Chapter 20 The Electron-Transport Chain
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) mitochondria
b) cytochrome c
c) coenzyme Q
d) FMN
e) iron-sulfur clusters
f) respiration
g) transporters
h) porins
i) succinate dehydrogenase
j) cytochrome c oxidase
k) Complex II
l) Complex III
1.
____________ This is where oxidative phosphorylation occurs in eukaryotes.
2.
____________ An ATP-generating process in which an inorganic substance such as oxygen
serves as the ultimate electron acceptor.
Section: Introduction
3.
____________ The permeability of the outer mitochondrial membrane is primarily due to the
presence of these substances.
Ans: h
4.
____________ This electron carrier is a derivative of quinone and has an isoprenoid tail.
5.
____________ This enzyme catalyzes the reduction of O2.
Ans: j
Ans: a
Chapter 20 The Electron-Transport Chain
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6.
____________ This prosthetic group is present in Complexes I, II, and III of electron
transport.
7.
____________ This citric acid cycle enzyme is also part of an electron-transport complex.
Ans: i
Section: 20.3
8.
____________ Prosthetic group in Complex I that accepts electrons from NADH.
Ans: d
Section: 20.3
9.
____________ The complex with three Fe-sulfhydryl electron acceptors.
Ans: k
Section: 20.2
10.
Ans: f
Section: Introduction
____________ This is a process by which cytoplasmic NADH can be oxidized by O2 using the
electron-transport system.
Fill–in-the-Blank Questions
11.
A strong oxidizing agent has a tendency to (accept, donate) electron(s).
Ans: accept Section: 20.1
12.
Another name for coenzyme Q is .
Ans: ubiquinone Section: 20.1
13.
Cytochrome is the only water-soluble cytochrome of the electron-transport chain.
Ans: c Section: 20.3
14.
Cytochrome c oxidase contains two heme A groups and three ions.
Ans: copper Section: 20.3
15.
carries electrons from Complex III to Complex IV.
Ans: Cytochrome c Section: 20.3
16.
The transfer of a single electron to O2 forms the reactive ion.
Ans: superoxide Section: 20.3
17.
donates electrons to cytochrome C.
Ans: Cytochrome C reductase complex Section: 20.3
Ans: e
Section: 20.2
Chapter 20 The Electron-Transport Chain
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18.
is an enzyme that scavenges H2O2 and converts it to molecular oxygen and water.
19.
Complex IV is also known as .
Ans: cytochrome c oxidase Section: 20.3
20.
are the result of uncontrolled electron transfer to oxygen
Ans: Oxygen radicals Section: 20.3
Multiple-Choice Questions
21.
Choose the correct path taken by a pair of electrons as they travel down the electron-transport
chain.
A)
NADH → Complex I → CoQ → Complex III → Cyt c → Complex IV → O2
B)
FADH2 → Complex I → CoQ → Complex III → Cyt c → Complex IV → O2
C)
NADH → Complex I → Complex II→ Complex III → Cyt c → Complex IV → O2
D)
FADH2 → Complex II → CoQ → Complex III → Cyt c → Complex IV → O2
E)
A and D.
Ans: E Section: 20.3
22.
Which of the following does not participate in, nor is a component of, the electron-transport
chain?
A)
coenzyme A
B)
non-heme, iron-sulfur proteins
C)
coenzyme Q
D)
cytochrome c1
E)
NADH
Ans: A Section: 20.3
23.
Electron flow down the electron-transport chain leads to the:
A)
transport of protons across the inner mitochondrial membrane from inside the matrix to
the intermembrane space.
B)
transport of protons across the inner mitochondrial membrane from the intermembrane
space into the matrix.
C)
coupled synthesis of GTP.
D)
a dangerous imbalance of K+ ions across the mitochondiral membrane.
E)
None of the above.
Ans: A Section: 20.3
24.
Coenzyme Q is also called:
A)
NADH.
D)
B)
oxidoreductase.
E)
C)
ubiquinone.
Ans: C Section: 20.2
Ans: Catalase Section: 20.3
Chapter 20 The Electron-Transport Chain
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25.
Which of the following does not pump protons?
A)
Complex I
D)
B)
Complex II
E)
C)
Complex III
26.
In proteins these amino acid residues usually complex to the iron-sulfur clusters.
A) Gly B) Arg C) Cys D) All of the above. E) None of the above.
Ans: C Section: 20.2
27.
What is a cytochrome?
A)
a protein that transfers electrons, and that also contains a heme prosthetic group
B)
a chloroplast protein that transfers electrons, and that also contains an iron sulfur
prosthetic group
C)
a protein that pumps ATP, and that also contains iron
D)
All of the above.
E)
None of the above.
