Chapter 19: ETC & Oxidative Phosphorylation

Question 1

how can you determine the direction of electron flow in redox reactions using the standard reduction potentials (E°′)?

Answer 1

electrons will flow in the direction of the lower E°′ value

Question 2

how can you determine if an electron transfer equation will be endergonic or exergonic given the standard reduction potentials (E°′)?

Answer 2

exothermic reactions release energy and have a negative DG, endothermic reactions absorb energy and have a positive DG
DG = -nFE°′
n = # moles transfered
F = 96,485 C/mol

Question 3

which of the following is used as a substrate in the electron transport chain to produce energy for the
cell?
a. CO2
b. oxygen
c. acetyl CoA
d. NAD+
e. FADH

Answer 3

e. FADH

Question 4

mitochondrial electron transport relies on…
a. a membrane that is impermeable for protons
b. reduced compounds that serve as electron donors
c. hydrophobic redox carriers with increasing values for the redox potential, E
d. a soluble electron carrier
e. all of the above are correct

Answer 4

e. all of the above are correct

Question 5

during oxidative phosphorylation :
a. phosphate is oxidized
b. a proton gradient is used by ATP synthase to generate ATP
c. a compound X transfers a phophate, Pi, to ADP
d. NADP serves as phosphate donor

Answer 5

b. a proton gradient is used by ATP synthase to generate ATP

Question 6

FADH 2 can feed its electrons into the mitochondrial electron chain (ETC) at complex II, thus its redox
potential, E, is probably
a. the same as complex I
b. the same as complex II
c. more negative than that of complex II
d. more positive than complex III
e. about the same as water

Answer 6

c. more negative than that of complex II

Question 7

the ATP yield from NADH+H + feeding its electrons into the electron transport chain is higher than from FADH 2 because
a. NADH+H + has more electrons than FADH 2
b. NADH+H + has more protons than FADH 2
c. NADH+H + feeding its electrons into ETC leads to more protons being translocated than when FADH 2 donates its electrons
d. NADH+H + uses a different, more efficient mechanism than FADH 2 to generate ATP
e. ATP synthesis and heat generation will stay the same

Answer 7

c. NADH+H + feeding its electrons into ETC leads to more protons being translocated than when FADH 2 donates its electrons

Question 8

the primary role of oxygen in cellular respiration is to____________
a. catalyze the reactions of glycolysis
b. combine with carbon, forming CO2
c. yield energy in the form of ATP as it is passed down the respiratory chain
d. act as an acceptor for electrons and hydrogen, forming water
e. combine with lactate, forming pyruvate

Answer 8

d. act as an acceptor for electrons and hydrogen, forming water

Question 9

which of the paths outlined below best describes the path the electrons from NADH + H + would take through the electron transport chain?
a. complexes I, II and III
b. complexes I, III and IV
c. complexes II, III, and IV
d. complexes III, IV and V
e. complexes I, II and IV

Answer 9

b. complexes I, III and IV

Question 10

the oxidation of FADH 2 is accompanied by the translocation of a total of ______ protons across the mitochondrial membrane
a. 2
b. 4
c. 6
d. 8
e. 10

Answer 10

c. 6

Question 10

the only soluble component of the ETC is…
a. complex I
b. succinate DH
c. coenzyme Q
d. cytochrome c
e. PS II

Answer 10

d. cytochrome c

Question 11

the ultimate electron accepter in the electron transport chain is
a. CO2
b. H2O
c. O2
d. glucose
e. pyruvate

Answer 11

c. O2

Question 12

the final product of electron transport is ________
a. water
b. ADP
c. NADPH
d. ATP
e. FMNH 2

Answer 12

a. water
d. ATP

Question 13

the NADH+H + that is generated in glycolysis can be transferred into the mitochondria by which of the
following processes?
a. glycerol-3-phosphate shuttle
b. malate-aspartate shuttle
c. phosphate shuttle
d. calvin cycle
e. a and b are correct

Answer 13

e. a and b are correct

Question 14

coenzyme Q is very hydrophobic, thus can easily move laterally through the lipid membrane, during electron transport it has the following function…
a. it dissipates the proton gradient
b. it accepts electrons directly from NADH
c. it can accept electrons from complex I or complex II and transfer them to complex III
d. it reduces oxygen to water
e. it is not a part of the electron transport chain

