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2.1 Biochemistry of Metabolism > Sean - The Electron Transport Chain and ATP Synthesis > Flashcards

Sean - The Electron Transport Chain and ATP Synthesis Flashcards

1
Q

What does the TCA cycle produce?

A

3 NADH + H+

1 FADH2

1 GTP

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2
Q

How much ATP does the TCA cycle produce?

A

10 molecules of ATP

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3
Q

How much ATP does NADH + H+ give?

A

NADH+ H+ gives 2.5 ATP each (7.5 ATP in total per cycle)

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4
Q

How much ATP does 1FADH2 give?

A

1.5 ATP per molecule

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5
Q

Where does oxidative phosphorylation occur?

A

The mitochondria

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6
Q

How does oxidative phosphorylation begin?

A

Electrons from NADH and FADH enter the electron transport chain

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6
Q

How does oxidative phosphorylation begin?

A

Electrons from NADH and FADH enter the electron transport chain

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7
Q

What does NAD stand for?

A

Nicotinamide adenine dinucleotide

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8
Q

What does FAD stand for?

A

Flavin adenine dinucleotide

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9
Q

What is the electron transport chain also called?

A

Respiratory chain

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10
Q

What happens when electrons from NAD and FAD enter the electron transport chain?
(2)

A

The electrons are transferred to oxygen

FADH2 and NADH are regenerated to NAD+ and FAD

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11
Q

What is done with the energy from the regeneration of FADH2 and NADH?

A

The energy is used to pump H+ ions across the inner mitochondrial membrane

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12
Q

What results from the pumping of H+ ions across the inner mitochondrial membrane?
(2)

A

It produces a proton gradient across the membrane

This is harnessed by ATP synthase to drive ATP production

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13
Q

What does the electron transport chain consist of?

A

Consists of a series of electron carriers which sit in the inner mitochondrial membrane

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14
Q

Describe what exactly are electron carriers

A

Most of these are integral proteins with prosthetic groups capable of accepting and donating either one or two electrons

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15
Q

List the five electron carriers

A
  1. NAD+
  2. Flavoproteins e.g. FAD, FMN
  3. Ubiquinone (Coenzyme Q)
  4. Iron containing proteins e.g. cytochromes and iron-sulphur proteins
  5. Oxygen
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16
Q

Give two examples of flavoproteins

A

FAD

FMN

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17
Q

What is ubiquinone also called?

A

Coenzyme Q

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18
Q

What is ubiquinone also called?

A

Coenzyme Q

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19
Q

Give two examples of iron containing proteins that act as the fourth electron carrier

A

Cytochromes

Iron-sulphur proteins

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20
Q

Where in the chain can electrons enter the ETC?

A

Can enter at two points:

  1. Electrons from NADH enter the ETC at Complex 1
  2. Electrons from FADH2 enter the ETC at Complex 2
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21
Q

Where do electrons from NADH enter the ETC?

A

Enter at complex 1

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22
Q

Where do electrons from FADH2 enter the ETC?

A

Enter at complex II

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23
Q

In general, what happens in the electron transport chain?

A

Electrons are transferred through the series of membrane bound proteins and chemical electron carriers to oxygen

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24
Q

Explain how H+ ions drive ATP production

A

As the H+ ions go from a high concentration to a low concentration they power the ATP synthase which generates ATP

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25
Q

Name two universal electron acceptors

A

NAD+
FAD

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26
Q

What produces NADH?

A

Its produced from dehydrogenase catalysed reactions

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27
Q

Write a note on NADH

A

Its produced in the matric of the mitochondria through the TCA cycle

It cannot cross the inner mitochondrial membrane

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28
Q

What are two other names for Complex I?

A

NADH dehydrogenase

NADH: ubiquinone oxidoreductase

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29
Q

Write a note on the structure of complex I
(4)

A

Its a large multi-protein complex

It contains 42 different polypeptide chains

Includes an FMN containing flavoprotein

Includes at least 6 iron-sulphur centres

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30
Q

How many polypeptide chains does complex I have?

A

42

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31
Q

What does FMN stand for?

A

Flavon mononucleotide

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32
Q

How many iron-sulphur centres does complex I have?

A

At least 6

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33
Q

What coupled reaction does complex I catalyse?

A
  1. The exergonic transfer of electrons from NADH to ubiquinone
  2. The endergonic pumping of $ H+ from the mitochondrial matric to the intermembrane space
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34
Q

What does complex I produce?

A

Ubiquinol

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35
Q

What is ubiquinol?

A

The fully reduced form of ubiquinone

QH2

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36
Q

What happens to ubiquinol?