Ans: A Section: 20.2
28.
In the Rieske center, the iron-sulfur center is coordinated to the amino acid(s) _______.
A) His B) Cys C) His and Cys D) Cys and Met E) None of the above.
Ans: A Section: 20.3
29.
The Q cycle:
A)
transfers electrons from a two-electron carrier to a one-electron carrier.
B)
recycles protons.
C)
acts as an NADH exchange with the cytosol.
D)
A and B.
E)
A, B, and C.
Ans: A Section: 20.3
30.
What pathologic condition(s) results from free-radical injury?
A) emphysema B) Parkinson’s disease C) diabetes D) atherogenesis E) All of the
above.
Ans: E Section: 20.3
31.
What evidence is there that modern mitochondria are the result of a single ancient event? What
is the event called?
A)
Modern mitochondria have specific transcription and translation machinery similar to
viruses: viral endosymbiosis event.
B)
Modern mitochondria have circular DNA similar to bacteria: endosymbiotic event.
C)
Modern mitochondria are the only organelles in the cell with a double membrane:
electron-transfer event.
D)
Modern mitochondria have DNA polymerase sequences similar to a single bacteria:
replication event.
E)
None of the above.
Ans: B Section: 20.1
Ans: B Section: 20.3
Chapter 20 The Electron-Transport Chain
5
32.
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.
33.
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.
Ans: C Section: 20.2
34.
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.
Ans: C Section: 20.2
Short-Answer Questions
35.
Draw the structure of a mitochondrion and indicate the sites of oxidative phosphorylation and
the citric acid cycle.
takes place in the matrix, while oxidative phosphorylation occurs in the inner
mitochondrial membrane. It should closely resemble text Figure 20.2.
Section: 20.1
Ans: D Section: 20.2
Chapter 20 The Electron-Transport Chain
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36.
Describe the path by which electrons from FADH2 enter the electron-transport chain.
37.
Explain why less ATP is made from the reoxidation of FADH2 as compared to NADH.
catalyzed by Complex II, Complex III, and Complex IV, fewer protons are pumped out of
the matrix as compared to NADH. Thus, fewer ATP molecules are ultimately made.
Section: 20.3
38.
Give the balanced equation for the net reaction catalyzed by Q-cytochrome c oxido-reducatase.
Section: 20.3
39.
What is a major defense strategy against oxidative damage caused by reactive oxygen species
(ROS)?
Ans:
Superoxide dismutase converts superoxide radicals to peroxide and oxygen (requires
protons), and catalase converts hydrogen peroxide to water and oxygen.
Section: 20.3
40.
The reduction potential of iron from Fe3+ to Fe2+ is +0.77V. How can it participate in multiple
exergonic redox reaction I electron transport?
in iron-sulfur centers and is found complexed with several different proteins and
cytochromes.
Section: 20.2
41.
Calculate the G° for the reaction where lactate + NAD+ is converted to pyruvate + NADH.
Section: 20.2
42.
What are the mechanisms that a cell uses to protect against production of oxygen radicals?
precursors to water and oxygen. The cell also uses other compounds to scavenge free
radicals such as glutathione and vitamins C and E.
Section: 20.3
43.
Describe the role that Q takes as the NADH-Q oxidoreductase transfers electrons from NADH
to coenzyme Q.
membrane and is part of the Q pool. In accepting the electrons, two protons are bound to
Q, resulting in a reduction of the lipophilic carrier.
Section: 20.2
complex. The FADH2 does not leave this complex, but transfers electrons to the iron
sulfur centers of the complex, and then to Q.
Section: 20.3
Chapter 20 The Electron-Transport Chain
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44.
What is the “dead zone” in the Gulf of Mexico and how did it come into being?
45.
In a table of reduction potentials, values for E° are given as plus (+) or minus (-). What is this in
reference to?
A standard half-cell apparatus is used to measure the E° for any redox couple. The
reduction potential is the observed voltage with reference to the standard half-cell
electrode containing 0.1 M H+ in equilibrium with one atmosphere H2 gas.
Section: 20.2
46.
In what direction do electrons flow in the electron-transport chain?
Ans:
The electron-transport chain proteins are arranged so that the electrons always flow to
components with a more positive reduction potential.
47.
For the reaction:
4 Cyt cred + 8 H+ matrix + O2 4 Cyt cox + 2 H2O + 4 H+ intermembrane space
the reduction of molecular oxygen to form water releases far more free energy than the 87.2
kJ/mol required to consume the protons from the matrix. What evidence is there that the excess
free energy is not lost simply as heat?
four protons that are pumped out of the matrix.
Nutrients from the Mississippi cause an explosive growth in phytoplankton with a
in the region, resulting in a hypoxic zone.