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Cellular and Molecular Biology > L32: Oxidative Phosphorylation > Flashcards

L32: Oxidative Phosphorylation Flashcards

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1
Q
A
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2
Q

Where does oxidative phosphorylation take place?

A

In the mitochondria

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3
Q

What is oxidative phosphorylation?

A

The process in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers

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4
Q

In oxidative phosphorylation, what happens when oxygen accepts electrons from NADH and FADH2?

A

Oxygen is reduced to water

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5
Q

Why is the inner mitcohondrial membrane convulated>?

A

The inner membrane’s folds (cristae) increase the surface area, facilitating the high concentration of embedded proteins necessary for electron transport.

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6
Q

How are NADH and FADH2 brought into the mitochonria?

A

Via shuttles

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7
Q

Is it true that the inner mitochondrial membrane is impermeable to NADH?

A

Yes

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8
Q

Why doesn’t cytosolic NADH (i.e. from glycolysis) get into the matrix?

A

It doesn’t, because the inner mitochondrial membrane is impermeable to NADH. But electrons from NADH enter the mitochondrial matrix

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9
Q

Which 2 shuttles transport electrons from NADH across the mitochondrial membranes?

A

glycerol phosphate shuttle

malate shuttle

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10
Q

Is oxidative phosphorylation aerobic or anaerobic?

A

Aerbic, and it stops without the presence of oxygen

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11
Q

What is the purpose of oxidative phosphorylation?

A

To harvest energy from NADH and FADH2 to produce ATP.

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12
Q

what is the mitochondrial matrix the site of?

A

the citric acid cycle

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13
Q

What does the citric acid cycle produce?

A

Acetyl-CoA oxidation produces 6 NADH, 2 FADH2, and 2 GTP.

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14
Q

Describe the glycerol phosphate shuttle

A
  • Cytoplasmic NADH reduces dihydroxyacetone phosphate (DHAP) to glycerol-3-phosphate (G3P).
  • G3P enters the mitochondria and is oxidized back to DHAP by mitochondrial glycerol-3-phosphate dehydrogenase, transferring electrons to FAD, forming FADH2.
  • FADH2 enters the ETC at ubiquinone (Complex III), bypassing Complex I.
  • Efficiency Loss: Produces ~1.5 ATP per NADH instead of 2.5 ATp, as only 6H+ pumped instead of 10.
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15
Q

Describe the malate shuffle

A
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16
Q

When is the malate shuffle used?

A

In organs like the heart and liver, where energy(ATP) must be conserved

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17
Q

Describe the malate shuttle

A
  • Used in heart and liver
  • A complex redox shuttle. The process involves transferring electrons via malate, oxaloacetate, aspartate, and other intermediates in a cycle.
  • Net reaction is NADH moved to
    mitochondria
  • Produces more ATP than the other shuttle
  • It avoids energy loss associated with bypassing Complex I in the electron transport chain (ETC).
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18
Q

How does ADP and Pi get into the matrix and how does ATP get into the cytosol?

A

Using antiporters

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19
Q

Moevement in ETC when you start with NADH

A

NADH➞ cpx I ➞ cpx III ➞ cpx IV ➞ O2

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20
Q

Moevement in ETC when you start with FADH2

A

FADH2➞ cpx II ➞ cpx III ➞ cpx IV ➞ O2

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21
Q

Are the respiratory complexes just different parts of the electron transport chain?

A

Yes

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22
Q

Do the complexes themselves make ATP?

A

No, they facilitate the necessary energy for the production of ATP by pumping protons into the inter-membrane space. ATP synthase tehn uses this proton gradient to synthesise ATP.

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23
Q

ETC in terms of energetics

A
  • Moving from lower to higher redox potentials.
  • More free energy is released as you move across theETC
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24
Q

Describe complex I

A
  • The first protein complex of the ETC.
  • NADH is oxidised to NAD+ and the electrons from this are transferred to ubiquinone (Q).
  • The redox potential is becoming more positive i.e., ∆E is positive . So ∆G is negative (free energy is released).
  • The overall result is that 4 protons pumped across membrane
25
Q

What prosthetic groups are involved in electron transport in complex I?

A

Flavin

Iron sulfur Clusters (very good at carrying electrons + have quite low redox potentials0

26
Q

Describe complex III

A
  • Includes iron sulfur complexes and cytochromes. (cytochromes have highe redox potential, allow for release of free energy).
  • Ubiquinone to deleivers electorns to Cytochrome C. Cytochrome C can only carry one electron at a time due to its Heme (iron) group
  • Relay of 2 electron (from ubiquinone) to 1 electron carrier called Q cycle
  • 4 protons are pumped across the membrane overall (2 from complex itself, and 2 from the Q cycle)
27
Q

Q cycle

A
  • Ubiquinone becomes fully oxidised
  • Ubiquinone delivers its electrons to complex 3 and 2 protons go across the membrane.
  • One electron gets ferried on to cytochrome C and cytochrome C can then leave.
  • The other electron then goes to a semi-quinone
  • a new ubiqunnone will then come in with more electrons
  • one electron will be carried off by cytochrome C.
  • The other electron will then go down and reduce the semi quinone to a fully reduced form of quinone.
  • That quinone will then leave back out to the membrane and get rid of its electrons
28
Q

Describe Complex IV

A
  • Also consists of cytochromes and cupper
  • Cytochrome C delivers electrons to Oxygen.
  • Oxygen is the final electron acceptor will be reduced to water.
  • Free energy will be released.
  • Result: 2 protons pumped across membrane
  • Oxygen reduction is tightly controlled because the intermediates (e.g., superoxide, peroxide) are highly reactive and damaging if they escape.
29
Q

Describe complex II

A
  • Complex II is a smaller complex in the electron transport chain.
  • Complex II accepts electrons from FADH₂ produced during the citric acid cycle.
  • These electrons are transferred to ubiquinone (Q), reducing it to ubiquinol (QH₂).
  • Complex II contains: FAD, Iron-sulfur (Fe-S) clusters, Heme b
  • Unlike Complex I, Complex II does not pump protons into the intermembrane space.
  • This means that electrons entering the ETC via Complex II contribute less to the proton gradient and result in fewer ATP molecules (~1.5 ATP per FADH₂).
  • It forms a direct link between the citric acid cycle and the electron transport chain.
30
Q

Complexes can exist individually, but how else can complexes also exist?

