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fifth 50 Flashcards

1
Q

Which molecule in the net reaction of the citrate cycle contributes to the inhibition of pyruvate dehydrogenase?

FAD

H2O

H+

NADH

A

NADH

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2
Q

The poison compound 1080 converts fluoroacetate to fluorocitrate. Which enzyme in the citrate cycle is inhibited by this poison?

aconitase

citrate synthase

isocitrate dehydrogenase

a-ketoglutarate dehydrogenase

A

aconitase

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3
Q

Calculate the delta E of a coupled redox reaction with O2 and ferredoxin (Fe2+) using the table below.

−1.25

−0.39

  1. 39
  2. 25
A

1.25

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4
Q

Identify the strongest oxidant in the table below.

O2

oxaloacetate

pyruvate

ferredoxin

A

O2

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5
Q

Identify the strongest reductant in the table below.

O2

oxaloacetate

pyruvate

ferredoxin

A

ferredoxin

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6
Q

Coenzyme A is derived from which of the following vitamins?

thiamine

pantothenic acid

riboflavin

niacin

A

pantothenic acid

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7
Q

Which vitamin is the precursor to the coenzyme that functions as a reductant in the pyruvate dehydrogenase complex in the final step of the reaction?

thiamine

pantothenic acid

riboflavin

niacin

A

riboflavin

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8
Q

The disease beriberi is a result of which vitamin deficiency?

thiamine

pantothenic acid

riboflavin

niacin

A

thiamine

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9
Q

Classify the reaction that occurs at step 1 in the reaction schematic of the pyruvate dehydrogenase reaction below.

isomerization

addition

oxidation reduction

decarboxylation

A

decarboxylation

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10
Q

Identify the E1 subunit in the reaction schematic of the pyruvate dehydrogenase reaction below.

pyruvate dehydrogenase

dihydrolipoyl dehydrogenase

dihydrolipopyl acetyltransferase

flavin adenine dinucleotide

A

pyruvate dehydrogenase

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11
Q

A patient seeks medical attention for ulcerous skin lesions. The patient is diagnosed with

arsenic exposure.

a deficiency in vitamin B3.

beriberi.

cheilosis.

A

arsenic exposure.

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12
Q

If acetyl-CoA is not metabolized by the citrate cycle, the molecule in the cell

undergoes fatty acid metabolism.

is transported across the cell membrane.

is used to synthesize amino acids.

is used during glycolysis.

A

undergoes fatty acid metabolism.

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13
Q

How would a high NADH to NAD+ ratio be expected to affect the pyruvate dehydrogenase reaction?

The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an increase in pyruvate dehydrogenase activity.

The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity.

The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases.

The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.

A

The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity.

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14
Q

How would an increased level of acetyl-CoA be expected to affect the pyruvate dehydrogenase reaction?

The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity.

The last step of the pyruvate dehydrogenase reaction would be blocked, resulting in a decrease in activity.

The E1 subunit would be phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase would decrease.

The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.

A

The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity.

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15
Q

The reaction catalyzed by __________is the most endergonic reaction in the citrate cycle.

fumarase

succinate dehydrogenase

malate dehydrogenase

aconitase

A

malate dehydrogenase

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16
Q

The reaction catalyzed by __________ is likely to be reversible under cellular conditions according to the delta G.

malate dehydrogenase

citrate synthase

succinate dehydrogenase

a-ketoglutarate dehydrogenase

A

succinate dehydrogenase

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17
Q

A high concentration of which molecule would inhibit citrate synthase in the citrate cycle?

AMP

ADP

NAD+

ATP

A

ATP

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18
Q

Which anaplerotic reaction balances the input of oxaloacetate with acetyl-CoA in the citrate cycle by converting pyruvate into oxaloacetate?

pyruvate carboxylase

malate dehydrogenase

malic enzyme

pyruvate kinase

A

pyruvate carboxylase

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19
Q

The anaplerotic reaction catalyzed by pyruvate carboxylase requires which coenzyme?

niacin

biotin

riboflavin

thiamine

A

biotin

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20
Q

Which citrate cycle intermediate is siphoned off the citrate cycle during starvation?

succinyl-CoA

malate

a-ketoglutarate

fumarate

A

malate

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21
Q

Which citrate cycle metabolite is used as a precursor for heme biosynthesis?

succinyl Co-A

oxaloacetate

a-ketoglutarate

malate

A

succinyl Co-A

22
Q

Predict the fate of a-ketoglutarate when it is not used in the citrate cycle.

cholesterol synthesis

heme synthesis

gluconeogenesis

amino acid synthesis

A

amino acid synthesis

23
Q

The ultimate electron acceptor of the mitochondrial electron transport system is

O2.