Answer 14

c. it can accept electrons from complex I or complex II and transfer them to complex III

Question 15

the uncoupler DNP (dinitrophenol) has been used as a diet pill because it
a. is available over the internet
b. leads to a rapid rate of ETC without the production of ATP
c. is cheap
d. is considered a safe drug
e. suppresses your appetite

Answer 15

b. leads to a rapid rate of ETC without the production of ATP

Question 16

Peter Mitchell formulated the chemiosmotic theory in 1961, which statement is NOT part of his model?
a. a high energy compound X to store the energy
b. a proton gradient
c. a semipermeable membrane
d. an electrical gradient
e. Proton motive force

Answer 16

a. a high energy compound X to store the energy

Question 17

the electron donor for the mitochondrial ETC is _________
a. O2
b. H2O
c. NADH+H +
d. NADP +
e. CO2

Answer 17

c. NADH+H +

Question 18

under aerobic conditions, the terminal electron acceptor in muscle cells is ______; under anaerobic conditions it is _____
a. NADH+H + ; H 2O
b. O2; NADH+H +
c. O2; Pyruvate
d. NADH+H + ; Pyruvate

Answer 18

b. O2; NADH+H +

Question 19

what would happen if you could artificially increase the proton concentration in the intermembrane space of the mitochondria ?
a. increased ATP production
b. increased levels of H 20
c. decreased levels of oxidative phosphorylation
d. increase oxygen consumption

Answer 19

a. increased ATP production
because an elevated proton concentration gradient across the inner mitochondrial membrane drives protons back across the membrane through ATP synthase which drives ATP formation

Question 20

assume you would add an inhibitor of mitochondrial electron transport that inhibits complex III
a. predict the effect on the proton gradient
b. how would that affect ATP synthesis?

Answer 20

a. inhibiting complex III would disrupt the flow of electrons through the electron transport chain which would reduce the pumping of protons across the inner mitochondrial membrane, ultimately leading to a decrease in the proton gradient across the membrane
b. with a decreased proton gradient, there would be a reduced driving force for ATP synthesis, resulting in a decrease in ATP production

Question 21

what would happen if you added an uncoupler like DNP to the reaction that was inhibited at complex III?
a. ETC would …
b. ATP synthesis would …
c. how would this affect the oxidation states of the complexes?

Answer 21

a. DNP would dissipate the proton gradient by creating a channel for protons to freely move across the mitochondrial membrane, uncoupling the electron transport from ATP synthesis
b. ATP synthesis would decrease
c. oxidation states of the complexes remain unchanged

Question 22

in another experiment (you may refer to the same cartoon) you are inhibiting ATP synthase directly using oligomycin
a. ETC would …
b. ATP synthesis would …
c. how would this affect the oxidation states of the complexes?

Answer 22

a. without ATP synthase functioning, the buildup of the proton gradient would eventually halt the ETC due to the lack of an outlet for the accumulated protons
b. ATP synthesis would stop
c. inhibition of ATP synthase would prevent the flow of protons back into the mitochondrial matrix, leading to a buildup of the proton gradient and a decrease in the oxidation states of the complexes as they are unable to transfer electrons in the absence of ATP synthesis

Question 23

briefly describe what you expect to happen to the electron transport and the ATP synthesis when you add an uncoupler like DNP to this assay?
a. ETC would …
b. ATP synthesis would …
c. how would this affect the oxidation states of the complexes?

Answer 23

a. ETC would remain intact
b. energy from ETC cannot be used for ATP synthesis due to the breakdown of the proton gradient
c. oxidative states are not affected

Question 24

state the location of the low pH environment created by the electron transport chain, why does this high proton concentration not dissipate into the cytosol?