A

as super-complexes called respirasomes

31
Q

Describe respiratory super-complexes

A
  • Adapter proteins are needed
  • Advantage more efficient transfer
  • But too effective might result in reactive oxygen species
  • We don’t know much about how this is regulated
32
Q

What did Peter Mitchell propose in 1961?

A

That the primary energy-conserving event induced by e- transport is the generation of a proton-motive force across the inner mitochondrial membrane. Basically, that the ETC builds a proton gradient, which indirectly drives ATP synthesis through a proton motive force (PMF).

33
Q

Why were Pere’s ideas intially met with skepticism?

A

because researchers at the time expected a chemical intermediate (similar to glycolysis) to directly link the ETC to ATP production.

34
Q

When did Peter Mitchell receive a nobel prize?

A

in the late 1970s.

35
Q

Describe the mechanism of chemeosmosis

A
  • The ETC pumps protons from the matrix into the intermembrane space, resulting in:
    Low Proton Concentration: In the matrix (higher pH, more negative charge).

High Proton Concentration: In the intermembrane space (lower pH, more positive charge).

-

36
Q

Which factors contribute to the proton-motive force

A
  • A concentration gradient : ΔpH ~ -1.4
  • A transmembrane potential: Em ~ 0.14 V
37
Q

How many hydrogen ions are needed for one ATP?

A

One

38
Q

What are the 2 parts of ATP synthase?

A
  • F0(membrane part) and F1
  • Without F1, F0 pumps protons but does not make ATP
  • Isolated F1 hydrolyses ATP (reverse reaction)
  • Thus, ATP synthesis requires F0 (proton pumping) and F1 (ATPase) to be coupled
  • ATP is formed in the catalytic site of F1 but it is not released unless H+ flow through F0
39
Q

Describe ATP synthase

A

protons flow back into the matrix via the F₀ subunit, causing the shaft to rotate.

The rotational energy drives conformational changes in the F₁ subunit, leading to ATP synthesis from ADP and Pi.

40
Q

Is it true that the ‘Rotation of 𝛾 causes changes in the conformation of the 𝛽 catalytic sites
‘?

A

Yes

41
Q

F₀ Unit:

A

Embedded in the mitochondrial membrane; allows proton flow.

42
Q

F₁ Unit

A

Faces the matrix; contains catalytic sites for ATP synthesis.

43
Q

The γ (gamma) subunit

A

The γ (gamma) subunit is a central shaft connecting the F₀ and F₁ units.

44
Q

Rotation of 𝛾

A

Protons flow down their gradient from the intermembrane space into the matrix through the F₀ unit.

This flow provides the energy needed to rotate the γ shaft.

As the γ shaft rotates, it interacts with the β subunits of the F₁ unit.

This rotation induces conformational changes in the β subunits, which are essential for ATP synthesis.

The β subunits cycle through three states:
O (Open): Allows ADP and Pi to bind or ATP to be released.

L (Loose): ADP and Pi are held loosely, preventing them from escaping.

T (Tight): ADP and Pi are forced together to form ATP. ATP is held tightly in this state.

The rotation of the γ shaft changes which β subunit is in each state, allowing continuous synthesis and release of ATP.

The rotation of the γ shaft changes which β subunit is in each state, allowing continuous synthesis and release of ATP.

45
Q

What controls oxidative phosphorylation?

A

The need for ATP. Electrons do not flow from NADH to O2 unless ATP is being synthesised .

46
Q

What determines the rate of respiration?

A

the level of ADP determines the rate

47
Q

Uncoupling of the electron transport chain and ATP synthesis, resulting in no ATP synthesis, has been a pharmacological target for decades to combat obesity, but isn’t currently used because……

A

Temperature of the individual can increase dangerously

48
Q

What can natural uncoupling generate?

A

Heat

49
Q

Describe what thermogenin, the uncoupling protein in animals, does?

A

Found in mitochondria of brown fat cells

natural uncoupler

maintains body temperature e.g., in babies and during wake up from hibernation

50
Q

Describe what Alternative oxidase , the uncoupling protein in plants, does?

A

Oxidises QH2 and generates heat

used by some species to increase temperature of specific organs i.e., flowers or to germinate early

51
Q

In oxidative phosphorylation, how many ATP are made for each NADH?

A

2.5 ATP made for each NADH

52
Q

In oxidative phosphorylation, how many ATP are made for each FADH2?

A

1.5 ATP made for each FADH2

53
Q

In respiration, how many ATP are generated per glucose molecule in oxidative conditions?

A

30

54
Q

What is the efficiency of respiration?

A

52%

55
Q

What goes into the electron transport chain in the mitochondria?

A

Reduced co enzymes NADH and FADH₂

56
Q

How many complexes are there?

A

4

57
Q

How many proton pumps are there?

A

3

58
Q
A

Cellular and Molecular Biology (33 decks)

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