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PHR 912 > mini exam kt2 > Flashcards

mini exam kt2 Flashcards

1
Q

Which is the substrate and which are the products of
the TCA cycle? How much energy is produced (in ATP
equivalents)?

A
  • Acetyl-CoA is the main substrate. Main products are CO2,
    and -most important- the reduced cofactors (NADH, FADH2)
    and one GTP
  • 12 ATP equivalents per cycle (3 NADH, 1 FADH2, 1 GTP)
    1 NADH → 3 ATPs; 1 FADH2 → 2 ATPs; GTP → 1 ATP
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2
Q

Which enzymes of the TCA cycle provide
energy?

A
  • Isocitrate dehydrogenase (1 NADH)
  • a-Ketoglutarate dehydrogenase (1NADH)
  • Malate dehydrogenase (1 NADH)
  • Succinate dehydrogenase (1 FADH2)
  • Succinyl-CoA synthetase (1 GTP)
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3
Q

The cycle consists of
_________(1) reactions, _______(2) of
them are energy-
providing key
reactions, the others
support these key
reactions

A
  1. eight
  2. five
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4
Q

What are the components of the Electron
Transport Chain (ETC)? What happens at each
of the four electron carrier complexes?

A
  • Complex I to IV; ubiquinone, cytochrome c
  • Complex I: Entrance point for electrons from NADH
  • Complex II: Entrance point for electrons from FADH2
  • Complex III: uptake and pass on of electrons from/to
    movable components of ETC: uptake from ubiquinone;
    pass on to cytochrome C
  • Complex IV: electrons are taken from cytochrome c and
    are passed on to molecular oxygen
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5
Q

Why is ubiquinone called ubiquinone? Why is it
also named Co-enzyme Q10? How is it called after
take up of electrons and protons?

A

-ubiquinone is ubiquitious (= you find it in every
organism!)
Even obligatory anaerobic bacteria have it in their ETC. Complex
IV of the ETCs of anaerobes places the electrons on sulfur or
carbon instead of on oxygen!
- Q10 refers on the isoprene side chain consisting of 10
isoprene units
- Dihydroquinone (Co-enzyme QH2)

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6
Q

Why do Fe-complexes in the ETC have different
environments?

A

To modify (or fine-tune) their redox potential

  • In Complex I are various FeS (iron sulfur) complexes for modification (= fine
    tuning) of the Fe2+/Fe3+ redox potential. There is H+-transport (from matrix to
    intermembrane space)
  • In Complex II are various FeS (iron sulfur) complexes for modification (= fine
    tuning) of the Fe2+/Fe3+ redox potential. This is also part of the TCA cycle.
    There is no H+-transport associated with this carrier complex.
  • In Complex III are both, FeS complexes and heme-iron complexes (=
    cytochromes). There is H+-transport (from matrix to intermembrane space)
  • In Complex IV are both, copper complexes (modifying Cu1+/Cu2+ redox
    potential) and cytochromes (modifying Fe2+/Fe3+ potential). The cooperation
    of a heme-iron and a copper complex enables the splitting and reduction of
    O2 into 2 H2O). There is H+-transport (from matrix to intermembrane space).
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7
Q

There are _____ (1)
alternative
entrance points. what are they (complexes)

A
  1. two

-either complex I or
complex II.

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8
Q

What are the two components of protonmotive
force that drives the ATP-Synthases? Which
way do the protons flow for ATP synthesis?

A

The proton gradient (H+ or pH) between intermembrane space and
matrix, built up during the ETC process, where at three points protons are
channeled out from the matrix into the intermembrane space.
This also leads to an electrochemical potential (V). Both together is called
the chemiosmotic theory!
For ATP synthesis, the protons are channeled through the ATPase from
the intermembrane space to the matrix.

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9
Q

The energy for ATP synthesis arises from an _______
across the inner mitochondrial membrane

A

H+ -gradient

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10
Q

The _____ ________ us impermeable to protons

A

inner membrane

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11
Q

Due to the out-transport of protons by
the ______ ___________ ________, a H+-
gradient (pH) builds up

A

the electron transport chain

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12
Q

the _____ _______ (1) causes a ________ _______ _____(2)

A
  1. proton gradient
  2. transmembrane electrochemical potential
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13
Q

Both pH and V are the driving force
(protonmotive force) to bring the protons
back into the matrix. This process
delivers the energy to _______ ______(1)

A
  1. synthesize atp
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14
Q

What are the components of the ATP-Synthase?
What happens where?