NADH.

H2O.

cytochrome c.

A

O2

24
Q

Studies of the inner mitochondrial membrane reveal its composition to be approximately 20% lipid bilayer and 80% protein. What is true of these proteins?

Abundant collagen proteins form connective tissues to strengthen the membrane against the pH gradient.

High levels of proteins are required to metabolize glucose in the glycolysis pathway for rapid energy production.

The proteins form highly folded cristae structures.

The proteins are largely electron transport complexes and ATP synthase enzymes.

A

The proteins are largely electron transport complexes and ATP synthase enzymes.

25
Q

As electrons from NADH pass through the electron transport system,

the oxidized form of ADP is reduced to ATP.

the reduction potential of the mitochondria becomes more thermodynamically favorable.

the resulting electron gradient is used to make ATP.

protons are pumped across the mitochondrial membrane to create a pH gradient.

A

protons are pumped across the mitochondrial membrane to create a pH gradient.

26
Q

What is the fate of NADH after it donates its electrons to the electron transport system?

NAD+ is excreted from the cell and sent to the liver for final degradation.

NADH is used for cellular biosynthesis.

NAD+ is re-reduced by the TCA cycle or glycolysis and returns to electron transport system, where the process is repeated.

NAD+ is fed into the TCA cycle for oxidation of CO2.

A

NAD+ is re-reduced by the TCA cycle or glycolysis and returns to electron transport system, where the process is repeated.

27
Q

Use the table below to answer the question.

Standard Reduction Potentials (delta E) for Half Reactions
NAD+ + H+ + 2 e− --> NADH
−0.32 V
FAD + 2 H+ + 2 e− --> FADH2
−0.22 V
O2 + 4 H+ + 4 e− --> 2 H2O
\+0.82 V

In the direction indicated, which of the following reactions are thermodynamically favored?
I. NAD+ + H2O mc227-5.jpg O2 + NADH
II. FADH2 + H2O mc227-6.jpg O2 + FAD
III. NADH + O2 mc227-7.jpg H2O + NAD+

I and II

I and III

I, II, and III

III only

A

III only

28
Q

Which reaction does the concept of oxidative phosphorylation refer to?

O2 + ADP + Pi –> 2 H2O + ATP

NADH + H+ + 1/2 O2 –> NAD+ + H2O

ADP + Pi –> ATP

NADH + 1/2 O2 + H+ + ADP + Pi –> NAD+ + ATP + H2O

A

NADH + 1/2 O2 + H+ + ADP + Pi –> NAD+ + ATP + H2O

29
Q

A decrease in __________ would be LEAST likely to affect the processes of the electron transport system.

oxygen concentrations in the cell

the TCA cycle activity

cellular CO2 concentrations

the concentration of cellular NADH

A

cellular CO2 concentrations

30
Q

Which of the following is NOT a part of oxidative phosphorylation?

NADH is oxidized to NAD+.

O2 is reduced to H2O.

Electrons from O2 are transferred to ATP.

The pumping of protons is coupled with the formation of ATP.

A

Electrons from O2 are transferred to ATP.

31
Q

Which of the following is an electron carrier in the mitochondrial electron transport system?

proton

water

quinone

ATP

A

quinone

32
Q

The electron transport complexes found in the electron transport system

contain multiple electron transfer cofactors that facilitate electron transfer through the complexes.

are bound to the outer mitochondrial membrane.

pump protons from outside the mitochondria to the mitochondrial matrix on electron transfer.

absorb light energy that results in electron transfer.

A

contain multiple electron transfer cofactors that facilitate electron transfer through the complexes.

33
Q

Which one of the following is involved in the flow of electrons from NADH through the electron transport system to molecular oxygen (O2)?

ATP synthase

complex II

complex III

ATP

A

complex III

34
Q

What is the reaction catalyzed by complex III in the electron transport system?

UQH2 + O2 –> UQ + H2O

UQH2 + complex IV+ –> UQ + complex IV

FADH2 + UQ –> FAD + UQH2

UQH2 + cytochrome c+ –> UQ + cytochrome c

A

UQH2 + cytochrome c+ –> UQ + cytochrome c

35
Q

What is the location of the electron transport system protein called cytochrome c?

cytoplasm

mitochondrial matrix

inner mitochondrial membrane

intermembrane space

A

intermembrane space

36
Q

The structure of the electron transport system protein called cytochrome c is highly conserved in nature because the

enzyme has the rare ability to bind O2 and reduce it.

protein active site contains a cofactor unique to the electron transport system.

protein is located inside the mitochondria of eukaryotic cells.

protein plays an important role in the electron transport system and in other critical cellular pathways such as apoptosis.

