Biochem Chapter 17

Which one of the following would not be involved in the equation that describes the oxidative decarboxylation of pyruvate?
HS-CoA
NAD+
ATP
CO2
NADH

ATP

Which reaction of the citric acid cycle is most similar to the reaction catalyzed by the pyruvate dehydrogenase complex?
alpha-ketoglutarate to succinyl-CoA.
fumarate to malate.
malate to oxaloacetate.
succinyl-CoA to succinate.
citrate to isocitrate

alpha-ketoglutarate to succinyl-CoA.

Which of the following are products of the reaction catalyzed by pyruvate dehydrogenase?
i) CO2
ii) NADH
iii) acetyl-CoA
iv) phosphoenolpyruvate
products i) and iii)
product iv)
product i), ii), iii) and iv)
products i), ii) and iii)
products ii) and iv)

products i), ii) and iii)

Which of the following statements is TRUE regarding the oxidative decarboxylation of pyruvate?
It occurs in the inner mitochondrial membrane.
In skeletal muscle, calcium ions inhibit the pyruvate dehydrogenase complex.
One of the products of this reaction

One of the products of this reaction is a molecule containing a thioester bond.

Assume that pyruvate is completely catabolized under aerobic conditions to CO2 and H2O. What is the net yield of ATP that can be expected from this? Assume that re-oxidation of NADH via the electron transport chain yields the equivalent of 3 ATP, and that

15 ATP

Which of the following are involved in the equation that best describes the oxidative decarboxylation of pyruvate?
i. ATP
ii. HS-CoA
iii. H20
iv. NAD+
v. CO2
vi. Oxaloacetate
ii, iv and v
i, v and vi
ii and v
i, ii, iv and vi
iii, iv and v

ii, iv and v

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. -Ketoglutarate dehydrogenase.
i, iii, and iv
i, ii, and iv
i and iv

i and iv

Which of the following statements about the pyruvate dehydrogenase complex and the -ketoglutarate dehydrogenase complex is FALSE?
Their rates are both increased when the NAD+/NADH ratio in the cell is high.
The products of the reactions catalysed by both

Both complexes are inhibited by the high energy thioester acetyl-CoA.

How many ATP equivalents are made from the complete aerobic catabolism of succinyl-CoA? Assume that re-oxidation of NADH via the electron transport chain yields the equivalent of 3 ATP, and that re-oxidation of FADH2 yields 2 ATP.
6 ATP
5 ATP
9 ATP
12 ATP

6 ATP

Which of the following is required for the conversion of succinate to fumarate in the citric acid cycle?
GDP
FAD
QH2
NAD+

FAD

Which of the following are involved in the equation that best describes the oxidative decarboxylation of -ketoglutarate?
1) ATP
2) HS-CoA
3) H20
4) NAD+
5) CO2
6) Succinate
3, 4 and 5
2 and 5
1, 2, 4 and 6
1, 5 and 6
2, 4 and 5

2, 4 and 5

Which of the following enzymes does not catalyze a regulated reaction?
Pyruvate carboxylase.
Pyruvate kinase.
Succinate dehydrogenase.
alpha-Ketoglutarate dehydrogenase.
Isocitrate dehydrogenase.

Succinate dehydrogenase.

Which reaction of the citric acid cycle produces a nucleoside triphosphate?
malate to oxaloacetate
citrate to isocitrate
succinyl-CoA to succinate
succinate to fumarate
fumarate to malate

succinyl-CoA to succinate

Which of the following statements about the oxidative decarboxylation of pyruvate is TRUE?
One of the products of this reaction is a molecule containing a thioester bond.
The process occurs in the cytosol.
The reaction is so important to aerobic catabolis

One of the products of this reaction is a molecule containing a thioester bond.