A

It diffuses from complex I to complex III in the inner mitochondrial membrane

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37
Q

What happens to ubiquinol at complex III?
(2)

A

It is oxidised to ubiquinone (Q)

Complex III then pumps out protons to the intermembrane space

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38
Q

Give examples of membrane bound electron carriers
(2)

A

Ubiquinone/Coenzyme Q

Cytochromes

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39
Q

What two things can happen to ubiquinone/coenzyme Q?

A

Ubiquinone accepts 1e- to become QH (semiquinone radical)

OR

Ubiquinone accepts 2e- to become QH2

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40
Q

What is QH?

A

Semiquinone radical

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41
Q

Write a note on the properties of ubiquinone
(3)

A

Small + hydrophobic =>

  • can freely diffuse within the lipid bilayer of the inner mitochondrial membrane
  • can shuttle electrons between other less mobile electron carriers in the ETC
42
Q

What are cytochromes?

A

Cytochromes possess an iron containing haem group

43
Q

How many classes of cytochromes do mitochondria contain?

A

3:
- a
- b
- c

44
Q

Comment on the haem groups of each cytochrome class, a, b, c

A

The haem groups of a and b are not covalently attached to the protein

The haem group of c is covalently attached to the protein

45
Q

What is cytochrome a and b?

A

Integral membrane proteins of the inner mitochondrial membrane

46
Q

What is cytochrome c?

A

A soluble protein, that associates with the outer surface of the inner mitochondrial membrane through electrostatic interactions

47
Q

What is complex III also called?

A

Cytochrome bc1 complex

Ubiquinone:cytochrome c oxidoreductase

48
Q

What does complex III do?

A

It couples the transfer of electrons from ubiquinol (QH2) to cytochrome c

49
Q

How does complex III transfer electrons from ubiquinol to cytochrome c?

A

Four protons are pumped against the concentration gradient from the mitochondrial matrix to the intermembrane space

QH2 is oxidised and two molecules of cytochrome c are reduced

50
Q

What is complex IV also called?

A

Cytochrome oxidase

51
Q

What happens in the final step of the ETC?

A

The ETC carries electrons from cytochrome c to O2 which is then reduced to H2O

52
Q

What is cytochrome c?

A

A soluble protein of the intermembrane space

53
Q

How does complex IV bring about the reduction of O2

A

Cytochrome c accepts an electron from complex III and moves it to complex IV

54
Q

How many water molecules are produced for every four electrons that pass through complex IV?

A

2H2O

55
Q

Where does the final step of the ETC get its energy from?

A

Protons are pumped from the matrix to the intermembrane space

56
Q

What are the net effects of complex IV?

A

4e- carried to O2 -> reduced to H2O

2 H+ pumped

57
Q

What is complex II also called?

A

Succinate dehydrogenase

58
Q

Write a note on complex II/succinate dehydrogenase
(4)

A

Succinate dehydrogenase is the only membrane bound enzyme in the citric acid cycle

It plays a role in the electron transport chain

Contains 5 prosthetic groups

Contains 4 protein subunits

59
Q

What 5 prosthetic groups are found in complex II?

A

FAD

3 iron-sulphur centres

Haem B

60
Q

What 4 protein subunits are found in complex II?

A

Two integral membrane subunits

61
Q

How many H+ need to be pumped to process 1 NADH?

A

10 H+

62
Q

How many H+ need to be pumped to process 1 FADH2?

A

6 H+

63
Q

Explain the processing of NADH in the ETC

A

NADH
Complex I
Ubiquinone/Coenzyme Q
Complex III
Cytochrome c
Complex IV
Oxygen
Water

64
Q

Explain the processing of FADH2 in the ETC

A

FADH2
Complex II
Coenzyme Q
Complex III
Cytochrome c
Complex IV
Oxygen
Water

65
Q

Write a note on NADH ETC
(3)

A

2 e- from NADH results in 10x H+ from matrix to intermembrane space

Delivery via complex I

One molecule H2O formed

66
Q

Write a note on FADH2 ETC
(3)

A

2e- from FADH2 results in 6x H+ from matrix to intermembrane space

Delivery via complex II

One molecule H2O formed

67
Q

What is the proton motive force?

A

The energy stored in the gradient created by the pumping of protons across the inner mitochondrial membrane from the mitochondrial matric to the intermembrane space

68
Q

What is the proton motive force made up of?

A

Chemical potential energy:

Electrical potential energy:

69
Q

What is chemical potential energy?

A

The energy associated with the difference in [H+] on either side of the inner mitochondrial membrane

70
Q

What is electrical potential energy?

A

The energy associated with the change in charge

71
Q

What does the proton motive force do?

