ATP synthase Flashcards
what is the structure of the F1 ATP synthase?
flattened sphere consisting of alternating a and B subunits arranged like segments of orange. the polypeptides that make up the stalk are asymmetrically arranged
what are the three B subunits of ATP synthase?
- B-ATP
- B-ADP
- B-empty
what is the structure of the F0 ATP synthase?
composed of a, b and c subunits. the c subunits are small, hydrophobic polypeptides with 2 TM regions. these form a rising which rotates perpendicular to the membrane
outline the binding change mechanism
1- B-ADP binds ADP and Pi from the surrounding medium
2-this causes the B subunit to change conformation to the B-ATP form which binds ATP tightly and stabilises it
3-this brings about equilibrium of ADP +Pi and ATP on the surface
4-the subunit changes to B-empty, and the low affinity for ATP causes newly synthesised aATP to be released
how is the binding change mechanism driven?
passage of protons through the F0 pore causes the cylinder of c subunits and attached Y subunits to rotate.
with each rotation of 120 degrees, Y comes into contact with a different B subunit, the three B subunits interact in such a way that when a subunit assumes empty conformation, the surrounding Bs must assume B-ATP and B-ADP
what is predicted via the binding-change mechanism?
the Y subunit should rotate in one direction when F1F0 is synthesising ATP and a different direction when the enzyme is hydrolysing ATP
how was the rotation of the Y subunit shown experimentally?
- fluorescent actin polymer was attached to Y
- movement was watched relative to a3B3 under a microscope when ATP was hydrolysed
- when the entire F1F0 complex was tested, the ring of c subunits rotated with Y
outline the model for proton flow through the F0 complex?
1- proton enters half channel on P side
2- proton displaces Arg210 the the adjacent c subunit
3- arg rotates, displacing H+ from Asp
4- displaced H+ exits on N side
5- c10 ring rotates, Arg returns to P side half channel
6- process repeats
which four observations developed Mitchell’s hypothesis of H+ gradient driven synthesis of ATP?
1- pH in the mitochondrial inter membrane space is 1 unit lower than in the matrix
2- ATP is synthesised by mitochondria when a pH gradient is imposed, even when no electron transport occurs
3- both respiratory chain and ATP synthesis reactions are vectorially organised, orientation of the carriers matters
4- compounds that carry protons across the inner membrane such as uncouplers, dissipate the proton gradient, preventing ATP synthesis
how is proton motive force generated?
chemical potential (deltapH, inside is alkaline) + electrical potential (inside is negative) -> ATP synthesis driven by proton motive force
what is meant by the term ‘chemiosmotic coupling’?
there is an obligate connection between mitochondrial ATP synthesis and electron flow through the respiratory chain, neither process can exist without the other
why do cyanide and carbon monoxide block ATP synthesis?
these are inhibitors of the passage of electrons to O2, and the energy of substrate oxidation is required to drive ATP synthesis in mitochondria
how does oligomycin inhibit respiration?
blocks flow of protons into the matrix via ATP synthase. this means there is no path for return of protons to the matrix, the proton gradient builds until the energy cost of pumping protons out of the matrix equals or exceeds energy released by transfer of electrons from NADH to O2
what are DNP and FCCP?
chemical uncouplers - weak acids with hydrophobic properties that permit them to diffuse readily across mitochondrial membranes, where they can release a proton to dissipate the proton gradient
what is a prediction of the chemiosmotic theory?
an artificially created gradient should be able to replace electron transfer in driving ATP synthesis
