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Lecture notes of 8 pages for the course Membrane and cellular Biochemistry at QMUL
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ATP SYNTHASELearning objectives:
1. Describe the overall structure and subunits composition of ATP synthase
2. Explain the functional roles of the F 1 and F0 domains of ATP synthase
3. Outline and explain the experiments that showed these functions
4. Explain the binding change mechanism of ATP SYNTHESIS
5. Discuss how the structure of the F1 head can be used to explain the mechanism of ATP synthesis by ‘’rotational catalysis’’
6. Explain how rotation of the central stalk was shown experimentally
7. Explain the mechanism of coupling between proton translocation through F 0 and ATP synthesis by F1
What we know about ATPase comes from prokaryote cells and not eukaryote cell.
Believed ATPase to be present before membrane but for this course believe that membranes came about first
The Krebs cycle
all the reactions in the Krebs cycle is an enzyme catalysed reaction
Citric acid is found in lemonade and orange juice
Kerb cycle and urea cycle are connected by the aspartate shunt
There are a few wheels (molecular machines that go around) in nature.
- i.e. ATP synthase & bacterial flagella
The machinery for ATP formation: F1
Nearly all enzymes catalyse equilibrium reactions (reactants to products).
Isolated spherical particles (coupling factor 1, F1) catalyse ATP hydrolysis: F1 is an ATPase
Hydrolysis of ATP by F1 is a reversible reaction:
Reversibility of ATPases: even the Na+/K+ ATPase can catalyse ATP synthesis
, How does the Na+/K+ ATPase pump work
- Na+/K+ pump is an ATPase, which uses chemical energy to energise the plasma membrane
- Sodium ions bind to Na+/K+ ATPase pump from the cytosol and potassium ions are released into cytosol
- ATP hydrolysis results in change in conformation
- Sodium ion released into the ECF and potassium ions bind again
How to drive ATP synthesis
- If potassium inside and sodium outside the cell are very high (non-physiological)
- Then ion gradient can drive ATP synthesis by the Na +/K+ ATPase pump.
Even the Na+/K+ ATPase physiologically and biologically only hydrolysis ATP but if push the equilibrium far enough, Na +/k+
ATPase will synthesis ATP
Usually enzymes can catalyse ATP hydrolysis and synthesis depending on where the equilibria is
Na+/K+ ATPase can convert proton motive force into ATP or hydrolyse ATP to generate a proton gradient
Experiments with sub mitochondrial particles demonstrated that F1 is required for ATP formation and F0 is a proton
channel
Experiment connected both ATPase to proton motive force and ATP synthesis
Mitochondria broken up into little particles
- If disrupt cellular membranes it will form vesicles inside out
- If provide the vesicles with NADH and cytochrome c will run the respiratory ETC and can measure a proton
motive force is generated (pumping proton into vesicles). Can add ADP to measure synthesis of ATP
- If treat the vesicles with urea, the F1 groups will be knocked off the ATPase and can no longer synthesis ATPase
and don’t generate a proton gradient if have NADH or cytochrome c
- The ATPase is not involved in proton gradient generation
The structure of the ATP synthase
Spherical F1 head
- F1 contain five subunits with a composition of α 3β3δ γε
There are 3 betas and 3 alphas arranged sequentially (1 alpha 1 beta)
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