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Molecules in Medical Science > Oxidative phosphorylation > Flashcards

Oxidative phosphorylation Flashcards

1
Q

What is the overall process of ATP synthesis by oxidative phosphorylation?

A
  1. Oxidation of NADH and FADH2 by O2 releases lots og energy.
  2. This energy is carried by pairs of high energy electrons, which are passed down a chain of electron transporters.
  3. Small amounts of energy is released at each electron transporter.
  4. The electron transporters use this energy to pump H+ ions from the matrix to the intermembrane space.
  5. This creates H+ electrochemical gradient across the inner membrane called the proton motive force.
  6. H+ ions diffuse back into the matrix through channels associated with ATP synthase.
  7. Energy of the diffusing H+ ions used to phosphorylate ADP to ATP in process known as chemiosmosis.
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2
Q

What are the effects of uncouplers?

A
  • Makes the inner mitochondrial membrane more leaky to H+ ions, reducing the PMF.
  • This makes the mitochondria less efficient at producing ATP from the breakdown of fuels.
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3
Q

What is the name of complex I?

A

NADH-Q reductase

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4
Q

What is the name of complex II?

A

Succinate-Q reductase (inc. succinate dehydrogenase)

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5
Q

What is the name of complex III?

A

Q-cytochrome c oxidoreductase

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6
Q

What is the name of complex IV?

A

Cytochrome c oxidase

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7
Q

What is the general principle of the ETC?

A

The complexes are simply a series of trnasmembrane enzymes catalysing redox reactions between the different mobile electron carriers in the ETC.

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8
Q

What is the function of complex I?

A

Oxidation of NADH to NAD+ with the pair of electrons being transported to CoQ.

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9
Q

What is the mechanism of action of complex I?

A
  • Complex I has 2 arms:
    1. Peripheral arm - Site of electron transport
    2. Transmembrane arm - Site of proton pumping
  • In the peripheral arm, a pair of electrons are removed from NADH and passed down a series of electron carriers, starting with FMN and followed by 8 FeS groups, before being passed to CoQ.
  • Conformational change induced by electron transfer in the peripheral arm causes transmembrane arm to pump 4 H+ ions from the matrix into the intermembrane space.
  • 9th FeS in peripheral arm prevents formation of ROSs.
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10
Q

What is significant about electron transport between electron carriers in the complexes?

A
  • Electron carriers within different complexes are usually
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11
Q

What is the function of complex II?

A
  • Oxidation of succinate to fumarate.

- Re-oxidation of FADH2 to FAD and the transfer of a pair of electrons to CoQ.

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12
Q

What is the mechanism of action of complex II?

A
  • Complex II contains succinate dehydrogenase, a CAC enzyme.
  • Succinate is oxidised to fumarate within the complex, with FAD being reduced to FADH2.
  • FADH2 is actually part of the complex itself and so is immediately reoxidised.
  • Pair of electrons is released and passed down a sequence of 3 FeS complexes before being passed to CoQ.
  • Haem group may be present to prevent the formation of ROSs.
  • The amount of energy released from the oxidation of FADH2 is insufficient to drive the active transport of H+ ions across the membrane.
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13
Q

What is the function or complex III?

A

Transfers electrons from CoQ (reduced) to cytochrome c.

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14
Q

What is the mechanism of action of complex III?

A
  • Electrons are passed to an FeS complex. Then, they are transferred to cytochrome bc1, which is closely associated with cytochrome c.
  • Electrons are transferred from cytochrome c1 to cytochrome c.
  • Energy released from this process is used to pump 4 H+ ions from the matrix into the intermembrane space.
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15
Q

What is the function of the Q-cycle?

A

The Q-cycle allows the net oxidation of 1 CoQ to pump 4 H+ ions from the matrix into the intermembrane space.

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16
Q

What is the function of complex IV?

A

Transfers electrons from cytochrome c to O2, which is converted to H2O. O2 + 4e- + 4H+ → 2H2O.

17
Q

What is the mechanism of action of complex IV?

A
  • Complex IV contains 4 redox centres:
    1. CuA (with 2 Cu atoms)
    2. Cytochrome a
    3. Cytochrome a3
    4. CuB
  • These 4 redox centres work together to ensure that O2 is fully oxidised to H2O.
  • For every pair of electrons, the complex pumps 2H+ ions from the matrix into the intermembrane space. However, 2 further H+ ions are lost from the matrix in H2O production, which steepens the proton gradient.
18
Q

What are the different electron carriers in the ETC?

