2 oxidation, not NADH.

C) Complexes I, II, and III would be oxidized but Complex IV would remain reduced.

D) Complexes I, II, and III would be reduced and Complex IV would be oxidized.

E) All four complexes would remain reduced because they function as a multisystem complex.

2. Electrons are not very soluble in hydrophobic environments such as a bilipid membrane. What evidence is there that electrons move from complex to complex through the lipid membrane?

A) Cytochrome C is the electron carrier in the membrane and undergoes a head-over-heel flip to set up the proton gradient.

B) Cytochrome C is the electron carrier in the membrane and contains a cydrophoric porphyrin center.

C) CoQ is the electron carrier within the membrane and seems to be confined to the respirasome.

D) CoQ is the electron carrier within the membrane and it contains a hydrophobic porphyrin center.

E) FeS clusters are the carriers within the membrane and the electrons move from one cluster to the

next in a chain-like fashion.

3. What is the rationale for saying that âelectrons flow down the electron-transport chainâ?

A) Electrons flow from oxidized carriers to reduced carriers in discrete steps like a staircase.

B) Electrons flow from half-reactions with more positive redox potentials to more negative.

C) Electrons flow from reactions that continuously generate negative free energy values.

D) Electrons flow from the outer surface to the inner surface, a top down perception.

E) Because we think of electrons flowing like a liquid, the only direction electrons can flow is down.

1. Compared to the generation of ATP by oxidative phosphorylation, what is a major difference in mechanism of ATP generation by substrate-level phosphorylation in glycolysis?

A. A proton gradient is not involved

B. The ATP produced has less energy content because oxygen was not involved.

C. Substrate level phosphorylation occurs in the inter-mitochondrial space

D. One can't generalize without knowing the substrate.

2. Which of the following statements is true?

A. Because the electrons in NADH are at a higher energy than the electrons in reduced ubiquinone, the NADH dehydrogenase complex can pump more protons than can the cytochrome b-c1 complex.

B.The pH in the mitochondrial matrix is higher than the pH in the intermembrane space.

C. The proton concentration gradient and the membrane potential across the inner mitochondrial membrane tend to work against each other in driving protons from the intermembrane space into the matrix.

D. The difference in proton concentration across the inner mitochondrial membrane has a much larger effect than the membrane potential on the total proton-motive force.

Which of the following is a substrate or component of complex IV:

a. FMN

b. CuB

c. oxidized cytochrome c

d. Fe-S protein.

F₀F₁ ATP synthase:

a. has a c-ring that can only be made of 8-subunits

b. requires 12 protons to make 3 ATP in all mammalian tissues.

c. converts an electrochemical gradient into mechanical energy to drive the removal of ATP from its active site.

d. None of the above.

Throughout the course we discussed the impact that the removal of oxygen would have on cellular metabolism during strenuous exercise and in this last unit applied it to mitochondrial metabolism. Given these discussions we can say that anaerobic conditions:

a. lead to the reduction of each complex in the electron transport chain

b. lead to the accumulation of NADH in the matrix of the mitochondria.

c. lead to a diminished activity of ATP synthase.

d. All of the above.

The addition of 2,4-dinitrophenol (DNP) to a suspension of mitochondria in which an inhibitor of ATP synthase is present along with the reduced electron carrier succinate will cause which of the following to occur?

a. Proton flow from the N to P-side via complex II.

b. The concentration of NADH to increase in the matrix due to subsequent inhibition of the electron transport chain.

c. Increased rate of oxygen reduction.

d. Decreased flux through complex III.

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BIOCHEM 2EE3 Lecture Notes - Cytochrome C, Reduced Form, Mitochondrial Matrix

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