Discussion chapter 7

Question 1

The citric acid cycle is often described as amphibolic, because ________.

it can operate both in the presence and absence of oxygen

it can oxidize both carbons and nitrogens equally well

it plays a role in both catabolism and anabolism

it is both reversible and irreversible

Answer 1

it plays a role in both catabolism and anabolism

Question 2

___________________ is the end product of the citric acid cycle’s regeneration phase.

Answer 2

Oxaloacetate.

Question 3

Select the three citric acid cycle intermediates replenished by anaplerosis in the order they enter the cycle.

Answer 3

1. Alpha-Ketoglutarate
   2- Succinyl-CoA
   3- Oxaloacetate

Question 4

Which citric acid cycle intermediate is replenished by the following anaplerotic reactions?

1- Carboxylation of pyruvate

2- Transamination of aspartate

3-Transamination of glutamate

Answer 4

1- Oxaloacetate
2-Oxaloacetate
3- Alpha-Ketogluturate

Question 5

Ethanol is oxidized to form acetate in the liver. Acetate is then converted to acetyl-CoA. How many molecules of ATP would be generated during the conversion of ethanol to acetate? Note that 2 mols of NADH are produced. Assume that one NADH is equivalent to 2.5 ATP and one FADH2 is equivalent to 1.5 ATP molecules.

14

15

5

30

Answer 5

15

Question 6

Which of the following enzymes catalyze oxidation reactions in the citric acid cycle?

i. Succinate dehydrogenase.
ii. Pyruvate dehydrogenase.
iii. Glycerol-3-phosphate dehydrogenase.
iv. α-Ketoglutarate dehydrogenase.

i, ii, and iv

i and iv

i, iii, and iv

All of the listed enzymes

Answer 6

i and iv

Question 7

If a suspension of mitochondria is mixed with Antimycin A which inhibits cyt b in complex III, which among the following would increase in concentration?

NAD

Oxidized cytochrome c

Reduced cytochrome c

NADH

Ubiquinol

Answer 7

NADH

Question 8

The four complexes of the electron transport chain use the energy of electrons stored in reducing agents to create a concentration gradient of protons (H+) across the mitochondrial inner membrane. Give the number of protons pumped into the intermembrane space by each of the four complexes:

complex I:
complex II:
complex III:
complex IV:

Answer 8

1. 4H+
2. 0
3. 4H+
4. 2H+

Question 9

Cyanide blocks electron transport through complex IV. Which of the following will occur if cyanide is added to cells?

O2 consumption will decrease.

The rate of citric acid cycle will increase.

NADH and FADH2 will be depleted.

ATP synthesis will increase.

Answer 9

O2 consumption will decrease.

Question 10

If the transfer of electrons in tightly coupled mitochondria is inhibited between complex III and complex IV which of the following will occur?

Oxygen consumption will increase.

The H+ ion concentration gradient will be dissipated.

Electron transfer from NADH will stop.

The synthesis of ATP will increase.

Answer 10

Electron transfer from NADH will stop.

Question 11

Which of the following statements regarding oxidative phosphorylation is TRUE?

The rate of ATP synthesis depends on the magnitude of the proton electrochemical gradient.

The smaller the electrochemical gradient, the faster the Pi- H+ symporter works.

Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur.

The addition of an uncoupler decreases the rate of reoxidation of NADH and FADH2, therefore decreasing the rate of the citric acid cycle.

Answer 11

Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur.

Question 12

Which of the following are TRUE statements regarding the structure of ATP synthase?

It has a membrane-embedded component called F0 and a component found in the matrix referred to as F1.

The γ subunit acts as the proton “wire” allowing equilibration of the ion gradient.

Research indicates that the F1 portion of the protein rotates in a circular counterclockwise direction.

Answer 12

It has a membrane-embedded component called F0 and a component found in the matrix referred to as F1.

Question 13

Which of the following describes the isomerization of citrate to isocitrate?

a major regulatory step for the citric acid cycle

an oxidation reaction

the only unnecessary step of the citric acid cycle

protects cells from the toxic effects of arsenite ion

converts a tertiary alcohol that cannot easily be oxidized to a secondary alcohol that can be oxidized

Answer 13

converts a tertiary alcohol that cannot easily be oxidized to a secondary alcohol that can be oxidized

Question 14

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

Answer 14

Isocitrate

Question 15

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

malate synthase

succinate dehydrogenase

α-ketoglutarate dehydrogenase

succinyl-CoA synthetase

fumarase

Answer 15

succinyl-CoA synthetase

Question 16

Which reaction below produces GTP in the citric acid cycle?