A

protein plays an important role in the electron transport system and in other critical cellular pathways such as apoptosis.

37
Q

The ATP synthase enzyme contains a central stalk embedded in the mitochondrial membrane. What part of this stalk rotates?

the a3B3 ring

the F1 subunit

the d, h, and OSCP subunits

the ring of c subunits

A

the ring of c subunits

38
Q

ATP synthesis occurs

on the outer mitochondrial membrane.

at the ATP synthase complex after ADP and Pi are transported into the mitochondria.

as a result of the leakage of H+ back out of the mitochondria.

from the electron transfer reactions through complex IV.

A

at the ATP synthase complex after ADP and Pi are transported into the mitochondria.

39
Q

What would happen to a mutated ATP synthase enzyme where the proton binding aspartate residue on the c subunits was mutated to an alanine?

The enzyme would make ATP as normal in the presence of a proton gradient.

The enzyme would not make ATP in the presence of a proton gradient.

The enzyme would make ATP without the need for a proton gradient.

The rotor would rotate in response to a proton gradient, but no ATP would be made.

A

The enzyme would not make ATP in the presence of a proton gradient.

40
Q

Which part of the native ATP synthase enzyme is stationary and does NOT rotate during ATP synthesis?

the rotor

the circle of c subunits

the central y subunit connecting the rotor to the catalytic headpiece

the catalytic headpiece

A

the catalytic headpiece

41
Q

Which one of the following statements about the glycerol phosphate shuttle is true?

It involves the transfer of electrons from cytoplasmic NADH to dihydroxyacetone phosphate (DHAP) to yield glycerol phosphate.

It is more efficient than the malate aspartate shuttle.

NADH produced in the cytoplasm by glycolysis ultimately leads to NADH in mitochondria.

Glycerol phosphate diffuses into the mitochondria.

A

It involves the transfer of electrons from cytoplasmic NADH to dihydroxyacetone phosphate (DHAP) to yield glycerol phosphate.

42
Q

How many ATPs are obtained from one acetyl-CoA run once through the TCA cycle, assuming that all resulting NADH and FADH2 is used by the electron transport chain and oxidative phosphorylation to make ATP?

6.5

9

10

11

A

10

43
Q

If the mitochondrial ATP synthase were inhibited, but the electron transport chain was allowed to run continuously, the pH of the cytoplasm would

decrease.

increase.

remain unchanged.

increase immediately and then decrease.

A

decrease.

44
Q

The drug oligomycin inhibits ATP synthase by preventing protons from flowing through the enzyme. Oligomycin must bind to the __________ of ATP synthase.

catalytic headpiece

F1 subunit

ATP binding site

F0 subunit of

A

F0 subunit of

45
Q

The main activator molecule of the ATP synthesis and the electron transport system is

ATP.

H+.

ADP.

NAD+.

A

ADP.

46
Q

What is the effect of oligomycin, an ATP synthase inhibitor, on the mitochondrial oxidative phosphorylation pathway?

The mitochondria cannot reduce NADH or make ATP.

No proton gradient is formed, and no ATP is synthesized.

Protons leak back into the cytoplasm.

The proton gradient is formed, but no ATP synthesis can occur.

A

The proton gradient is formed, but no ATP synthesis can occur.

47
Q

What happens to patients given the proton gradient uncoupler 2,4-dinitrophenol?

They undergo rapid decrease in body temperature as a result of lack of mitochondrial electron transport.

They experience lower cellular pH as a result of rapid proton gradient dissipation.

Their mitochondrial membranes fail as a result of rapid proton gradient release.

Their body temperatures rise as a result of heat release from gradient uncoupling.

A

They undergo rapid decrease in body temperature as a result of lack of mitochondrial electron transport.

48
Q

What is the cellular location of eukaryotic thermogenin (or uncoupling protein)?

mitochondrial inner membrane

mitochondrial matrix

cytoplasm

both cytoplasm and mitochondrial matrix

A

mitochondrial inner membrane

49
Q

Which animal would have the lowest levels of brown adipose tissue?

newborn human

hibernating squirrel

migrating duck

polar bear

A

migrating duck

50
Q

What is the primary fuel metabolized by the mitochondria in brown adipose tissue of hibernating animals?

glucose

NADH

lipid

ATP

A

lipid

BIOCHEM (7 decks)

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