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BMB 402 > Chapter 11 Oxidative Phosphorylation > Flashcards

Chapter 11 Oxidative Phosphorylation Flashcards

1
Q

Chemiosmotic theory

A

Peter Mitchell’s theory that energy captured by coupled redox reactions in an electron transport system translocates protons across a membrane, which creates an electrochemical gradient that is used to drive ATP synthesis via proton flow through ATP synthase

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2
Q

Where is the proton gradient established?

A

across the inner mitochondrial membrane

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3
Q

Chemiosmosis

A

The generation of ATP as a result of the flow of protons across a membrane in response to a concentration gradient

  • flows from high [H+] to low [H+]
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4
Q

Describe the flow of protons during chemiosmosis

A

Proton gradient is initiated by outward pumping of H+ from the mitochondrial matrix by three protein complexes

The inward flow of H+ through membrane bound ATP synthase accomplishes ATP synthesis

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5
Q

What is the overall net reaction of the oxidative phosphorylation pathway?

A

2 NADH + 2 H+ + 5 ADP + 5 Pi + O2 → 2 NAD+ + 5 ATP + 2 H2O

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6
Q

How is oxidative phosphorylation regulated?

A

The main regulator of this process is the ADP/ATP ratio. It is upregulated by high ADP (low energy) and Pi. Inhibition of any of the previous processes (Glycolysis, Citrate Cycle) will downregulate it.

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7
Q

What is the electron transport system?

A

A series of proteins embedded in the inner mitochondrial membrane that converts the energy of redox reactions to a proton potential

Reactions in the ETC result in the coupled oxidation of NADH and FADH2 with the reduction of O2 to form NAD+ and H2O, providing free energy for ATP synthesis

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8
Q

Why is the order of complexes in the ETC vital to its function?

A

The electron carriers that participate in the ETC are ordered from most negative standard reduction potential to most positive, which allows a sequential transfer of protons and electrons at each step. The electron affinity of each carrier increases up to O2, which is the final electron acceptor.

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9
Q

What is the final electron acceptor of the electron transport system?

A

O2

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10
Q

What is the proton circuit?

A

the cyclical movement of protons across a membrane as a function of the electron transport system, which then flow back down their concentration gradient across the same membrane through a protein channel

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11
Q

What happens if the proton circuit is uncoupled?

A

If it is uncoupled, ATP synthesis no longer occurs

Uncoupling can also cause proton leakage across the membrane (without making ATP), causing heat production

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12
Q

What is oligomycin?

A

an antibiotic that blocks the synthesis of ATP by inhibiting the activity of the F0 proton channel of the ATP synthase complex

It inhibits the ETC and causes cell death

accumulation of protons causes a large change in pH

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13
Q

What are some structural features of the mitochondria?

A
  • outer mitochondrial membrane
  • intermembrane space (where protons are pumped to)
  • inner mitochondrial membrane
  • cristae
  • mitochondrial matrix
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14
Q

What are cristae?

A

folded areas of the inner mitochondrial membrane that greatly increases surface area for chemiosmotic production of ATP

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15
Q

What are the five protein components of the electron transport system?

A
  1. NADH-ubiquinone oxidoreductase
  2. Succinate dehydrogenase
  3. Ubiquinone-cytochrome c oxidoreductase
  4. Cytochrome c oxidase
  5. ATP synthase
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16
Q

Complex I

A

NADH-ubiquinone oxidoreductase

catalyzes the first redox reaction where NADH oxidation is coupled to flavin mononucleotide (FMN) reduction and translocates 4H+ into the intermembrane space

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17
Q

Complex II

A

Succinate dehydrogenase

catalyzes an oxidation reaction converting succinate to fumerate (does not transport H+ across membrane)

Reduces coenzyme Q to QH2

ALSO FOUND IN THE CITRATE CYCLE

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18
Q

Complex III

A

Ubiquinone-cytochrome c oxidoreductase

translocates 4H+ across the membrane via the Q cycle and facilitates electron transfer to cytochrome C (which brings electrons to complex IV)

19
Q

Complex IV

A

Cytochrome c oxidase

translocates 2H+ into the intermembrane space and catalyzes the reduction of molecular oxygen to form water

accepts electrons one at a time from cytochrome c (which is oxidized while oxygen in reduced)

20
Q

Complex V

A

ATP synthase

21
Q

How do Complexes I-IV differ from Complex V?

