Respiratory chain and oxidative phosphorylations

Q-1. Adenylyl kinase and creatine kinase are found in
a) Outer membrane of mitochondria
b) Inner membrane of mitochondria
c) Inner membrane space
d) Mitochondrial matrix

Answer: Inner membrane space
Explanation:
Outer mitochondrial membrane is permeable to most metabolites. Inner mitochondrial membrane is selectively permeable.
Outer membrane of mitochondria is characterized by the presence of acyl Co-A synthase and glycerophosphate acyl transferase.
Inner membrane of mitochondria is characterized by the presence of cardiolipin, respiratory chain enzyme, ATP synthase and various membrane transporters.
Important point:
Adenylyl kinase and creatine kinase are found in inner membrane space.

Q-2. Enzyme responsible for complete oxidation of glucose to CO2 + H2O is present in
a) Cytosol
b) Mitochondria
c) Endoplasmic reticulum
d) Lysosomes

Answer: Mitochondria
Explanation:
Electron transport system is the final pathway for complete oxidation of glucose to CO2 + H2O.

Q-3. Mitochondria are involved in all of the following except:
a) ATP production
b) Apoptosis
c) Tri-carboxylic acid cycle
d) Fatty acid biosynthesis

Answer: Fatty acid biosynthesis
Explanation:
The biochemical processes taking place in mitochondria:
Respiratory chain
TCA or Kreb’s cycle
Fatty acid oxidation
Formation of acetyl Co-A
Part of urea cycle
Part of gluconeogenesis
Important point:
The main pathway for de novo synthesis of fatty acid occurs in the cytosol.

Q-4. Which of following does not occur in mitochondria? (AIIMS NOV 2016)
a) Beta-oxidation
b) DNA synthesis
c) Fatty acid synthesis
d) Protein synthesis

Answer: Fatty acid synthesis
Explanation:
EMP Pathway or Glycolysis- Cytosol
HMP Shunt- Cytosol
Fatty acid synthesis- Cytosol
Kreb’s cycle- Mitochondria
Electron transport Chain- Mitochondria
Fatty acid oxidation- Mitochondria

Q-5. Final electron goes to In ETC
a) 02
b) Cytochrome a
c) Cytochrome b1
d) FADH2

Answer: O2
Explanation:
The most common of final electron acceptors is molecular oxygen, O2, which combines with the spent electrons of cellular respiration, along with protons, to generate what is known as metabolic water.

Q-6. ETC complex contain Co-Q except
a) Complex I
b) Complex II
c) Complex III
d) Complex VI

Answer: Complex VI
Explanation:
Respiratory chain:
Complex I: NADH-Q Oxido-reductase
Complex II: Succinate Q Reductase
Complex III: Q-Cytochrome c oxido-reductase
Complex IV: Cytochrome c Oxido-reductase
Important point:
Co-Q is called ubiquinone.
Co-Q and cytochrome c oxidase are mobile. Q diffuses rapidly within the membrane while cytochrome c is a soluble protein.

Q-7. Flavo-proteins are important component of ETC
a) Complex-I
b) Complex-II
c) Complex-III
d) Complex-IV

Answer: a and b
Explanation:
Flavo-proteins are important component of complex-I and II.
Iron sulfur proteins (Non-heme iron proteins, Fe-S) are found in complexes- I, II, and III.

Q-8. Iron sulfur proteins (Non-heme iron proteins, Fe-S) are found in all except
a) Complex-I
b) Complex-II
c) Complex-III
d) Complex-IV

Answer: Complex-IV
Explanation:
Flavo-proteins are important component of complex-I and II.
Iron sulfur proteins (Non-heme iron proteins, Fe-S) are found in complexes- I, II, and III.

Q-9. Which component of ETC transfers four protons?
a) NADH-Q Oxido-reductase
b) Cytochrome c Oxido-reductase
c) Q-Cytochrome c oxido-reductase
d) Iso-citrate Dehydrogenase

Answer: a and c
Explanation:
Respiratory chain:
Complex I: NADH-Q Oxido-reductase
Complex II: Succinate Q Reductase
Complex III: Q-Cytochrome c oxido-reductase
Complex IV: Cytochrome c Oxido-reductase
Important points:
Complex I, III and IV act as proton pump creating a proton gradient across the membrane.
Complex I and III pump four H+ and Complex IV pumps two across the membrane in inter-membrane space.

Q-10. Q accepts electrons from all except
a) Complex-I
b) Complex-II
c) Complex-III
d) Acyl Co-A

Answer: Complex-III
Explanation:
Q accepts electrons via complex-I and complex-II.
Important point:
Glycerol-3-Phaosphate and acyl Co-A also pass electrons to Co-Q via different pathways involving flavo-proteins.

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Q-11. In oxidative phosphorylation, the ATP production and respiratory chain are linked by
a) Chemical methods
b) Physical methods
c) Chemi-osmotic methods
d) Conformational changes

Answer: Chemi-osmotic methods
Explanation:
The flow of electrons through respiratory chain generates ATP by process of oxidative phosphorylation.
The chemi-osmotic theory proposed by Peter Mitchell, postulates that ATP production and respiratory chain are coupled by proton gradient across inner mitochondrial membrane so that the proton motive force caused by the electro-potential difference drives the mechanism of ATP synthesis.
Important point:
Complex I, III and IV act as proto pump creating a proton gradient across the membrane.