Answer 24

the low pH environment created by the electron transport chain is located in the intermembrane space of the mitochondria, this high proton concentration does not dissipate into the cytosol because the inner mitochondrial membrane is impermeable to protons, protons are coupled to the synthesis of ATP, preventing the protons from freely diffusing back into the cytosol

Question 25

consider an organism, such as E. coli, which is able to grow both in aerobic and anaerobic conditions, under which conditions would you expect to see the fastest or most vigorous growth? justify your answer by
contrasting the catabolic pathways available under aerobic vs anaerobic conditions

Answer 25

E. coli would likely exhibit faster and more vigorous growth under aerobic conditions where aerobic respiration provides a higher energy yield per glucose molecule because the abundance of ATP generated in aerobic respiration fuels cellular processes more efficiently, enabling rapid growth and replication

Question 26

consider E. coli growing on glucose under anaerobic and aerobic conditions, which culture would probably run out of glucose first and why?

Answer 26

because aerobic respiration is more efficient in extracting energy from glucose compared to anaerobic pathways like fermentation, the culture of E. coli growing under aerobic conditions is likely to consume glucose at a faster rate

Question 27

describe the effect on the rate of the ETC (faster, slower, stopped, no effect) under each of the following
hypothetical conditions:
a. hole/break in the mitochondrial inner membrane ______________
b. hole/break in the mitochondrial outer membrane ______________
c. high rate of glycolysis _________
d. low availability of oxygen ________
e. inhibition of electron transfer at complex I _________
f. inhibition of ATP synthase without a decoupler ____________
g. lowered pH in the mitochondrial matrix ________________

Answer 27

a. slower
b. no effect
c. faster
d. slower
e. stopped
f. slower
g. faster

Question 28

both NADH+H + and FADH 2 are electron carriers that feed into the ETC, explain why NADH+H + produces more ATP than FADH 2

Answer 28

NADH+H+ produces more ATP than FADH2 due to the difference in the energy yield during the electron transport chain (ETC), FAD takes less energy to reduce than does NAD+; so when the opposite (oxidation) occurs, more energy is released from NADH than from FADH2

Question 29

what is the role of oxygen in aerobic respiration?

Answer 29

serves as the final electron acceptor

Question 30

where do cells use oxygen?
a. hemoglobin
b. ETC
c. TCA cycle
d. glycolysis
e. glyoxylate cycle

Answer 30

b. ETC during aerobic respiration

Question 31

cytochrome C is the only soluble component of the ETC, cytC transfers electrons from Complex III to complex IV in the ETC, if you inhibited the ETC at complex III what would happen to the absorbance of 400 nm and at 560 nm?
a. increase at 400 nm and 560 nm
b. decrease at 400 nm and 560 nm
c. decrease at 400 nm and increase at 560 nm
d. increase at 400 nm and decrease at 560 nm
explain…

Answer 31

c. decrease at 400 nm and increase at 560 nm
the inhibition of the ETC at complex III would lead to a reduction in the oxidized state of cytochrome C, causing a decrease in absorbance at 400 nm (where oxidized cytochrome C absorbs) and an increase in absorbance at 560 nm (where reduced cytochrome C absorbs more)

Question 32

to study electron transport, complex I was inhibited, addition of ADP, Pi and _________ should still allow ATP
production
a. succinate
b. NADH
c. oxygen
d. lactate
because…

Answer 32

a. succinate
because succinate bypasses the inhibited complex I and directly enters the electron transport chain (ETC) at complex II

Question 33

what would happen to ATP synthesis if membrane integrity were disturbed, i.e, the inner mitochondrial the membrane would become leaky?

Answer 33

if the inner mitochondrial membrane becomes leaky, it would lead to a decrease in ATP synthesis since it would cause the proton motive force to dissipate

Question 34

coupling of ETC and ATP synthesis means…
a. if oxygen is consumed than ATP is made
b. if oxygen is produced than ATP is used
c. if oxygen is consumed, then ATP is not made
d. if oxygen in produced than ATP is not used

Answer 34

a. if oxygen is consumed than ATP is made

Question 35

which species of CytC would you expect for the different ETC inhibitors:
a. rotenone
b. antimycin A
c. CN -

Answer 35

a. CytCred
b. CytCox
c. CytCox
CytCred has gained electrons (reduced) and CytCox has lost electrons (oxidized)

Question 36

when is oxygen produced during ETC?
a. when ATP synthase works
b. when ETC is inhibited by CN-
c. when ATP synthase is inhibited by oligomycin
d. never
e. always