Which reaction or reactions in the scheme of glycolysis and the citric acid cycle attached at the back of this exam will NOT proceed in the absence of inorganic phosphate ions?
1 and 3
7
8 and 11
12 and 16

7

Which of the following compounds are used in a substrate-level phosphorylation reaction?
i) 1,3-bisphosphoglycerate
ii) glucose-6-phosphate
iii) phosphoenolpyruvate
iv) 3-phosphoglycerate
v) succinyl-CoA
i) and iii)
ii) and iv)
ii), iv), and v)
i), iii),

i), iii), and v)

Another name for the citric acid cycle is the ______.
malate synthase
-ketoglutarate
carbon dioxide
oxaloacetate
malate dehydrogenase
malonate
succinyl-CoA synthetase
isocitrate
malate
Krebs cycle
aconitase
succinate dehydrogenase

Krebs cycle

______ is the first compound that is oxidized in the citric acid cycle.
Krebs cycle
malate
succinate dehydrogenase
aconitase
oxaloacetate
succinyl-CoA synthetase
alpha-ketoglutarate
malate dehydrogenase
carbon dioxide
isocitrate
malate synthase
malonate

isocitrate

______ is an enzyme that catalyzes a substrate-level phosphorylation
succinate dehydrogenase
isocitrate
Krebs cycle
malonate
malate synthase
succinyl-CoA synthetase
oxaloacetate
malate dehydrogenase
malate
aconitase
alpha-ketoglutarate
carbon dioxide

succinyl-CoA synthetase

The citric acid cycle intermediate ______ is found at the beginning and at the end of the citric acid cycle.
succinate dehydrogenase
carbon dioxide
oxaloacetate
malate synthase
malate
malonate
aconitase
succinyl-CoA synthetase
Krebs cycle
alpha-ketoglutar

oxaloacetate

The only membrane-bound enzyme of the citric acid cycle is ______.
malate dehydrogenase
malate
aconitase
-ketoglutarate
carbon dioxide
succinyl-CoA synthetase
isocitrate
succinate dehydrogenase
oxaloacetate
Krebs cycle
malate synthase
malonate

succinate dehydrogenase

The enzyme ______ contains an iron-sulfur cluster.
isocitrate
-ketoglutarate
succinate dehydrogenase
succinyl-CoA synthetase
carbon dioxide
aconitase
malate dehydrogenase
malate
oxaloacetate
malate synthase
malonate
Krebs cycle

aconitase

The compound ______ is a competitive inhibitor of succinate dehydrogenase.
malate synthase
malate dehydrogenase
aconitase
succinate dehydrogenase
succinyl-CoA synthetase
malonate
-ketoglutarate
oxaloacetate
malate
carbon dioxide
Krebs cycle
isocitrate

malonate

Which of the following coenzymes is required by E1 of the pyruvate dehydrogenase complex or catalytic activity?
FAD
NAD+
thiamine pyrophosphate
lipoic acid
biotin

thiamine pyrophosphate

E2 of the pyruvate dehydrogenase complex contains a lipoyl group that is covalently attached to a ______ residue of the enzyme?
lysine
histidine
arginine
glutamate
serine

lysine

Which of the following is an intermediate between citrate and isocitrate in the citric acid cycle?
carboxybiotin
succinyl-phosphate
cis-aconitate
hydroxyethyl-TPP
oxalosuccinate

cis-aconitate

During the oxidation of isocitrate, the intermediate that is decarboxylated to form -ketoglutarate is ______.
carboxybiotin
succinyl-phosphate
oxalosuccinate
cis-aconitate
hydroxyethyl-TPP

oxalosuccinate

Which of the following enzymes of the citric acid cycle contains an FAD prosthetic group?
malate dehydrogenase
isocitrate dehydrogenase
-ketoglutarate dehydrogenase
succinate dehydrogenase
succinyl-CoA synthetase

succinate dehydrogenase

In which of the following locations do eukaryotes house the enzymes of the citric acid cycle?
Golgi apparatus
endoplasmic reticulum
outer mitochondrial membrane
cytosol
mitochondrial matrix

mitochondrial matrix

Which of the following is the metabolic intermediate that condenses with oxaloacetate to form citrate?
succinyl-phosphate
acetyl-CoA
cis-aconitate
carboxybiotin
oxalosuccinate

acetyl-CoA

How many NADH are produced when one acetyl group is oxidized in the citric acid cycle?
1
2
3
4
more than 4

3

Which of the following serves as a "swinging arm" when it transfers a reaction intermediate from one active site to the next?
Thiamine pyrophosphate
Coenzyme A
FAD
Lipoamide
NAD+

Lipoamide

Which of the following coenzymes is NOT used by the pyruvate dehydrogenase complex?
NAD+
coenenzyme A
FAD
thiamine pyrophosphate
pyridoxal phosphate

pyridoxal phosphate

Which of the following amino acids participates in the transfer of a phosphate group in the reaction catalyzed by succinyl-CoA synthetase?
glutamate
lysine
histidine
aspartate
serine

histidine

Consider the following reaction which has a ?G�' ? +30 kJ/mol.
malate + NAD+ oxaloacetate + NADH + H+
In muscle cells, the reaction proceeds as written, i.e., from left to right. How can this occur?
The enzyme can only catalyze the reaction in that direct

The concentration of malate must be higher than oxaloacetate for this reaction to occur in the cell.