Q-12. True about ATP synthase is all except
a) One rotation produces 3 ATP
b) F0 unit functions as proton channel
c) Alpha and beta subunits rotate
d) None

Answer: Alpha and beta subunits rotate
Explanation:
The proton motive force drives a membrane located ATP synthase that in presence of Pi and ADP forms ATP. ATP synthase is embedded in the inner membrane.
Several subunits of the protein form a ball like shape arranged around an axis known as F1, which project in the matrix and contains the phosphorylation mechanism.
F1 is attached to membrane protein complex known as F0 spans the membrane and form a proton channel. Flow of proton through F0 caused it to rotate, driving the production of ATP in the F1 complex. Binding change mechanism alters conformation of beta subunits in F1.
Important points:
Complex I and III pump four H+ and Complex IV pumps two across the membrane in inter-membrane space.

Q-13. In oxidative phosphorylation, oxidation of one NADP to NAD+ produces how many ATPs?
a) 3
b) 4
c) 5
d) 6

Answer: 3
Explanation:
Substrate level phosphorylation:
There is a net direct capture of two high energy phosphate groups in glycolytic reaction.
Two more high energy phosphates per mole of glucose are captured in the citric acid cycle during the conversion of succinyl Co-A to succinate.
Oxidative phosphorylation:
NADH produces 3 ATP during the electron transport chain with oxidative phosphorylation because NADH gives up its electron to Complex I, which is at a higher energy level than the other Complexes.
FADH2 produces 2 ATP during the electron transport chain because it gives up its electron to Complex II, bypassing Complex I.

Q-14. The type of enzyme inhibition in which succinate dehydrogenase reaction is inhibited by malonate is an example of:
a) Noncompetitive
b) Uncompetitive
c) Competitive
d) Allosteric

Answer: Competitive
Explanation:
Inhibitors of respiratory chain:
Amytal or Amobarbital and Rotenone inhibit electron transport via Complex-I by blocking the transfer from Fe-S to Co-Q
Antimycin-A, Dimercaprol (BAL) inhibit respiratory chain at Complex-III.
H2S, Carbon monoxide and cyanide inhibit Complex-IV.
Important point:
Malonate is a competitive inhibitor of Complex II.

Q-15. Cellular oxidation is inhibited by
a) Cyanide
b) Carbon dioxide
c) Chocolate
d) Carbonated beverages

Answer: Cyanide
Explanation:
See above explanation.

Q-16. The electron flow in Cytochrome C oxidase can be blocked by: (AIIMS May 2006)
a) Rotenone
b) Antimycin-A
c) Cyanide
d) Actinomycin

Answer: Cyanide
Explanation:
See above explanation.

  1. Cytochrome oxidase in oxidative phosphorylation is inhibited by?
    a) CO
    b) H2S
    c) Cyanide
    d) Amobarbital
    e) Rotenone

Answer: a, b and c
Explanation:
See above explanation.

Q-18. Inhibitor of electron transport, which inhibits transport of ADP in and ATP out of mitochondria – (AIIMS Nov 2010)
a) Atractyloside
b) Oligomycin
c) Rotenone
d) Antimycin-A

Answer: Atractyloside
Explanation:
Inhibitors of oxidative phosphorylation:
Atractyloside inhibits oxidative phosphorylation by inhibiting the transporter of ADP into and ATP out of the mitochondria.
Oligomycin completely blocks oxidation and phosphorylation by blocking the flow of proton through ATP synthase.

Q-19. Dinitrophenol causes:
a) Inhibition of ATP synthase
b) Inhibition of electron transport
c) Uncoupling of oxidation and phosphorylation
d) Accumulation of ATP

Answer: Uncoupling of oxidation and phosphorylation
Explanation:
Un-couplers of oxidative phosphorylation: 2, 4 di-nitro-phenol
Un-couplers dissociate oxidation in the respiratory chain from phosphorylation. Respiration becomes un-controlled and rate is no longer limited by the concentration of ADP or Pi.
Important point:
Un-couplers increase membrane permeability of inner membrane of mitochondria and thus reducing the electrochemical potential. It short circuits the ATP synthase. In this way, oxidation can proceed without phosphorylation.

Q-20. The specialized mammalian tissue/ organ in which fuel oxidation serves not to produce ATP but of generate heat is
a) Adrenal gland
b) Skeletal muscle
c) Brown adipose tissue
d) Heart

Answer: Brown adipose tissue
Explanation:
Thermogenin or un-coupling protein is a physiological un-coupler found in brown adipose tissue that functions to generate body heat, particularly for the new born and during hibernation in animals.

Q-21. Cytosolic Cytochrome C mediates (AIIMS Nov 2006)
a) Apoptosis
b) Electron transport
c) Kreb’s cycle
d) Glycolysis

Answer: Apoptosis
Explanation:
Cytochrome-C is primarily known for its function in the mitochondria as a key participant in the life-supporting function of ATP synthesis.
However, when a cell receives an apoptotic stimulus, cytochrome c is released into the cytosol and triggers programmed cell death through apoptosis.