isocitrate → α-ketoglutarate

α-ketoglutarate → succinyl CoA

succinyl CoA → succinate

fumarate → malate

malate → oxaloacetate

Answer 16

succinyl CoA → succinate

Question 17

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

an alkane to an alkene

an alcohol to an aldehyde

an alcohol to a ketone

an aldehyde to a carboxylic acid

a β-keto acid to CO2 and a carboxylic acid that is one carbon smaller

Answer 17

an alkane to an alkene

Question 18

The reaction catalyzed by fumarase is _____.

an isomerization of an alcohol

a dehydration of an alcohol

a hydroxylation of an alkene

a hydration of an alkene

none of the above

Answer 18

a hydration of an alkene

Question 19

How does the reaction catalyzed by malate dehydrogenase proceed despite a ∆Go’ of 29.7 kJ/mol?

An elevated [H+] allows the reaction to proceed.

High levels of NAD+ allow the reaction to proceed.

Concentrations of oxaloacetate are kept very low by rapid use in the subsequent step.

The enzyme is unique in its ability to catalyze the reaction in only one direction.

The enzyme catalyzed reaction under cellular conditions has a much smaller energy of activation.

Answer 19

Concentrations of oxaloacetate are kept very low by rapid use in the subsequent step.

Question 20

How many electrons are transferred from one acetyl group when it is converted to two carbon dioxide molecules in the citric acid cycle?

2

4

6

8

10

Answer 20

8

Question 21

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

malate dehydrogenase

succinyl-CoA synthetase

pyruvate carboxylase

pyruvate dehydrogenase

Answer 21

pyruvate dehydrogenase

Question 22

An individual with a shortage of B vitamins (which include thiamine and riboflavin) may feel fatigued because of decreased pyruvate dehydrogenase activity. Which of the following would be true regarding this shortage?

The amount of acetyl CoA produced from carbohydrate metabolism that enters the citric acid cycle would be decreased.

A decrease in the amount of NADH would likely decrease activity of citrate synthase.

Flux through the citric acid cycle would cease until adequate pyruvate is available.

None of the above

All of the above

Answer 22

The amount of acetyl CoA produced from carbohydrate metabolism that enters the citric acid cycle would be decreased.

Question 23

Which of the following represents a point of regulation for the citric acid cycle?

I. pyruvate dehydrogenase complex
II. aconitase
III. isocitrate dehydrogenase
IV. fumarase

I, II, III, IV

I, II, IV

II, III

I, III

I, IV

Answer 23

I, III

Question 24

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

isocitrate

oxaloacetate

malate

α-ketoglutarate

succinyl-CoA

Answer 24

α-ketoglutarate

Question 25

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

Answer 25

CO2

Question 26

Which of the following uses intermediates of the citric acid cycle? I. gluconeogenesis II. amino acid biosynthesis III. fatty acid oxidation IV. glycolysis I only II only I, II, III I, II I, IV

Answer 26

I and II.

Question 27

The electrons formed from the aerobic oxidation of glucose are _____. I. ultimately transferred to O2 after several other transfer reactions II. transferred to the coenzymes NAD+ and FAD III. directly transferred to O2 during the citric acid cycle IV. transferred to succinate and arachidonic acid I only II only I, II II, III, IV I, II, III

Answer 27

I, II

Question 28

Which of the following statements is(are) true about oxidative phosphorylation? I. Electron transport provides energy to pump protons into the intermembrane space. II. An electrochemical gradient is formed across the inner mitochondrial membrane. III. Potassium and sodium ions form an ionic gradient across the inner mitochondrial membrane. IV. Complexes I, III, IV actively transport protons into the intermembrane space during electron transport. I, II, III, IV I, II, IV II, III, IV I, IV II, IV

Answer 28

I, II, IV

Question 29

In the electron transport chain, electrons are passed from redox center to redox center ____. spontaneously because of the redox potential gradient in an ATP dependent fashion because of the addition of free energy because of the proton gradient with the assistance of a carrier protein

Answer 29

spontaneously because of the redox potential gradient

Question 30

In eukaryotes, the citric acid cycle occurs in the _____ and therefore requires that reactants of the citric acid cycle be transported from the _____. cytosol; mitochondrial matrix mitochondrial matrix; cytosol endoplasmic reticulum; mitochondrial matrix inner mitochondrial membrane; mitochondrial matrix outer mitochondrial membrane; cytosol

Answer 30

mitochondrial matrix; cytosol

Question 31

Complexes I and II each transfer electrons to ___________________.

