MODULE 11: Chapter 11.2

Question 1

Where do glycolysis and the citrate cycle take place?

Answer 1

Glycolysis takes place in the cytosol, while the citrate cycle occurs in the mitochondrial matrix.

Question 2

What initiates the electron transport system?

Answer 2

The oxidation of NADH by the mitochondrial electron transport system, starting with complex I.

Question 3

How many discrete electron carriers are involved in the electron transport system?

Answer 3

As many as 20 discrete electron carriers.

Question 4

What is the end product of the electron transport system?

Answer 4

The reduction of molecular oxygen to form water.

Question 5

What is the primary function of coenzyme Q in the electron transport system?

Answer 5

Coenzyme Q serves as a mobile electron carrier that transports electrons laterally in the membrane.

Question 6

What happens to ATP synthesis if electron transfer in the electron transport system is inhibited?

Answer 6

There is a loss of ATP synthesis by the ATP synthase complex.

Question 7

Name one inhibitor of the electron transport system.

Answer 7

Rotenone, hydrogen cyanide, carbon monoxide, or antimycin A.

Question 8

What are the four functional components of the electron transport system?

Answer 8

1. Three large multi-subunit protein complexes (I, III, IV)
2. Coenzyme Q (ubiquinone)
3. Three membrane-associated FAD-containing enzymes
4. Cytochrome c.

Question 9

What is the biochemical standard reduction potential (E°′) for NAD⁺/NADH?

Answer 9

-0.32 V.

Question 10

How do reduction potentials change throughout the electron transport system?

Answer 10

Reduction potentials generally increase with each reaction in the electron transport system.

Question 11

What is the role of cytochrome c in the electron transport system?

Answer 11

Cytochrome c carries electrons one at a time from complex III to complex IV.

Question 12

What is the mass and number of subunits for complex I?

Answer 12

Complex I has a mass of 850 kDa and contains 42 subunits.

Question 13

What prosthetic groups are associated with complex II?

Answer 13

FAD and Fe–S.

Question 14

What are the two mechanisms proposed for proton translocation across the membrane?

Answer 14

1. A redox loop mechanism
2. A redox-driven proton pump.

Question 15

How does complex I contribute to proton translocation?

Answer 15

Complex I translocates 4 H⁺ from the matrix side to the intermembrane space.

Question 16

What is the structure of complex I from mammals based on cryo-electron microscopy?

Answer 16

It is shaped like a sideways ‘L’ and contains more than 40 transmembrane α helices.

Question 17

What happens to the Fe–S centers during electron transfer in complex I?

Answer 17

They carry one electron at a time from one end of the complex to the other.

Question 18

What is the reduction potential of O2/H2O?

Answer 18

+0.82 V.

Question 19

What is the result of the oxidation of NADH in complex I?

Answer 19

The reduction of coenzyme Q to form QH2 (ubiquinol) and the translocation of protons.

Question 20

Fill in the blank: Complex II is also known as _______.

Answer 20

succinate dehydrogenase.

Question 21

True or False: Complex IV is the least abundant complex in the electron transport system.

Answer 21

False.

Question 22

What is the main role of FMN in complex I?

Answer 22

FMN accepts two electrons from NADH.

Question 23

What is the total number of protons translocated when electrons are derived from FADH2?

Answer 23

6 H⁺.

Question 24

What does the Q cycle in complex III utilize?

Answer 24

A redox loop mechanism for proton translocation.

Question 25

What is the function of the iron-sulfur (Fe–S) centers in complex I?

Answer 25

They facilitate electron transfer through redox reactions.

Question 26

What is the effect of rotenone on complex I?

Answer 26

It blocks electron transfer by preventing a redox reaction between two Fe–S centers.

Question 27

What is the equation for the reaction involving NADH and coenzyme Q?

Answer 27

NADH + Q + 5 H⁺ → NAD⁺ + QH₂ + 4 H⁺ ## Footnote This equation represents the transfer of electrons from NADH to coenzyme Q.

Question 28

What are the three critical roles of coenzyme Q in the electron transport system?

Answer 28

* Mobile electron carrier transporting electrons between complexes I, II, and III * Entry point for electron pairs from citrate cycle, fatty acid oxidation, and glycerol-3-phosphate dehydrogenase * Converts 2 e− transport system into 1 e− transport system in complex III via the Q cycle

Question 29

What is the hydrophobic tail of coenzyme Q made of?

Answer 29

Repeating isoprenoid units ## Footnote In humans, the hydrophobic tail consists of 10 isoprenoid units, totaling 50 carbons.

Question 30

What is the common name for coenzyme Q with a hydrophobic tail of 10 isoprenoid units?

Answer 30

Coenzyme Q10 or CoQ10 ## Footnote CoQ10 is sold as an over-the-counter nutritional supplement.

Question 31

What is the function of succinate dehydrogenase in complex II?

Answer 31

Catalyzes the oxidation of succinate to fumarate and transfers electrons to FAD ## Footnote It participates in both the electron transport chain and the citrate cycle.

Question 32

What is the net reaction of succinate oxidation by succinate dehydrogenase?

