Sean - The Electron Transport Chain and ATP Synthesis Flashcards
What does the TCA cycle produce?
3 NADH + H+
1 FADH2
1 GTP
How much ATP does the TCA cycle produce?
10 molecules of ATP
How much ATP does NADH + H+ give?
NADH+ H+ gives 2.5 ATP each (7.5 ATP in total per cycle)
How much ATP does 1FADH2 give?
1.5 ATP per molecule
Where does oxidative phosphorylation occur?
The mitochondria
How does oxidative phosphorylation begin?
Electrons from NADH and FADH enter the electron transport chain
How does oxidative phosphorylation begin?
Electrons from NADH and FADH enter the electron transport chain
What does NAD stand for?
Nicotinamide adenine dinucleotide
What does FAD stand for?
Flavin adenine dinucleotide
What is the electron transport chain also called?
Respiratory chain
What happens when electrons from NAD and FAD enter the electron transport chain?
(2)
The electrons are transferred to oxygen
FADH2 and NADH are regenerated to NAD+ and FAD
What is done with the energy from the regeneration of FADH2 and NADH?
The energy is used to pump H+ ions across the inner mitochondrial membrane
What results from the pumping of H+ ions across the inner mitochondrial membrane?
(2)
It produces a proton gradient across the membrane
This is harnessed by ATP synthase to drive ATP production
What does the electron transport chain consist of?
Consists of a series of electron carriers which sit in the inner mitochondrial membrane
Describe what exactly are electron carriers
Most of these are integral proteins with prosthetic groups capable of accepting and donating either one or two electrons
List the five electron carriers
- NAD+
- Flavoproteins e.g. FAD, FMN
- Ubiquinone (Coenzyme Q)
- Iron containing proteins e.g. cytochromes and iron-sulphur proteins
- Oxygen
Give two examples of flavoproteins
FAD
FMN
What is ubiquinone also called?
Coenzyme Q
What is ubiquinone also called?
Coenzyme Q
Give two examples of iron containing proteins that act as the fourth electron carrier
Cytochromes
Iron-sulphur proteins
Where in the chain can electrons enter the ETC?
Can enter at two points:
- Electrons from NADH enter the ETC at Complex 1
- Electrons from FADH2 enter the ETC at Complex 2
Where do electrons from NADH enter the ETC?
Enter at complex 1
Where do electrons from FADH2 enter the ETC?
Enter at complex II
In general, what happens in the electron transport chain?
Electrons are transferred through the series of membrane bound proteins and chemical electron carriers to oxygen
Explain how H+ ions drive ATP production
As the H+ ions go from a high concentration to a low concentration they power the ATP synthase which generates ATP
Name two universal electron acceptors
NAD+
FAD
What produces NADH?
Its produced from dehydrogenase catalysed reactions
Write a note on NADH
Its produced in the matric of the mitochondria through the TCA cycle
It cannot cross the inner mitochondrial membrane
What are two other names for Complex I?
NADH dehydrogenase
NADH: ubiquinone oxidoreductase
Write a note on the structure of complex I
(4)
Its a large multi-protein complex
It contains 42 different polypeptide chains
Includes an FMN containing flavoprotein
Includes at least 6 iron-sulphur centres
How many polypeptide chains does complex I have?
42
What does FMN stand for?
Flavon mononucleotide
How many iron-sulphur centres does complex I have?
At least 6
What coupled reaction does complex I catalyse?
- The exergonic transfer of electrons from NADH to ubiquinone
- The endergonic pumping of $ H+ from the mitochondrial matric to the intermembrane space
What does complex I produce?
Ubiquinol
What is ubiquinol?
The fully reduced form of ubiquinone
QH2
What happens to ubiquinol?
It diffuses from complex I to complex III in the inner mitochondrial membrane
What happens to ubiquinol at complex III?
(2)
It is oxidised to ubiquinone (Q)
Complex III then pumps out protons to the intermembrane space
Give examples of membrane bound electron carriers
(2)
Ubiquinone/Coenzyme Q
Cytochromes
What two things can happen to ubiquinone/coenzyme Q?
Ubiquinone accepts 1e- to become QH (semiquinone radical)
OR
Ubiquinone accepts 2e- to become QH2
What is QH?
Semiquinone radical
Write a note on the properties of ubiquinone
(3)
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
What are cytochromes?
Cytochromes possess an iron containing haem group
How many classes of cytochromes do mitochondria contain?
3:
- a
- b
- c
Comment on the haem groups of each cytochrome class, a, b, c
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
What is cytochrome a and b?
Integral membrane proteins of the inner mitochondrial membrane
What is cytochrome c?
A soluble protein, that associates with the outer surface of the inner mitochondrial membrane through electrostatic interactions
What is complex III also called?
Cytochrome bc1 complex
Ubiquinone:cytochrome c oxidoreductase
What does complex III do?
It couples the transfer of electrons from ubiquinol (QH2) to cytochrome c
How does complex III transfer electrons from ubiquinol to cytochrome c?