Answer 31

Ubiquinone or Coenyme Q

Question 32

For every two electrons transferred from NADH to oxygen, _____ protons are pumped from the matrix to the intermembrane space. 4 6 8 10 12

Answer 32

10

Question 33

Electrons from FADH2 are delivered to _____, and electrons from NADH are delivered to _____ of the electron transport chain. Complex I; Complex II Complex I; Complex III Complex II; Complex III Complex II; Complex I Complex I; Complex IV

Answer 33

Complex II; Complex III

Question 34

The reduction potentials of all prosthetic groups of Complex I have reduction potentials between _____ and _____. NAD+; ubiquinone NADH; ubiquinol FAD; ubiquinone ubiquinone; oxygen ubiquinone; cytochrome c

Answer 34

NAD+; ubiquinone

Question 35

Which of the prosthetic groups listed can accept or donate either one or two electrons because of the stability of the semiquinone state? cytochrome c NADH ubiquinone [2Fe-2S] Rieske center

Answer 35

ubiquinone

Question 36

Complex III accepts electrons from _____ and transfers them to _____. cytochrome c; cytochrome a ubiquinol; cytochrome c ubiquinone; cytochrome c ubiquinol; cytochrome b ubiquinone; cytochrome a

Answer 36

ubiquinol; cytochrome c

Question 37

How many protons are moved across the inner mitochondrial membrane at Complex III? 1 2 3 4 none of the above

Answer 37

4

Question 38

Which of the following results from the first round of the Q cycle? two reduced cytochrome c and one ubiquinone one reduced cytochrome c and one ubiquinone one reduced cytochrome c, one reduced cytochrome B and one ubiquinone two reduced cytochrome c and one ubiquinol one reduced cytochrome c and one semiquinone

Answer 38

one reduced cytochrome c and one semiquinone

Question 39

How many cytochrome c molecules are oxidized by Complex IV for each molecule of oxygen that is reduced? 1 2 3 4 It depends upon the efficiency of the electron transfer in Complex IV.

Answer 39

4

Question 40

What is the terminal electron acceptor in aerobic organisms? NAD+ FAD ubiquinone varies from one organism to another none of the above

Answer 40

none of the above

Question 41

A poison that prevents the transfer of electrons from the last [Fe-S] cluster of Complex I to coenzyme Q is added to a suspension of actively respiring mitochondria. Which of the following will be observed? ATP production would be impaired due to the uncoupling of oxidative phosphorylation from electron transport. ATP production would be reduced because of inhibition of the CoQ subunit of ATP synthase. ATP production would be reduced because of a decrease in the number of protons pumped out of the mitochondrial matrix. ATP production would be halted completely because of the block in electron transport through the electron transport chain. ATP production would be maintained at the normal rate because of functional overlap between Complex I and Complex II.

Answer 41

ATP production would be reduced because of a decrease in the number of protons pumped out of the mitochondrial matrix.

Question 42

Which conformation of the active sites in ATP synthase allows binding of substrates? A) L state B) O state C) T state D) C state E) A and B

Answer 42

A) L state

Question 43

Regarding the reactions of the citric acid cycle, you might expect the ΔG of reactions in which CO2 is lost to be __________________, the ΔG of reactions utilizing transfer groups from CoA would be ___________________ , and reactions such as isomerizations or hydrations would likely have _______________ ΔG values.

Answer 43

Strongly negative, Strongly negative, Near zero

Question 44

______ is the first compound that is oxidized in the citric acid cycle. Oxaloacetate Malate synthase Malate Malonate Krebs Aconitase Succinyl-CoA synthetase α-ketoglutarate Carbon dioxide Malate dehydrogenase Isocitrate Succinate dehydrogenase

Answer 44

Isocitrate

Question 45

______ catalyzes a substrate-level phosphorylation reaction within the citric acid cycle. Oxaloacetate Malate synthase Malate Malonate Krebs Aconitase Succinyl-CoA synthetase α-ketoglutarate Carbon dioxide Malate dehydrogenase Isocitrate Succinate dehydrogenase

Answer 45

Succinyl-CoA synthetase

Question 46

In the net reaction of the citric acid cycle, what are the reactants? 3 NAD+ + FAD + GDP + Pi + acetyl-CoA 3 NAD+ + FAD + GTP + Pi + acetyl-CoA 3 NAD+ + FADH2 + GDP + Pi + acetyl-CoA 3 NADH + FAD + GDP + Pi + acetyl-CoA

Answer 46

3 NAD+ + FAD + GDP + Pi + acetyl-CoA

Question 47

Ubiquinone is a _____ molecule that serves as a _____ electron carrier; cytochrome c is a _____ molecule that serves as a _____ electron carrier. hydrophobic; 2; hydrophilic; 1 hydrophobic; 1; hydrophilic; 1 hydrophilic; 2; hydrophobic; 2 hydrophilic; 2; hydrophobic; 1 hydrophobic; 1; hydrophilic; 2

Answer 47

hydrophobic; 2; hydrophilic; 1