Answer 32

Succinate + FAD → Fumarate + FADH₂ ## Footnote The electron pair from succinate is transferred to FAD.

Question 33

What components are found in mammalian succinate dehydrogenase?

Answer 33

* Three iron–sulfur centers (two 4 Fe–4 S and one 2 Fe–2 S) * A b-type heme (cytochrome b560)

Question 34

What is the function of complex III in the electron transport chain?

Answer 34

Transfers electrons from QH₂ to cytochrome c one at a time ## Footnote Complex III has multiple protein subunits and serves as a docking site for QH₂.

Question 35

What are the two binding sites for ubiquinone in complex III called?

Answer 35

QP and QN ## Footnote QP is closer to the intermembrane space and QN is closer to the mitochondrial matrix.

Question 36

What is the overall reaction of QH₂ oxidation by complex III?

Answer 36

QH₂ + 2 H⁺ → Q + 4 H⁺ + 2 reduced cytochrome c ## Footnote This reaction translocates protons across the membrane.

Question 37

What is cytochrome c?

Answer 37

A small protein (∼13 kDa) that transports one electron from complex III to complex IV ## Footnote It contains a heme group that binds iron.

Question 38

What distinguishes oxidized and reduced cytochrome c?

Answer 38

Oxidized cytochrome c contains ferric iron (Fe³⁺) and reduced cytochrome c contains ferrous iron (Fe²⁺)

Question 39

What types of cytochromes are there, and how are they classified?

Answer 39

* Type a * Type b * Type c ## Footnote They are classified based on the type of heme group they contain.

Question 40

What is the absorption spectrum of reduced cytochrome c?

Answer 40

Shows peaks at 418 nm (γ), 534 nm (β), and 554 nm (α) ## Footnote Different cytochromes have distinct absorption spectra.

Question 41

What is the function of complex IV in the electron transport chain?

Answer 41

Accepts electrons from cytochrome c and donates them to oxygen to form water ## Footnote This process translocates protons across the membrane.

Question 42

What components are found in mitochondrial complex IV?

Answer 42

* Two copper centers (CuA and CuB) * Two heme groups (one in cytochrome a and one in cytochrome a3)

Question 43

How does cytochrome c interact with complex IV?

Answer 43

Binds near CuA, which accepts electrons in a coupled redox reaction ## Footnote This interaction leads to the oxidation of cytochrome c.

Question 44

What is the structure of the human complex IV protein?

Answer 44

It includes 14 subunits, two copper centers, and two hemes identified using high-resolution cryo-electron microscopy.

Question 45

How many H⁺ are involved in the complex IV reactions?

Answer 45

A total of four H⁺ are involved: 2 H⁺ translocated into the intermembrane space and 2 H⁺ used to form H2O.

Question 46

What is the function of cytochrome c in the electron transport system?

Answer 46

Cytochrome c transports only 1 e− at a time and must make two trips to transfer a pair of electrons from NADH or FADH2 to O2.

Question 47

What is the difference in H⁺ translocation between complex I and complex II?

Answer 47

Complex I translocates 10 H⁺, while complex II translocates only 6 H⁺.

Question 48

What is proton-motive force?

Answer 48

The contributions of ΔpH and Δψ to the stored energy in the electrochemical proton gradient.

Question 49

What is the equation for calculating the change in biochemical standard free energy (ΔG°′)?

Answer 49

ΔG°′ = −nFΔE°′

Question 50

What are the E°′ values for NAD⁺/NADH and O2/H2O?

Answer 50

NAD⁺/NADH is −0.32 V and O2/H2O is +0.82 V.

Question 51

What is the ΔG°′ for translocation of 10 H⁺ across the membrane when NADH is oxidized?

Answer 51

ΔG°′ = −220.0 kJ/mol of NADH oxidized.

Question 52

What is the ΔG value for the proton-motive force at 37 °C?

Answer 52

ΔG = −20.80 kJ/mol.

Question 53

What is the efficiency of the electron transport system based on free energy calculations?

Answer 53

Approximately 94%.

Question 54

What role does coenzyme Q play in the electron transport system?

Answer 54

Coenzyme Q is a mobile electron carrier that transports a pair of electrons (2 e−) in its reduced form of QH2.

Question 55

What is the theoretical yield of ATP per NADH based on the change in free energy of −208 kJ/mol?

Answer 55

Theoretical yield is calculated using a value of ∼40 kJ/mol for ATP synthesis.

Question 56

What is the actual yield of ATP per NADH?

Answer 56

Approximately 2.5 ATP/NADH.

Question 57

What might account for the difference in efficiency based on free energy calculations and ATP yields?

Answer 57

Differences in energy conversion efficiencies in oxidative phosphorylation.

Question 58

What are iron–sulfur (Fe–S) centers?

Answer 58

Electron carrier prosthetic groups found in complexes I, II, and III of the electron transport system.

Question 59

Fill in the blank: The term _______ describes the potential energy of the proton concentration gradient plus the charge difference across the membrane.

Answer 59

proton-motive force