Deck 7: The Common Catabolic Pathway

Question 1

In the citric acid cycle, what reduced cofactors are derived from the oxidation of one molecule of acetyl-CoA to two molecules of CO₂?

A) 2 NADH and 1 FADH₂
B) 3 NADH and 1 FADH₂
C) 2 NADH and 2 FADH₂
D) 3 NADH and 2 FADH₂
E) 4 NADH and 2 FADH₂

Answer 1

3 NADH and 1 FADH₂

Question 2

If acetyl-CoA labeled with ¹⁴C, as shown in the figure to the right, were used as the substrate for the citric acid cycle, which of the following intermediates would be produced during the first round of the cycle?

A)

B)

C)

D)

E)

Answer 2

Question 3

Which of the following condenses with oxaloacetate to form citrate?

A) acetyl-CoA
B) cis-aconitate
C) carboxybiotin
D) oxalosuccinate
E) succinyl-phosphate

Answer 3

acetyl-CoA

Question 4

______ is used in the first reaction of the citric acid cycle and regenerated upon completion of one turn of the citric acid cycle.

Question 5

Aconitase catalyzes the _____ of citrate, followed by a _____ reaction.

A) oxidation; reduction
B) reduction; oxidation
C) hydration; dehydration
D) dehydration; hydration
E) isomerization; isomerization

Question 6

Given the following structure of isocitrate, the carbon labeled _____ is lost as CO₂ by isocitrate dehydrogenase, and the carbon labeled _____ is lost as CO₂ by $\alpha$ -ketoglutarate dehydrogenase.

A) 1; 2
B) 2; 1
C) 1; 3
D) 3; 1
E) 2; 3

Question 7

Considering the reactions within the citric acid cycle, which of the following molecules will be produced from the intermediate pictured on the right?

A) citrate
B) isocitrate
C) succinate
D) succinyl-CoA
E) $\alpha$ -ketoglutarate

Question 8

______ is the first compound that is oxidized in the citric acid cycle.

Question 9

Which of the following enzymes catalyzes a substrate-level phosphorylation?

A) malate synthase
B) succinate dehydrogenase
C) $\alpha$ -ketoglutarate dehydrogenase
D) succinyl-CoA synthetase
E) fumarase

Question 10

______ catalyzes a substrate-level phosphorylation reaction within the citric acid cycle.

Question 11

Which of the following enzymes contains an FAD prosthetic group?

A) pyruvate dehydrogenase
B) isocitrate dehydrogenase
C) succinate dehydrogenase
D) $\alpha$ -ketoglutarate dehydrogenase
E) malate dehydrogenase

Question 12

The oxidation of succinate to fumarate is best characterized as an oxidation of _____.

A) an alkane to an alkene
B) an alcohol to an aldehyde
C) an alcohol to a ketone
D) an aldehyde to a carboxylic acid
E) a $\beta$ -keto acid to CO₂ and a carboxylic acid that is one carbon smaller

Question 13

The reaction catalyzed by fumarase is _____.

A) an isomerization of an alcohol
B) a dehydration of an alcohol
C) a hydroxylation of an alkene
D) a hydration of an alkene
E) none of the above

Question 14

How does the reaction catalyzed by malate dehydrogenase proceed despite a $\Delta$ G $\degree$ ' of 29.7 kJ/mol?

A) An elevated [H⁺] allows the reaction to proceed.
B) High levels of NAD⁺ allow the reaction to proceed.
C) Concentrations of oxaloacetate are kept very low by rapid use in the subsequent step.
D) The enzyme is unique in its ability to catalyze the reaction in only one direction.
E) The enzyme catalyzed reaction under cellular conditions has a much smaller energy of activation.

Question 15

Which of the following is activated by ADP?

A) malate dehydrogenase
B) aconitase
C) isocitrate dehydrogenase
D) citrate synthase
E) succinyl-CoA synthetase

Question 16

Which of the following is inhibited by high levels of acetyl-CoA?

A) malate dehydrogenase
B) succinyl-CoA synthetase
C) pyruvate carboxylase
D) pyruvate dehydrogenase
E) $\alpha$ -ketoglutarate dehydrogenase

Question 17

Which of the following can cause a large increase in the activity of the citric acid cycle?

A) activation of isocitrate dehydrogenase by ADP
B) activation of $\alpha$ -ketoglutarate dehydrogenase by Ca²⁺
C) increasing concentrations of oxaloacetate by pyruvate carboxylase
D) increasing concentrations of $\alpha$ -ketoglutarate by transamination
E) all of the above

Question 18

Which of the following can be converted into glutamic acid in a single enzyme-catalyzed step?

A) isocitrate
B) oxaloacetate
C) malate
D) $\alpha$ -ketoglutarate
E) succinyl-CoA

Question 19

_____ and pyruvate can be combined in an ATP-dependent reaction that regenerates one of the key intermediates in the citric acid cycle.

Question 20

Which of the following is an anaplerotic reaction that is often used in the cell?

A) conversion of pyruvate to acetyl-CoA
B) conversion of $\alpha$ -ketoglutarate to glutamic acid
C) conversion of citrate to oxaloacetate and acetyl-CoA
D) conversion of pyruvate to oxaloacetate
E) conversion of succinyl-CoA to heme

Question 21

In the malate-aspartate shuttle, _____ is reduced to _____ in the cytosol.

