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Biology 1002B Chapter Notes - Chapter 4.4: Nadh Dehydrogenase, Cytochrome C Oxidase, Oxidative Phosphorylation

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School
Western University
Department
Biology
Course
Biology 1002B
Professor
Tom Haffie Denis Maxwell

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Oxidative Phosphorylation: Electron Transport and Chemiosmosis
• Potential energy in glucose now exist as ATP, NADH, and FADH2
• ETC and chemiosmosis use NADH and FADH2 to synthesize even more ATP
6.5a Electron Transport Chain
• Consists of 4 protein complexes: NADH dehydrogenase (complex I), succinate
dehydrogenase (complex II), cytochrome complex (complex III), cytochrome oxidase
(complex IV)
• Complex II is a single peripheral membrane protein, others are composed of multiple
proteins
• Major complexes are I, III, and IV
• Complex II passes e- to UQ
• UQ (ubiquinone) is a hydrophobic molecule found in core of membrane and shuttles e-
from complexes I and II to complex III
• Cytochrome c (cyt c) is located on intermembrane space side of membrane and transfers
e- from complex III to complex IV
• Complexes I and IV pump H+ into intermembrane space
6.5b Electrons Move Spontaneously Along the Electron Transport Chain
• Proteins do not transfer e-, non-protein molecules called prosthetic groups accept e- from
upstream and donate e- to downstream molecules
• One of the prosthetic groups of complex I, FMN, is reduced by NADH from matrix side of
inner membrane
• FMN donates e- to Fe/S prosthetic group, which donates e- to UQ
• E- is transported along chain until e- are donated to O2, which reduces it to water
• What is the driving force of e- transport?
o Prosthetic groups are organized from high to low free energy
o NADH has high potential energy and can be readily oxidized
o O2 at the end of the chain is strongly electronegative and can be easily reduced
o This organization means e- movement is thermodynamically spontaneous
6.5c Chemiosmosis Powers ATP Synthesis by a Proton Gradient
• Energy released during e- transport moves H+ from matrix to intermembrane space
• H+ concentration becomes higher and the pH lower in intermembrane space than matrix
• Complexes I and IV pump H+
• UQ that accept e- from complex I or II also pick up H+ and release H+ into intermembrane
space after donating e- to maintain neutral charge
• Proton-motive force: stored energy that contributes to ATP synthesis
o Chemical gradient - proton is not equal on both sides
o Electrical difference - intermembrane space more positively charged than matrix
• Chemiosmosis: ability of cells to use proton-motive force to do work
• Oxidative phosphorylation: synthesis of ATP using H+ gradient and ATP synthase
6.5e Electron Transport and Chemiosmosis Can Be Uncoupled
• E- transport and chemiosmosis to generate ATP are separated processes
o Possible to have high rates of e- transport (thus high rates of O2 consumption) but
not ATP generated by chemiosmosis
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Related Questions

15. The prosthetic group of NADH dehydrogenase:

A. FMN

B. NADH

C. FAD

D. NADPH

E. Iron

16. What type of reactions form the basis of the electron transport chain and what is the final electron acceptor?

A. Acid-base reactions; O2

B. Acid-base reactions; water

C. Oxidation-reduction reactions; water

D. Oxidation-reduction reactions; NADH

E. Oxidation-reduction reactions; O2

17. Which shows the proper order of electron transfer for the listed electron transport chain components (not all electron carriers are shown)?

A. NADH → → Q → → cytochrome c → → O2

B. O2 → → cytochrome c → → Q → → NADH

C. NADH → → cytochrome c → → Q → → O2

D. Q → → NADH → → cytochrome c → → O2

E. NADH → → O2 → → cytochrome c → → Q

18. Which complex oxidize NADH and FADH2 respectively in the electron transport chain

A. Complex I, Complex I

B. Complex I, Complex II

C. Complex II, Complex III

D. Complex II, Complex I

E. Complex II, Complex IV

19. Which of the following is a component of Succinate dehydrogenase in Electron transport chain?

A. Niacin

B. FMN

C. FAD

D. Coenzyme Q

E. Lipoic acid

20. In electron transport the flow of electrons:

A. is bidirectional

B. goes from a high energy state to a low energy state

C. takes place in the outer mitochondrial membrane

D. are used to pump H+ into the mitochondrial matrix

21. Which of the following statements about the electron transport chain is NOT correct

A. It is located in the inner mitochondrion membrane

B. Cytochrome c accepts electrons from complex II

C. Cytochrome c oxidase (complex IV) accepts electrons from Cytochrome c

D. Complex I is called NADH dehydrogenase

E. Coenzyme Q accepts electrons from complex I and complex II

22. In the electron transport chain, the enzyme cytochrome C oxidase:

A. Uses H2O as a substrate

B. Produces HOOH as a product

C. Cannot function if oxygen is absent

D. Accepts electrons from hydrogen ions

E. Uses ADP and Pi as substrates

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 “electrons flow down the electron-transport chain”?

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.