How many electrons are transferred from one acetyl group when it is converted to two carbon dioxide molecules in the citric acid cycle?
8
6
10
2
4

8

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

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

In the net reaction of the citric acid cycle, what are the products?
3 NADH + FAD + GTP + 2CO2 + CoA
3 NAD+ + FADH2 + GTP + 2CO2 + acetyl-CoA
3 NADH + FAD + GDP + 2CO2 + CoA
3 NADH + FADH2 + GTP + 2CO2 + CoA

3 NADH + FADH2 + GTP + 2CO2 + CoA

In pyruvate dehydrogenase, which cofactor is used to decarboxylate pyruvate?
CoA
Lipoic acid
FAD
Thiamine pyrophosphate (TPP)

Thiamine pyrophosphate (TPP)

Which cofactor of pyruvate dehydrogenase contains a sulfhydryl group?
CoA
NAD+
FAD
Thiamine pyrophosphate (TPP)

CoA

Which enzyme of the citric acid cycle is strongly inhibited by malonate?
Fumarase
Succinyl-CoA synthetase
Citrate synthase
Succinate dehydrogenase

Succinate dehydrogenase

Which enzyme of the citric acid cycle is very similar structurally and mechanistically to lactate dehydrogenase and alcohol dehydrogenase?
NAD+ -dependent isocitrate dehydrogenase
Malate dehydrogenase
-Ketoglutarate dehydrogenase
Succinate dehydrogenase

Malate dehydrogenase

Under standard state conditions, which enzyme of the citric acid cycle has the largest positive ?G0'?
Isocitrate dehydrogenase
Malate dehydrogenase
Aconitase
Citrate synthase

Malate dehydrogenase

Which three of the following are possible sources for acetyl-CoA that enters the citric acid cycle?
1) oxidative decarboxylation of pyruvate
2) ? oxidation of fatty acids
3) catabolism of certain amino acids
4) citrate
5) carboxylation of pyruvate
1, 2 an

1, 2 and 3

Which of the following is FALSE with respect to the pyruvate dehydrogenase complex?
It is located in the mitochondrial matrix.
The proximity of the catalytic enzymes in the cluster slows down the overall rate.
It is a multienzyme complex.
It is activated

The proximity of the catalytic enzymes in the cluster slows down the overall rate.

Why is the citric acid cycle considered to be part of aerobic metabolism even though oxygen does not explicitly appear in any reaction?
Because it takes place in the mitochondrion.
Because it produces reduced electron carriers, which are re-oxidized by tr

Because it produces reduced electron carriers, which are re-oxidized by transferring their electrons ultimately to oxygen.

Consider the reactions of the citric acid cycle in the figure. At which steps are carbon atoms added to or removed from the reactants?
12, 13 and 14
12, 14 and 15
12, 15 and 19
12, 14 and 19

12, 14 and 15

Which of the following statements is FALSE regarding regulation of the pyruvate dehydrogenase complex?
A. Calcium ions inhibit the complex.
B. A high ratio of NADH/NAD+ inhibits the complex.
C. Acetyl-CoA inhibits the complex.
A and B

A. Calcium ions inhibit the complex.

Which of the following statements about NADH is FALSE?
The oxidation of one molecule of NADH by the electron transport chain forms one molecule of water.
NAD+ is converted to NADH by -ketoglutarate dehydrogenase.
NAD+ is converted to NADH by isocitrate de

NADH is an allosteric activator of pyruvate dehydrogenase.

