ATP Synthase Flashcards
Where is ATP synthase located and what happens when the mitochondria is damaged?
Located in inner mitochondria membrane
Damaged mitochondria: Proton gradient is decoupled, ATP hydrolysis occurs
In intact mitochondria supplied with NADH and oxygen, ATP is synthesised= Will continue ATP synthesis if proton gradient is supplied
What is the structure of ATP synthase?
Transmembrane complex + Multiple amphipathic helical subunits
2 major components:
1) F1 ATPase= water-soluble globular complex in matrix= ATP hydrolysis or synthesis site
2) Fo= Coupling factor, proton channel spanning the membrane
Part of FoF1 complex can rotate= C-ring thats embedded into the membrane is going to rotate in the membrane
Proton enters the matrix and every time one proton moves, C ring rotates and move round once= Part of F1
How is the rotation and ATP synthesis linked?
Beta-subunits of the alpha3beta3 hexametric assembly of F1 actually carry out the catalysis= Bit on the end of F1 in the matrix
Rotation of the of the gamma subunit (Axel, stalk in the middle of the hexametric assembly and C-ring)= relative to the 3 beta subunits changes their conformation
- Axel rotates= 3 distinct faces
- Depending on which face of the axel you’ve got, a conformational change occurs on the alpha-beta subunit
- Goes tom Tight conformation (catalyses ADP + Pi ATP + H2O) —> Open (Can bind or release ATP/ ADP + Pi) –> Loose (contains bound ADP + Pi)
Tight conformation is energetically unfavourable process as they both have negative charges
BASICALLY: The catalysis of ATP synthesis happens in F1 hexameric assembly, the rotation of the C ring can change its faces so that it a different part of the process is carried out
There is a movie showing the rotation on the powerpoint- Slide 60
How is the rotation of the rotor part of F0F1 complex carried out?
- H+ enters a subunit down a half channel & protonates an aspartic acid on a c subunit
- At the same time, an aspartic acid on the next c subunit is released to matrix via 2nd half channel
- Electrostatic charge (as H+ and aspartic acid is normally negative)= Forces movement of c ring with respect to alpha subunit
- Repeated= Causes the c ring to rotate with respect to alpha= Forces gamma to rotate with respect to an alphabeta hexamer
What toxins can block oxidative phosphorylation?
3 types: 1) Interference of electron flow 2) Interference of proton flow 3) Miscellaneous compounds Cyande, CO, Azide= Interact with cytochrome C which blocks= Cannot generate proton force
2,4-DNP= Uncoupling agent as they stop ATP synthesis but electrons transport still continues= Oxygen is consumed. They are lipid-soluble small molecules that can bind H+ ions and transport them across the membranes= Electron transport occurs but some DNP carries H+ ions back into mitochondrion= No proton gradient= Energy released as heat
What do transporters do?
ATP synthesised in mitochondrial matrix BUT most of usage is in cytosol= ATP/ADP translocase= Take 1 molecule of ADP binding on the outer side of mitochondrial membrane and exchange for ATP
It can replenish supply of ADP needed for synthesis of ATP
Phosphate transporter: Symporter with phosphate and uses proton to drive uptake of phosphate= Need phosphate uptake to generate ATP (DO not include that ATP in calculations)
Why is the glycerol phosphate shuttle needed?
Inner mitochondrial membrane= Impermeable to NADH
=NADH produced in the cytoplasm during glycolysis must be reoxidised (NAD+) using a membrane shuttle= Combination of enzyme reactions that bypass this impermeability barrier
Dihydroxyacetone phosphate in cytosol —-> reduced—> Glycerol 3-phosphate
NADH —> Oxidised —> NAD+
By: Cytosolic glycerol 3-phosphate dehydrogenase
THEN:
Glycerol 3-phosphate diffuses across the inner mitochondrial membrane where it is converted back to dihydroxyacetone phosphate by mitochondrial glycerol 3-phosphate dehydrogenase= Uses FADH NOT NADH, and is then deoxidised by transferring electrons to ubiquinone
The dihydroxyacetone phosphate then diffuses back to cytosol
Where is the glycerol phosphate shuttle especially active?
In striated muscle
Enables high rate of oxidative phosphorylation
What is the malate-aspartate shuttle?
In heart and liver:
Cytosolic NADH can be reoxidised via malate-aspartate shuttle:
1) Aspartate can be converted to oxaloacetate in the cytosol using alpha-ketoglutarate to be converted to glutamate
2)Oxaloacetate is then converted to malate by cytoplasmic malate dehydrogenase which reoxidises NADH to NAD+
2) Malate enters the mitochondrion via malate-alpha-ketoglutarate carrier in inner mitochondrial membrane
3) Matrix: Malate is reoxidised to oxaloactate by NAD+
Why it is important?
It is a way of converting amino acids into oxaloactate which is one of the rate limiting steps in the citric acid cycle
What is respiratory control?
-Mitochondria can only oxidise FADH2 and NADH as long as there is ADP and Pi available
-Electron flow ceases if ATP is not produced
-Actual rate of oxidative phosphorylation is set by the availability of ADP= If ADP is added= rate of oxygen consumption increases= ATP is made
-If ADP concentration falls, electron transport slows down
ENSURES: Electron flow occurs ONLY when ATP synthesis is required
Oxidative phosphorylation is regulated by ATP consumption
What happens in brown fat mitochondria?
-Brown fat= Specialised to produce heat
-High levels of mitochondria= Haem pigments= Brown
-Thermogenesis: Production of heat by uncoupling, brown fat contains thermogenic protein= Allows H+ ions to flow back into mitochondria without having to enter via ATP synthase= Uncouples electron transport and oxidative phosphorylation= Generates heat from the energy released by NADH oxidation
-Newborns have brown fat in sensitive body areas= Heat production= Provides protection from cold conditions
Also could play role in maintaining body temperature in hibernating animals
