Oxidative phosphorylation Flashcards
What is oxidative phosphorylation basically?
Transferring NADH from the cytoplasm to the mitochondrial membrane
Is Transferring NADH from the cytoplasm to the mitochondrial membrane direct and why?
No as no NADH transporters on the inner mitochondrial membrane
Where is the [NADH] greater. Matrix or cytoplasm?
Matrix> cytoplasm
What transports the NADH into the matrix?
Malate-Aspartate Shuttle- where energy requirements are relatively low
OR
Glyercol-Phosphate Shuttle
How many ATP is made from NADH using the malate-Aspartate shuttle?
3 ATP per NADH
Describe the malate-Aspartate shuttle
Transporters for Aspartate out the matrix into the cytosol and malate into the matrix from the cytosol.
Cycle of Aspartate to malate ( which moves into matrix) the malate to aspartate ( which moves into the cytosol)
Aspartate<=> Oxaloactate<=> Malate
w/ Transaminase and alpha-ketoglutarate-> glutamate
AND Malate dehyrogenase and NADH + H+ -> NAD+
Describe the glycerol-phosphate
Electrons from NADH used to reduce Dihydroxyacetone phosphate to glycerol 3 phosphate via Cytoplasmic glyercol-3-phosphate dehydrogenase
DHAP can go into glycolysis
When is the Glycerol-phosphate shuttle and malate-Aspartate shuttle used?
Glycerol-phosphate shuttle is for metabolically active tissues eg neurons or muscles
malate-Aspartate SHuttle is for low energetic tissues eg liver
How many ATP is produced in glycerol-phosphate shuttle
Cycle produces FADH2 so 2 ATP per NADH
Compare the 2 shuttles.
What is their Net ATP ranges
G-P shuttle = 36 ATP
M-A shuttle= 38 ATP
Compare the 2 shuttles. How many ATP are gained from the conversion of glyucose to pyruvate and the reoxidation of the 2 NADH produced
G-P shuttle = 6 ATP
M-A shuttle= 8 ATP
What are the major sources of NADH/FADH2?
Glycolysis
TCA cycle
Beta-oxidation of fatty acids
Where is FADH2 made?
FADH2 is made on the inner membrane
Succinate -> fumarate
The succinate dehydrogenase sits in this membrane and is also a component of the electron transport chain
How does pyruavte enter the inter mitochondrial space
MPC
Mitochondrial pyruvate carrier
Are oxidative reactions exergonic or endogenic?
Exergonic
What reaction is coupled to the energy generated as electrons passed from NADH/FADH2?
What does this reaction generate
Coupled to transport of H+ from to mitochondrial matrix to the intermembranous space via the ATP Synthase which aids the production of ATP
this generates an electrochemical gradient across the highly impermeable inner membrane
What does the electrochemical gradient consist of?
Electrochemical gradient has an electrical (charge separation) and a chemical (concentration gradient) component
What is direct transfer of electrons to oxygen not used?
What happens instead?
This would produce too much energy to be used all at once.
So electrons are transferred from one acceptors to another, releasing some energy at each stage
the work is used to pump protons across the membrane and the electrochemical gradient is used to generate ATP
What is the final acceptor on oxidative phosphorylation?
Oxygen
2H+ +2 e + 1/2 O2 -> H2O
Describe the structure and function of a proton pump
Greater [H+] in the intermembranous space than the matrix
In the matrix there is a high affinity binding site with -Ve charges from aa side chains.
The opening and closing of the gates as well as the conformational change required to release the H+ from its site is driven by the energy of the electron transfer.
Now the affinity is low hence H+ release.
How many complexes are in the ETC?
5
Describe Complex I
What is its other names?
What is its role?
What is this accompanied by?
Also called NADH ubiquinone reductase or NADH-Q reductase
It oxidises NADH and transfers 2 electrons to the mobile carrier ubiquinone.
This is accompanied by the transfer of approximately 4 protons across the inner mitochondrial membrane.
Reduced ubiquinone, called ubiquinol (QH2), is free to move throughout the inner membrane.
QH2 next delivers its electrons to complex III (NOT complex II).
Describe Complex II
What is its other names?
What is its role?
Called Q-cytochrome-c oxidoreductase
Complex III transfers the electrons between two mobile electron carrier.
It receives them from QH2 and transfers them to soluble cytochrome-c , located in the intermembraneous space.
1 electron is transferred to 1 cytochrome-c with the transfer of approx. 2H+. Thus there are a total of 4H+ transferred.
Describe Complex IV
What is it also called?
What is its role?
What it is accompanied by?
Also called cytochrome oxidase
This transfers the two electrons from the cytochrome-c proteins to the mitochondrial matrix.
This is accompanied by the transfer of 2 protons to the intermembraneous space and reducing oxygen on the matrix side to produce H2O.
The oxidation of one NADH results in the transfer of aprrox how many H+ to the intermembranous space
10 H+
Where does the oxidation of FADH2 occur?
Which complexes?
What is this also known as?
Complex II,III,IV
Also known as succinate dehydrogenase or succinate-Q reductase.
FADH2 to FAD produces how many ATP?
2 ATP
Describe the structure of the ATP Synthase
Head is a heterohexamer made up of 3 Alpha and 3 beta subunits.
Central rotator stalk (gamma subunit) has a protrusion. As this rotates it moves the alpha and beta domains in a conformational change.
What is the L and T and O state of ATP synthase?
L=loose state- binds ADP and Pi tightly
T=tight state- binds ATP more tightly than ADP
O = open state- can bind ATP or ADP loosly
What is the role of the alpha and gamma subunits in ATP synthase
Alpha- can bind ATP but dont participate in catalysis.
Gamma- rotation interconverts the T L and O states of the 3 Beta subunits
How does ATP synthase work?
H+ passage makes gamma subunit spin between T L and O state which binds ATP, stabilises transition state for phosphoanhydride bond formation and releases ATP
What requires the energy in the synthesis of ATP?
It is not the synthesis of ATP but the unbinding that requires energy
True or False
1) ATP cannot be stored only made on demand
2) ATP is the fuel within a cell and between cells
3) ATP is made all the time
4) ATP needs specific transporters?
1- true
2- false only within the cell
3- false only when it is needed
4- true
What drives ATP/ADP movement?
It is the voltage gradient that drives ATP/ADP movement as -4 charge on ATP prefers to move out while the -3 ADP moves into the matrix.
What happens when there is no demand for energy?
ATP not hydrolysed so ADP levels low
Low ADP means H+ cannot return to mitro. matrix and ATP stuck in the matrix