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
What is complex IV also called?
Cytochrome oxidase
What happens in the final step of the ETC?
The ETC carries electrons from cytochrome c to O2 which is then reduced to H2O
What is cytochrome c?
A soluble protein of the intermembrane space
How does complex IV bring about the reduction of O2
Cytochrome c accepts an electron from complex III and moves it to complex IV
How many water molecules are produced for every four electrons that pass through complex IV?
2H2O
Where does the final step of the ETC get its energy from?
Protons are pumped from the matrix to the intermembrane space
What are the net effects of complex IV?
4e- carried to O2 -> reduced to H2O
2 H+ pumped
What is complex II also called?
Succinate dehydrogenase
Write a note on complex II/succinate dehydrogenase
(4)
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
What 5 prosthetic groups are found in complex II?
FAD
3 iron-sulphur centres
Haem B
What 4 protein subunits are found in complex II?
Two integral membrane subunits
How many H+ need to be pumped to process 1 NADH?
10 H+
How many H+ need to be pumped to process 1 FADH2?
6 H+
Explain the processing of NADH in the ETC
NADH
Complex I
Ubiquinone/Coenzyme Q
Complex III
Cytochrome c
Complex IV
Oxygen
Water
Explain the processing of FADH2 in the ETC
FADH2
Complex II
Coenzyme Q
Complex III
Cytochrome c
Complex IV
Oxygen
Water
Write a note on NADH ETC
(3)
2 e- from NADH results in 10x H+ from matrix to intermembrane space
Delivery via complex I
One molecule H2O formed
Write a note on FADH2 ETC
(3)
2e- from FADH2 results in 6x H+ from matrix to intermembrane space
Delivery via complex II
One molecule H2O formed
What is the proton motive force?
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
What is the proton motive force made up of?
Chemical potential energy:
Electrical potential energy:
What is chemical potential energy?
The energy associated with the difference in [H+] on either side of the inner mitochondrial membrane
What is electrical potential energy?
The energy associated with the change in charge
What does the proton motive force do?
It drives ATP synthesis as protons flow back into the mitochondrial matrix through ATP synthase
‘The chemiosmotic model’
What is the chemiosmotic model?
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
What did Peter Mitchell postulate in relation to the chemiosmotic model?
That cells generate ATP by coupling phosphorylation with electrochemical energies associated with differences in proton concentration across the mitochondrial membrane
What is complex V also called?
ATP synthase
What is ATP synthase/complex V?
(3)
A large enzyme complex present on the inner mitochondrial membrane
Two components composed of several subunits:
- peripheral membrane protein F1
- integral membrane protein F0
What are the two components of ATP synthase/complex V?
F1 and F0
What is F1?
F1 provides the ATP synthase active site i.e. catalyses the phosphorylation of ADP and ATP
What is F0?
F0 provides a channel through the membrane for the protons to pass
What does the proton gradient across the membrane and the F0 channel do?
The gradient causes F1 (the enzyme) to release ATP
How does the proton gradient cause F1 to release ATP?
(2)
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)
List the subunits of F1
3 alpha
3 beta
1 gamma
1 delta
1 epsilon
How many subunits are there to F1?
Nine
What’s special about the B subunit of F1?
Each B unit has one catalytic site for ATP synthesis and can exist in 3 separate conformations
Write about each of the 3 separate conformations of the F1 B subunit
B-ATP -> bound to ATP
B-ADP -> bound to ADP
B-empty -> not bound to anything
Write about the gamma and epsilon subunits of F1
They form a leg and foot which stands on the F0 component
What structure does the F0 make up?
The proton pore
What are the subunits of F0?
a, b, c
What is subunit c of F0 and what does it do?
(2)
A small hydrophobic polypeptide composed of two transmembrane regions
It allows f0 to span the inner mitochondrial membrane
What type of catalysis is needed for ATP synthesis?
Rotational catalysis
Where is rotational catalysis found?
This catalyses ATP synthesis and the release from ATP synthase
How does catalysis of ATP synthesis work?
(5)
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
What does B-ADP bind?
ADP and Pi
Why is ATP released from B-empty?
B-empty has a low affinity for ATP
What drives the conformational changes of F1 B subunits in ATP synthesis?
Changes are driven by the movement of protons through F0
How does the movement of protons through F0 drive the conformational changes of F1 B subunits in ATP synthesis?
(4)
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
How does the gamma subunit of F1 rotate?
(2)
The movement of H+ leads to the c subunit rotating
This passes to the gamma and epsilon subunits
What happens with the first 120 degree rotation of gamma?
This forces the first binding site open
What happens with the second 120 degree rotation of gamma?
This rotation opens the next binding site and blocks the first site
How many protons are needed to make one molecule of ATP?
4 protons
How many molecules of ATP will NADH make?
Between 2 and 3 molecules (2.5 aprox)
How many molecules of ATP will FADH2 make?
Between 1 and 2 molecules (1.5)
Where are the 4 protons required to generate one ATP used?
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