A
  • In the F0 half of the ATPase, located in the inner mitochondrial membrane, are
    the proton channel a, which turns the “wheel” c.
  • The F1 half of the ATPase is reaching into the matrix: It is composed of the
    gamma-axle (which connects the “wheel” c with the ATP synthesis site,
    consisting of the three alpha- and three beta subunits. The gamma-axle is
    driven by the “wheel” c, and steers the ATP-synthesizing beta-units through the
    O (open), L (loose) and T (tight) stages of ATP synthesis.
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15
Q

atp synthase comprises a ______ ____ (1) and ______ ____(2)

A
  1. proton channel (F0)
  2. ATPase site (F1)
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16
Q

Why is dinitrophenol (or other lipophilic phenolic
compounds with a pKA ~ 7) dangerous?

A
  • Dinitrophenol (DNP) is a lipophilic phenol with a pKa ~ 7. Such
    penolic compounds are toxins. The process is unwanted, since it
    prevents ATP synthesis.
  • In contrast, uncoupling by thermogenin, a heat generator in brown
    adipose tissue, is a wanted process, since heat is needed (e.g., in
    young babies, who have not yet learned to shiver).
17
Q

Uncoupling of Electron Transport Chain and ATP-
Synthase

A

unwanted, through chemical ‘uncouplers’ such as DNP (dinitrophenol)

  • lipophilic compounds with a pKa ~ 7
  • no ATP is synthesized, rapid oxidation of NADH/H+ and FADH2, heat release
18
Q

What is thermogenin, and where do you find it?

A

Thermogenin is a transmembrane protein located in the inner
mitochondrial membrane of brown adipose cells. It is a heat
generator.

  • It uncouples the electron transport chain from the ATP-Synthase by
    pumping protons from the intermembrane space into the matrix
  • The energy normally used for the ATP synthesis is released as heat
    This is a wanted process when heat is needed (e.g., in young
    babies, who have not yet learned to shiver).
  • The potential conversion of white (no thermogenin) into brown
    (thermogenin!) adipose is studied in context with the drug sildenafil
    (better known as Viagra), which may have a future as anti-obesity drug,
    since brown adipose is a calorie burner!
19
Q

a thermogenin (heat generator) is a transmembrane protein is located in the ______ _____ (1)
membrane of _______ ________ _____ (2)

A
  1. inner mitochondrial
  2. brown adipose cells
20
Q

Thermogenin (heat generator) does what?

A

uncouples the electron transport chain from the ATP-Synthase by
pumping protons from the intermembrane space into the matrix

21
Q

the energy normally used for the ATP synthesis is released as _____-

A

heat

22
Q

Which of the following coenzymes is unique to -keto
acid dehydrogenase complexes?
A. NAD
B. FAD
C. GDP
D. H2O
E. Lipoic acid

A

E. Lipoic acid

23
Q

A patient diagnosed with thiamine deficiency exhibited
fatigue and muscle cramps. The muscle cramps have been
related to an accumulation of metabolic acids. Which of
the following metabolic acids is most likely to accumulate
in a thiamine deficiency?
A. Isocitric acid
B. Pyruvic acid
C. Succinic acid
D. Malic acid
E. Oxaloacetic acid

A

B. Pyruvic acid

24
Q

Succinate dehydrogenase differs from all other enzymes in
the TCA cycle in that it is the only enzyme that displays
which of the following characteristics?
A. It is embedded in the inner mitochondrial membrane.
B. It is inhibited by NADH.
C. It contains bound FAD.
D. It contains Fe–S centers.
E. It is regulated by a kinase

A

A. It is embedded in the inner mitochondrial membrane.

25
Q

During exercise, stimulation of the TCA cycle results
principally from which of the following?
A. Allosteric activation of isocitrate dehydrogenase by
increased NADH
B. Allosteric activation of fumarase by increased ADP
C. A rapid decrease in the concentration of four-carbon
intermediates
D. Product inhibition of citrate synthase
E. Stimulation of the flux through a number of enzymes
by a decreased NADH/NAD ratio

A

E. Stimulation of the flux through a number of enzymes
by a decreased NADH/NAD ratio

26
Q

Coenzyme A is synthesized from which of the following
vitamins?
A. Niacin
B. Riboflavin
C. Vitamin A
D. Pantothenate
E. Vitamin C

A

D. Pantothenate

27
Q

An individual displays lactic acidemia as well as a reduced activity of a-ketoglutarate dehydrogenase activity. the most likely single enzymatic mutation that leads to these changes would be in which one of the following proteins

a. the e3 subunit of pyruvate dehydrogenase
b. the e1 subunit of pyruvate dehydrogenase
c. the e2 subunit of pyruvate dehydrogenase
d. lactate dehydrogenase
e. pyruvate carboxylase

