Discussion chapter 7 Flashcards
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
it plays a role in both catabolism and anabolism
___________________ is the end product of the citric acid cycle’s regeneration phase.
Oxaloacetate.
Select the three citric acid cycle intermediates replenished by anaplerosis in the order they enter the cycle.
- Alpha-Ketoglutarate
2- Succinyl-CoA
3- Oxaloacetate
Which citric acid cycle intermediate is replenished by the following anaplerotic reactions?
1- Carboxylation of pyruvate
2- Transamination of aspartate
3-Transamination of glutamate
1- Oxaloacetate
2-Oxaloacetate
3- Alpha-Ketogluturate
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
15
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
i and iv
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
NADH
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:
- 4H+
- 0
- 4H+
- 2H+
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.
O2 consumption will decrease.
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.
Electron transfer from NADH will stop.
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.
Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur.
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.
It has a membrane-embedded component called F0 and a component found in the matrix referred to as F1.
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
converts a tertiary alcohol that cannot easily be oxidized to a secondary alcohol that can be oxidized
__________________ is the first compound that is oxidized in the citric acid cycle.
Isocitrate
Which of the following enzymes catalyzes a substrate-level phosphorylation?
malate synthase
succinate dehydrogenase
α-ketoglutarate dehydrogenase
succinyl-CoA synthetase
fumarase
succinyl-CoA synthetase
Which reaction below produces GTP in the citric acid cycle?
isocitrate → α-ketoglutarate
α-ketoglutarate → succinyl CoA
succinyl CoA → succinate
fumarate → malate
malate → oxaloacetate
succinyl CoA → succinate
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
an alkane to an alkene
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
a hydration of an alkene
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.
Concentrations of oxaloacetate are kept very low by rapid use in the subsequent step.
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
8
Which of the following is inhibited by high levels of acetyl-CoA?
malate dehydrogenase
succinyl-CoA synthetase
pyruvate carboxylase
pyruvate dehydrogenase
pyruvate dehydrogenase
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
The amount of acetyl CoA produced from carbohydrate metabolism that enters the citric acid cycle would be decreased.
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
I, III
Which of the following can be converted into glutamic acid in a single enzyme-catalyzed step?
isocitrate
oxaloacetate
malate
α-ketoglutarate
succinyl-CoA
α-ketoglutarate
_______________________ and pyruvate can be combined in an ATP-dependent reaction that regenerates one of the key intermediates in the citric acid cycle.
CO2
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
I and II.
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
I, II
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
I, II, IV
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
spontaneously because of the redox potential gradient
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
mitochondrial matrix; cytosol
Complexes I and II each transfer electrons to ___________________.
Ubiquinone or Coenyme Q
For every two electrons transferred from NADH to oxygen, _____ protons are pumped from the matrix to the intermembrane space.
4
6
8
10
12
10
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
Complex II; Complex III
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
NAD+; ubiquinone
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
ubiquinone
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
ubiquinol; cytochrome c
How many protons are moved across the inner mitochondrial membrane at Complex III?
1
2
3
4
none of the above
4
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
one reduced cytochrome c and one semiquinone
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.
4
What is the terminal electron acceptor in aerobic organisms?
NAD+
FAD
ubiquinone
varies from one organism to another
none of the above
none of the above
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.
ATP production would be reduced because of a decrease in the number of protons pumped out of the mitochondrial matrix.
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
A) L state
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.
Strongly negative, Strongly negative, Near zero
______ 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
Isocitrate
______ 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
Succinyl-CoA synthetase
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
3 NAD+ + FAD + GDP + Pi + acetyl-CoA
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
hydrophobic; 2; hydrophilic; 1