A
  • FAD: Capable of carrying 2 electrons as FADH2.
  • FMN
  • FeS complexes: Capable of carrying 1 electron each.
  • CoQ: Capable of carrying 2 electrons from complex I/II to III.
  • Cytochromes: Capable of carrying 1 electron each due to containing Fe2+/Fe3+.
    Cu: Acts as redox centres in complex IV.
19
Q

What are the different types of cytochromes?

A
  • Cytochrome a, a3: Found in complex IV.
  • Cytochrome b, c1: Found in complex III.
  • Cytochrome c: Transfers electrons between complex III and IV.
20
Q

How can the absorption spectrum of cytochrome c be distinguished?

A

Reduced cytochrome c has 2 characteristic α and β peaks between 500-600 nm.

21
Q

What is proton motive force?

A

Force that drives the diffusion of H+ ions from the intermembrane space back into the matrix as a result of the electrochemical gradient.

22
Q

What is the basis of chemiosmosis?

A

Energy from the diffusion of H+ ions down the electrochemical gradient, from the intermembrane space to the matrix, is used in the process of ATP synthesis. This coupling is achieved by ATP synthase.

23
Q

What is the equation for the phosphorylation of ATP?

A

ADP + Pi → ATP + H2O

24
Q

What is the gross structure of ATP synthase?

A

ATP synthase consists of 2 subunits:

  1. F0: Transmembrane domain, through which H+ ions diffuse. It is known as the ‘rotory engine’ part of ATP synthase.
  2. F1: Peripheral domain, site of ATP synthesis.
25
Q

What is the specific structure of F0 domain?

A
  • a subunit
  • 2 b subunits forming stalk linking a subunit in F0 to δ subunit in F1.
  • 10 c subunits in ring shape.
  • Each subunit has H+ binding site.
  • Binding and release of H+ from F0 causes its rotation, which causes conformational changes in F1 that drive ATP synthesis.
26
Q

What is the specific structure of F1 domain?

A
  • F1 consists of 9 subunits.
  • 3 pairs of αβ subunits arranged around and attached to central γ subunit in a ring shape. Each pair forms ATP binding site.
  • γ, δ, ε subunits all connect F1 to F0.
  • γ subunit directly involved in transferring conformational change from F0 to F1.
27
Q

How is energy generated by F0 for ATP synthesis in F1?

A
  1. H+ binds to a c subunit, causing a conformational change that causes c ring to rotate by 1 subunit.
  2. Another c subunit releases its H+ ion into the matrix, freeing up a H+ binding site for another H+ from the intermembrane space to bind to F0.
  3. Process repeats and the F0 subunit continuously rotates, driving conformational changes in the γ subunit of F1, which is transferred to the αβ binding sites.
  4. This drives the process of ATP synthesis in F1.
28
Q

What are the states of the ATP binding sites on the F1 subunit?

A
  • Open (O): Nothing bound.
  • Loose (L): Bound to ADP and Pi.
  • Tight (T): Catalyses reaction between ADP and Pi to form ATP.
29
Q

What is the process of ATP synthesis in F1 subunit?

A
  1. ADP and Pi to binding site in L state.
  2. Energy from rotating F0 used to drive conformational change of binding site from L state to T state.
  3. ATP is formed as the T state catalyses the ADP + Pi → ATP + H2O.
  4. Energy is used to convert T state to O state, which causes ATP to be released.
30
Q

What is the majority of energy from PMF used for during ATP synthesis?

A

Conversion of the T state binding site to O state, i.e. releasing the bound ATP.

31
Q

What is the stoichiometry of ATP synthase?

A
  • ~3 H+ ions need to cross the ATP synthase in order to produce 1 ATP molecule.
  • ~3 ATP molecules are synthesised per turn of F0.
  • Assuming 100% efficiency, ~3 ATP molecules can be synthesised per NADH molecule reoxidised and ~2 from FADH2 reoxidation.
  • Taking into account proton leakage (for phosphate transport into or ATP transport out of cells), ~2.5 ATP molecules are synthesised per NADH and ~1.5 ATP molecules are synthesised per FADH2.
32
Q

Which compound opposes the formation of free radicals?

A

Reduced glutathione (GSH)

33
Q

What is an inhibitor of complex I?

A

Rotenone

34
Q

What is an inhibitor of complex III?

A

Antimycin

35
Q

What is an inhibitor of complex IV?

A

Cyanide

36
Q

What is an inhibitor of ATP synthase?

A

Oligomycin

37
Q

How is ADP transported into the mitochondria?

A
  • Adenosine nucleotide translocase

- ADP is exchanged for ATP

38
Q

How is phosphate transported into the mitochondria?

A
  • Phosphate translocase

- By symport with H+

Molecules in Medical Science (15 decks)

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