A

a. the e3 subunit of pyruvate dehydrogenase

28
Q

a patient diagnosed with thiamin deficiency exhibited fatigue and muscle cramps. the muscle cramps have been related to an accumulation of metabolic acids. which one of the following metabolic acid is most likely to accumulate in a thiamin deficiency?

a. isocritic acid
b. pyruvic acid
c. succinic acid
d. malic acid
e. oxaloacetic acid

A

b. pyruvic acid

29
Q

succinate dehydrogenase differs from all the other enzymes in the TCA cycle in that it is the only enzyme that displays which one of the following characteristics?

a. it is embedded in the inner mitochondrial membrane
b. it is inhibited by NADH
c. it contains bound FAD
d. it contains Fe-S centers
e. it is regulated by a kinase

A

a. it is embedded in the inner mitochondrial membrane

29
Q

during exercise stimulation of the TCA cycle results principally form which one of the following?

a. allosteric activation of isocitrate dehydrogenase by increased NADH
b. allosteric activation of fumarase by increased ADP
c. a rapid decrease in the concentration of four-carbon intermediates
d. product inhibition of citrate synthase
e. stimulation of the flux through several enzymes by a decreased NADH/NAD+ ratio

A

e. stimulation of the flux through several enzymes by a decreased NADH/NAD+ ratio

30
Q

a deficiency in which one fhte following compounds would lead to an inability to produce coenzyme A?

a. niacin
b. riboflavin
c. vitamin a
d. pantothenate
e. vitamin c

A

d. pantothenate

31
Q

one of the major roles of the TCA cycle is to generate reduced cofactors for ATP production from oxidative phosphorylation. the compound donating the net eight electrons to the cofactors is which one of the following?

a. pyruvate
b. acetyl-CoA
c. lactate
d. oxaloacetate
e. phosphoenolpyruvate

A

b. acetyl-CoA

32
Q

atherosclerosis can narrow the coronary arteries, leading to decreased blood flow and hypoxia of cardiac cells (cardiomyocytes). this causes the patient to experience angina. which one of the following is likely to occur in the cardiomyocytes during the hypoxic event?

a. the TCA cycle in the cytosol is greatly impaired
b. pyruvate oxidation is increased
c. lactate cannot be used as a fuel
d. citrate accumulates
e. succinyl-CoA accumulates

A

c. lactate cannot be used as a fuel

33
Q

a distance runner is training for her half marathon and as part of the training is allowing her muscles to use fatty acids as a fuel source. fatty acids are converted to acetyl-CoA in the mitochondria, at which point the acetyl-CoA can be oxidized in the TCA cycle to generate reduced cofactors. which one of the following correctly describes how the acetyl-CoA is metabolized in the mitochondria?

a. one molecule of acetyl-CoA produces two molecules of CO2, three molecules of NADH, and one molecule of FAD(2H) and one molecule of ATP
b. all of the energy for high-energy phosphate bonds in derived from oxidative phosphorylation
c. NAD+ is the only electron acceptor in the cycle
d. substrate-level phosphorylation generates one high-energy phosphate bond during the cycle.
e. the TCA cycle requires large amounts of vitamins c and d as coenzymes.

A

d. substrate-level phosphorylation generates one high-energy phosphate bond during the cycle.

34
Q

at birth, a full term male neonate was found to be severely acidotic. his condition was found to result from an X-linked dominant mutation of the a-subunit of e1 in the PDC. compared with a healthy neonate in the same dietary state, what would be the consequences of this mutation?

a. an increase in plasma concentrations of lactate and pyruvate
b. a higher ATP/ADP ratio in cells of the brain
c. a decrease in the rate of glycolysis in brain cells
d. an increase in the activity of the electron-transfer chain in brain cells
e. an increase in plasma acetyl-CoA levels

A

a. an increase in plasma concentrations of lactate and pyruvate

35
Q

a pyruvate carboxylase deficiency will lead to lactic acidemia because of which one of the following?

a. an accumulation of acetyl-CoA in the mitochondria
b. allosteric activation of lactate dehydrogenase
c. an accumulation of NADH in the mitochondrial matrix
d. allosteric activation of the PDC
e. an accumulation of ATP in the matrix

A

a. an accumulation of acetyl-CoA in the mitochondria

PHR 912 (2 decks)

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