Which of the following statements is/are TRUE regarding acetyl-CoA?
A. Acetyl-CoA activates pyruvate dehydrogenase.
B. Acetyl-CoA is considered a "high-energy" molecule because of its phosphoester bond.
C. Acetyl-CoA activates pyruvate carboxylase.
D. Ace

C. Acetyl-CoA activates pyruvate carboxylase.

Which of the following statements is TRUE regarding the citric acid cycle?
Ca2+ inhibits -ketoglutarate dehydrogenase by activating a protein kinase.
The pyruvate dehydrogenase complex controls the rate of entry of fats into the citric acid cycle.
In euka

The rate of the citric acid cycle increases when the NADH/NAD+ ratio is low

The rate of the citric acid cycle would be INCREASED under which of the following conditions?
A. The ADP/ATP ratio is high.
B. The ADP/ATP ratio is low.
C. The NAD+/NADH ratio is low.
D. The concentration of oxaloacetate is low.
B and C

A. The ADP/ATP ratio is high.

Anapleurotic reactions are essential to the functioning of the citric acid cycle. Which of the following enzymes catalyzes such a reaction?
Malate dehydrogenase
Pyruvate carboxylase
Glyceraldehyde-3-phosphate dehydrogenase
Citrate synthase

Pyruvate carboxylase

Under which of the following conditions is the entry of acetyl-CoA into the citric acid cycle DECREASED?
When the NADH/NAD+ ratio is high.
When ADP levels are elevated.
When NADH is rapidly oxidized via the electron transport system.
When NAD+ levels are

When the NADH/NAD+ ratio is high.

The enzyme ______ is part of the glyoxylate cycle.
malate dehydrogenase
succinate dehydrogenase
oxaloacetate
malate synthase
aconitase
malate
malonate
isocitrate
-ketoglutarate
Krebs cycle
succinyl-CoA synthetase
carbon dioxide

malate synthase

Which of the following terms describes the citric acid cycle is referred to as being both catabolic and anabolic?
amphipathic
cataplerotic
anaplerotic
amphibolic

amphibolic

The reaction that is catalyzed by pyruvate carboxylase is an example of an ______ reaction because it replenishes the citric acid cycle intermediates that have been siphoned off for biosynthesis.
amphibolic
anaplerotic
cataplerotic
amphipathic

anaplerotic

Which of the following causes pyruvate dehydrogenase kinase to catalyze the phosphorylation and inactivation of E1 in the pyruvate dehydrogenase complex?
Ca2+
elevated concentrations of NAD+ and ADP
elevated concentrations of acetyl-CoA
insulin
elevated c

elevated concentrations of acetyl-CoA

Which of the following best describes the citric acid cycle as a central pathway of metabolism?
A. It is important for recovery of energy from carbohydrates only.
B. It is important for recovery of energy from fatty acids only.
C. It is important for reco

D. It is important for recovery of energy from several metabolic fuels that are broken down to acetyl-CoA.

Which of the following enzymes catalyzes a reaction with the pictured compound as an intermediate?
malate dehydrogenase
succinyl-CoA synthetase
fumarase
succinate dehydrogenase
-ketoglutarate dehydrogenase

succinyl-CoA synthetase

Which of the following can be said about the isocitrate product of aconitase?
The product always has the S configuration.
The product always has the R configuration.
The product can have either the R or S configuration
The product isn't chiral, so has nei

The product always has the R configuration.

Which of the following enzymes of the citric acid cycle is inhibited by ATP?
succinyl-CoA synthetase
malate dehydrogenase
citrate synthase
isocitrate dehydrogenase
-ketoglutarate dehydrogenase

isocitrate dehydrogenase

Which enzyme has an intermediate of the form presented? (TPP = thiamine pyrophosphate)
pyruvate decarboxylase
enolase
glyceraldehyde-3-phosphate dehydrogenase
aldolase
lactate dehydrogenase

pyruvate decarboxylase

Which of the following citric acid cycle intermediates can be converted to aspartate via transamination?
citrate
alpha-ketoglutarate
succinate
fumarate
oxaloacetate

oxaloacetate

How is flux throught the citric acid cycle controlled?
Primarily by control of citrate synthase
Primarily by control of isocitrate dehydrogenase
Primarily by control of alpha-ketoglutarate dehydrogenase
At many points, including all of the above.

At many points, including all of the above.

What compounds are produced when oxaloacetate undergoes transamination with alanine?
Aspartate and alpha-ketoglutarate
Aspartate and pyruvate
Glutamate and pyruvate
Glutamate and alpha-ketoglutarate

Aspartate and pyruvate