A

It drives ATP synthesis as protons flow back into the mitochondrial matrix through ATP synthase

‘The chemiosmotic model’

72
Q

What is the chemiosmotic model?

A

The synthesis of ATP as a result of the proton motive force

ATP synthesis as a result of protons flowing back into the mitochondrial matrix through ATP synthase

73
Q

What did Peter Mitchell postulate in relation to the chemiosmotic model?

A

That cells generate ATP by coupling phosphorylation with electrochemical energies associated with differences in proton concentration across the mitochondrial membrane

74
Q

What is complex V also called?

A

ATP synthase

75
Q

What is ATP synthase/complex V?
(3)

A

A large enzyme complex present on the inner mitochondrial membrane

Two components composed of several subunits:
- peripheral membrane protein F1
- integral membrane protein F0

76
Q

What are the two components of ATP synthase/complex V?

A

F1 and F0

77
Q

What is F1?

A

F1 provides the ATP synthase active site i.e. catalyses the phosphorylation of ADP and ATP

78
Q

What is F0?

A

F0 provides a channel through the membrane for the protons to pass

79
Q

What does the proton gradient across the membrane and the F0 channel do?

A

The gradient causes F1 (the enzyme) to release ATP

80
Q

How does the proton gradient cause F1 to release ATP?
(2)

A

Energy is gained by the passive diffusion of H+ ions down their proton gradient

This energy is used to drive a conformational change in ATP synthase (Complex V)

81
Q

List the subunits of F1

A

3 alpha
3 beta
1 gamma
1 delta
1 epsilon

82
Q

How many subunits are there to F1?

A

Nine

83
Q

What’s special about the B subunit of F1?

A

Each B unit has one catalytic site for ATP synthesis and can exist in 3 separate conformations

84
Q

Write about each of the 3 separate conformations of the F1 B subunit

A

B-ATP -> bound to ATP

B-ADP -> bound to ADP

B-empty -> not bound to anything

85
Q

Write about the gamma and epsilon subunits of F1

A

They form a leg and foot which stands on the F0 component

86
Q

What structure does the F0 make up?

A

The proton pore

87
Q

What are the subunits of F0?

A

a, b, c

88
Q

What is subunit c of F0 and what does it do?
(2)

A

A small hydrophobic polypeptide composed of two transmembrane regions

It allows f0 to span the inner mitochondrial membrane

89
Q

What type of catalysis is needed for ATP synthesis?

A

Rotational catalysis

90
Q

Where is rotational catalysis found?

A

This catalyses ATP synthesis and the release from ATP synthase

91
Q

How does catalysis of ATP synthesis work?
(5)

A

The three B subunits of F1 take turns catalysing ATP synthesis

Catalysis starts in the B-ADP conformation

B-ADP binds ADP and Pi -> conformation change to B-ATP

B-ATP binds and stabilises ATP -> conformation change to B-empty

B-empty has low affinity for ATP => ATP leaves surface of F1 enzyme, B-ADP results and process starts afain

92
Q

What does B-ADP bind?

A

ADP and Pi

93
Q

Why is ATP released from B-empty?

A

B-empty has a low affinity for ATP

94
Q

What drives the conformational changes of F1 B subunits in ATP synthesis?

A

Changes are driven by the movement of protons through F0

95
Q

How does the movement of protons through F0 drive the conformational changes of F1 B subunits in ATP synthesis?
(4)

A

The movement of protons cause the cylinder of c subunits (F0) and the gamma subunit of (F1) to rotate perpendicular to the membrane

Contact between the gamma subunit and the B subunits forces one of the B to enter the B-empty conformation

When one B assumes the B-empty the other two assume B-ATP and B-ADP

One complete rotation of the gamma subunit causes each B subunit to cycle through all three conformations

96
Q

How does the gamma subunit of F1 rotate?
(2)

A

The movement of H+ leads to the c subunit rotating

This passes to the gamma and epsilon subunits

97
Q

What happens with the first 120 degree rotation of gamma?

A

This forces the first binding site open

98
Q

What happens with the second 120 degree rotation of gamma?

A

This rotation opens the next binding site and blocks the first site

99
Q

How many protons are needed to make one molecule of ATP?

A

4 protons

100
Q

How many molecules of ATP will NADH make?

A

Between 2 and 3 molecules (2.5 aprox)

101
Q

How many molecules of ATP will FADH2 make?

A

Between 1 and 2 molecules (1.5)

102
Q

Where are the 4 protons required to generate one ATP used?

A

3 protons are required to drive one turn of the ATP synthase complex

1 proton is required to transport free phosphate (PO4) from the cytosol to the mitochondrion

2.1 Biochemistry of Metabolism (21 decks)

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