A) aspartate; oxaloacetate
B) oxaloacetate; malate
C) aspartate; malate
D) malate; aspartate
E) malate; oxaloacetate

Question 22

In the malate aspartate shuttle, _____ is transferred into the mitochondria, and _____ is transferred to the cytosol.

A) NADH; NAD⁺
B) NAD⁺; NADH
C) malate; oxaloacetate
D) malate; aspartate
E) oxaloacetate; aspartate

Question 23

Complexes I and II each transfer electrons to ______.

Question 24

For eukaryotes, where are the complexes of electron transport located?

A) cytosol
B) outer mitochondrial membrane
C) mitochondrial intermembrane space
D) inner mitochondrial membrane
E) mitochondrial matrix

Question 25

For every two electrons transferred from NADH to oxygen, _____ protons are pumped from the matrix to the intermembrane space.

A) 4
B) 6
C) 8
D) 10
E) 12

Question 26

The process of _____ allows electrons to be transferred between redox centers that are up to 1.4 nm apart.

A) reduction
B) swinging arm electron transfer
C) electron shuttling
D) electron teleporting
E) tunneling

Question 27

What shuttle mechanism transfers cytosolic NADH into the mitochondria with a loss of reductive power, with the electrons entering the electron transport chain as ubiquinol instead of NADH?

A) glycerol-3-phosphate shuttle
B) alanine aminotransferase shuttle
C) malate-aspartate shuttle
D) adenine nucleotide shuttle
E) none of the above

Question 28

The reduction potentials of all prosthetic groups of Complex I have reduction potentials between _____ and _____.

A) NAD⁺; ubiquinone
B) NADH; ubiquinol
C) FAD; ubiquinone
D) ubiquinone; oxygen
E) ubiquinone; cytochrome c

Question 29

Which of the following represents the correct order of electron flow in Complex I?

A) NADH $\rightarrow$ ubiquinone $\rightarrow$ Fe-S clusters $\rightarrow$ FMN
B) NADH $\rightarrow$ Fe-S clusters $\rightarrow$ FMN $\rightarrow$ ubiquinone
C) NADH $\rightarrow$ FMN $\rightarrow$ ubiquinone $\rightarrow$ Fe-S clusters
D) NADH $\rightarrow$ FMN $\rightarrow$ Fe-S clusters $\rightarrow$ ubiquinone
E) NADH $\rightarrow$ ubiquinone $\rightarrow$ FMN $\rightarrow$ Fe-S clusters

Question 30

How many protons are transported from the matrix to the intermembrane space by Complex I?

A) 0
B) 2
C) 4
D) 6
E) 8

Question 31

Ubiquinone is found in the inner mitochondrial membrane, and cytochrome c is found in the matrix.

Question 32

Complex III accepts electrons from _____ and transfers them to _____.

A) cytochrome c; cytochrome a
B) ubiquinol; cytochrome c
C) ubiquinone; cytochrome c
D) ubiquinol; cytochrome b
E) ubiquinone; cytochrome a

Question 33

Which of the following results from the first round of the Q cycle?

A) two reduced cytochrome c and one ubiquinone
B) one reduced cytochrome c and one ubiquinone
C) one reduced cytochrome c, one reduced cytochrome B and one ubiquinone
D) two reduced cytochrome c and one ubiquinol
E) one reduced cytochrome c and one semiquinone

Question 34

How many cytochrome c molecules are oxidized by Complex IV for each molecule of oxygen that is reduced?

A) 1
B) 2
C) 3
D) 4
E) It depends upon the efficiency of the electron transfer in Complex IV.

Question 35

The cytochromes within Complex III all contain _____ groups.

Question 36

What is the terminal electron acceptor in aerobic organisms?

A) NAD⁺
B) FAD
C) ubiquinone
D) varies from one organism to another
E) none of the above

Question 37

Complex IV uses _____ and _____ ions to reduce oxygen to water.

A) manganese; iron
B) copper; iron
C) manganese; copper
D) zinc; copper
E) iron; zinc

Question 38

Which of the following occurs when the catalytic subunit of ATP synthase is in the loose state?

A) ADP and P_i bind.
B) ADP and P_i are converted to ATP.
C) ATP is hydrolyzed.
D) ATP is released.
E) None of the above

Question 39

The imbalance of protons across the inner mitochondrial membrane is referred to as _____.

A) the protonmotive force
B) the chemiosmotic force
C) the electron transport force
D) the ATP synthase force
E) the proton gradient force

Question 40

If the pH of the matrix is 7.7, what is the pH of the intermembrane space if the $\Delta$ G for transport of H⁺ is 20 kJ/mol at 37 $\degree$ C with $\Delta$$\Psi$ = 170 mV?

A) 2.6
B) 7.1
C) 8.3
D) 12.8
E) cannot be determined

Question 41

If the $\Delta$ G for the oxidation of NADH by oxygen is -220 kJ/mol and the $\Delta$ G for transport of H⁺ across the inner membrane is 20 kJ/mol, what is the efficiency for energy captured in the proton gradient versus energy evolved from NADH oxidation?

A) 9.1%
B) 36%
C) 45%
D) 73%
E) 91%