Answer 36

d. never
oxygen is not produced during the Electron Transport Chain (ETC); rather, it is consumed as the final electron acceptor in aerobic respiration

Question 37

__________________ is a measure of ETC activity

Answer 37

the rate of oxygen consumption

Question 38

succinate feeds electrons in at ________________

Answer 38

complex II

Question 39

the effect of CN- is ________________

Answer 39

to inhibit complex IV, also known as cytochrome c oxidase

Question 40

which statement is true for the graph shown in Fig.1?
a. the figure shows two independent processes
b. after addition of CN- the cell runs out of ADP concentrations
are too low
c. [NAD+] is too low to be reduced to NADH+ H+
d. when CN- is added the proton gradient dissipates and can no
longer fuel ATP synthase

Answer 40

d. when CN- is added the proton gradient dissipates and can no longer fuel ATP synthase

Question 41

how many protons are translocated during ETC? where will these protons be used?

Answer 41

4 protons per pair of electrons these protons are used to create a proton gradient across the inner mitochondrial membrane

Question 42

dinitrophenol (DNP) uncouples ETC from ATP synthesis by
a. dissipating the proton gradient
b. inhibiting ATP synthesis
c. inhibiting ETC
d. preventing electrons from succinate to enter the ETC

Answer 42

a. dissipating the proton gradient

Question 43

which is true/false for ATP synthase via ATP synthase
a. Under standard conditions ATP synthesis is near equilibrium, ΔG⁰’ = 0 kJ/mol
b. ATP release is triggered by a conformation change of the β – subunit
c. proton flow through the Fo complex turns the F1 complex eliciting a conformation change
d. Paul Boyer won a Nobel prize for elucidating the mechanism of ATP synthesis by ATP synthase
e. a high energy phosphorylated intermediate is formed during ETC
f. the motor is fueled by the proton gradient

Answer 43

a. false
b. true
c. true
d. true
e. true
f. true

Question 44

why do people that accidentally ingest DNP sweat extensively and lose weight rapidly?

Answer 44

DNP disrupts the process of ATP production in cells by uncoupling oxidative phosphorylation, this means that the energy normally used for ATP synthesis is instead released as heat, causing an increase in metabolic rate and a rise in body temperature

Question 45

explain how the actin filament attached to the ATP synthase in the cartoon can be used to show that ATP synthesis involves the rotation of the F1 complex

Answer 45

the Fo complex allows protons to flow through it, creating a proton gradient, this flow of protons drives the rotation of the central rotor within the Fo complex, the F1 complex, on the other hand, contains the catalytic sites responsible for ATP synthesis, it’s linked to the Fo complex, and their connection allows for a mechanical coupling between proton flow and ATP synthesis

Question 46

Herbert Boyer showed that the phosphorylation of ADP to ATP does not require the proton gradient, for which process is the gradient required then?

Answer 46

ATP synthesis in oxidative phosphorylation

Question 47

during aerobic respiration, the products of one molecule of glucose generate a net of _______________ATP equivalents

Answer 47

38 ATP

Question 48

the NADH+H + in glycolysis can either account for 3 ATP or 5 ATP, which metabolic process is responsible for the difference in ATP yield?

Answer 48

in aerobic respiration NADH+H⁺ generated in glycolysis goes on to participate in the electron transport chain (ETC) in the mitochondria where each NADH+H⁺ can potentially yield about 3 ATP through oxidative phosphorylation, in the case of anaerobic conditions, the 2 NADH+H+ molecules can be converted to 3 ATP through the process of anaerobic glycolysis, where pyruvate is converted to lactate or ethanol, regenerating NAD+ for further glycolysis

Question 49

the ATP synthase only requires 3 H+ /ATP generated, thus the total ATP yield per NADH+H+ should be 3.3 ATP, however, experimental data show a yield closer to 2.5 ATP/NADH, explain…

Answer 49

ATP synthase is powered by a proton gradient, for every 4 H+ ions that cross the membrane 1 ATP is formed, as a result, the 10 H+ ions pumped out by the electron transport chain for each NADH molecule would theoretically yield 2.5 ATP as opposed to 3