A

Complexes I-IV contain transmembrane regions that are embedded in the inner mitochondrial membrane and they catalyze the movement of protons.

Complex V is ATP synthase; generates ATP due to proton flow

22
Q

Where is NADH oxidized?

A

Complex I

23
Q

Where is FADH2 oxidized?

A

Complex II

24
Q

What is coenzyme Q?

A

a mobile electron carrier that moves laterally within the inner membrane between protein complexes of the ETC; is the entry point of two electrons from the citrate cycle, fatty acid oxidation, and G3P dehydrogenase

aka ubiquinone

reduced coenzyme Q brings electrons from Complex I to III

25
Q

What is cytochrome C?

A

a mobile electron carrier protein that moves in the intermembrane space between complexes III and IV

26
Q

Which complexes actually function as “pumps?”

A

Complexes I and IV

27
Q

How do redox loops function and what is an example?

A

they separate protons and electrons on opposite sides of the membrane

an example is the Q cycle (done by Complex III)

28
Q

What are examples of ETC inhibitors?

A
  • Rotenone
  • Hydrogen cyanide
  • carbon monoxide
  • antimycin A
29
Q

How does cyanide work?

A

It binds to the heme group in complex IV, blocking electron transport and preventing reduction of oxygen to water, leading to death

30
Q

Overall, what does oxidative phosphorylation accomplish for the cell?

A

It generates ATP derived from the oxidation of metabolic fuels, accounting for 28 of 32 (88%) obtained from glucose catabolism in most cells

31
Q

What are the key enzymes of oxidative phosphorylation?

A

the five complexes

32
Q

What is the Q Cycle?

A

A redox loop that converts a 2 electron transport process into two 1 electron transfers.

This process occurs in Complex III. Electrons come from coenzyme Q, and cytochrome C is reduced in the process. Cytochrome C transports 1 electron at a time from Complex III to IV

33
Q

What are the two structural components of ATP synthase?

A

F1 and F0 (“F nought”)

34
Q

What does F1 do?

A

encodes the catalytic activity of ATP synthase

35
Q

What does F0 do?

A

Acts as a proton channel crossing the inner mitochondrial membrane

36
Q

What are the parts of the ATP synthase complex?

A

Rotor: has gamma, delta, and epsilon subunits
Headpiece: catalytic piece and alpha and beta subunits
Stator: stabilizing arm (immobile)

37
Q

Describe the process of proton flow through ATP synthase along with ATP generation

A
  • protons flow through F0
  • F1 subunit undergoes conformational change from L (loose), T (tight), and O (open)
  • rotor rotates 120 degrees
  • ADP and P bind to form ATP
  • ATP is released only in the open position
38
Q

What two shuttles move biomolecules across the membrane for oxidative phosphorylation?

A

malate-aspartate shuttle (liver)
Glycerol-3-phosphate shuttle (muscle)

39
Q

How does the malate-aspartate shuttle work?

A

NADH reduces MDH to malate, which goes across the membrane and regenerates NADH in the matrix, and recovers OAA

Its main goal is to get NADH from the cytoplasm to the mitochondria and maintain supply of NAD+

40
Q

How does glycerol-3-phosphate work?

A

It can give electrons to coenzyme Q, which goes to Complex III

41
Q

How is ADP imported into the mitochondrial matrix and how is ATP exported?

A

the enzyme ATP/ADP translocase exports one ATP for every ADP imported (antiport transporter)

42
Q

How does P enter the mitochondrial matrix?

A

Phosphate translocase translocates one P and one H+ into the matrix (can be an antiporter or symporter)

43
Q

What controls aerobic respiration?

A

ADP and ATP

44
Q

How is thermogenesis achieved in brown fat?

A

Brown fat contains uncoupling proteins for H+ to go through instead of ATP synthase, resulting in the production of heat

BMB 402 (14 decks)

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