JacobBob
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Which part from the electrons moving through an etc to chemiosmosis is oxidative phosphorylation ? Which part exactly I mean ?
When the mark scheme says no oxidative phosphorylation occurs , which part do they mean ?
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Reality Check
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What level is this? A Level or undergrad.

The phosphorylation occurs when the protons pumped out by the respiratory chain flow back into the matrix through ATP synthase (sometimes known as Complex V). Proton flow isn't actually needed for ATP synthesis; it's needed to release the ATP from the synthase.
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You also need to be more specific about the question you're being asked. 'Which part do they mean' is a bit ambiguous!
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JacobBob
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A level
And here’s a picture of the question+Mark scheme
Also , isn’t the diffusion of H+ back to the matrix known as chemiosmosis ? If not, then what is it ? Name:  6F47A380-515A-46C1-9142-C76335AFE471.jpeg
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(Original post by Reality Check)
What level is this? A Level or undergrad.

The phosphorylation occurs when the protons pumped out by the respiratory chain flow back into the matrix through ATP synthase (sometimes known as Complex V). Proton flow isn't actually needed for ATP synthesis; it's needed to release the ATP from the synthase.
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Cytochrome oxidase is the final electron acceptor, where oxygen is reduced to water. Inhibiting this enzyme prevents aerobic ATP production because electrons cannot be passed on from cytochrome c. Note that ATP could still be produced via anaerobic glycolysis (this is point 5 on the mark scheme).

The chemiosmotic theory, as it relates to protons being pumped out of the mitochondrial matrix providing an electrochemical proton motive force which enables ATP 'synthesis' is not directly relevant to the question. You're not being asked about the inhibition of ATP synthase, nor about the complexes which pump protons out of the matrix. Hence why it doesn't appear as a correct answer in the mark scheme. You're being asked about the inhibition of the final electron acceptor in the ETC, which is cytochrome c oxidase. However, where it is relevant is in by inhibiting the final electron acceptor, further electron flow through the ETC is prevented, which then prevents protons being pumped out by other complexes in the ETC to form the proton motive force which then prevents ATP 'synthesis' via ATP synthase.

Does that make sense?
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searching123job
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https://www.ncbi.nlm.nih.gov/books/NBK22388/#_A2533_
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JacobBob
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I understand the first part
But I’m not sure I understand what you’re talking about in the 2nd part
Do you mean that chemiosmosis is not allowed in the mark scheme because the question does not ask about ATP synthase inhibition ?

And I’m confused about what oxidative phosphorylation is after all 😅

(Original post by Reality Check)
Cytochrome oxidase is the final electron acceptor, where oxygen is reduced to water. Inhibiting this enzyme prevents aerobic ATP production because electrons cannot be passed on from cytochrome c. Note that ATP could still be produced via anaerobic glycolysis (this is point 5 on the mark scheme).

The chemiosmotic theory, as it relates to protons being pumped out of the mitochondrial matrix providing an electrochemical proton motive force which enables ATP 'synthesis' is not directly relevant to the question. You're not being asked about the inhibition of ATP synthase, nor about the complexes which pump protons out of the matrix. Hence why it doesn't appear as a correct answer in the mark scheme. You're being asked about the inhibition of the final electron acceptor in the ETC, which is cytochrome c oxidase. However, where it is relevant is in by inhibiting the final electron acceptor, further electron flow through the ETC is prevented, which then prevents protons being pumped out by other complexes in the ETC to form the proton motive force which then prevents ATP 'synthesis' via ATP synthase.

Does that make sense?
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(Original post by JacobBob)
I understand the first part
But I’m not sure I understand what you’re talking about in the 2nd part
Do you mean that chemiosmosis is not allowed in the mark scheme because the question does not ask about ATP synthase inhibition ?

And I’m confused about what oxidative phosphorylation is after all 😅
OK, I'll try to break it down for you simply. Oxidative phosphorylation is where high energy electrons from the breakdown of substrates like glucose and fatty acids in the diet are used in redox reactions in a succession of protein complexes. The electrons are passed on from special carriers (have you heard of NADH and FADH2?) where they finally reduce oxygen to water. This happens at the final complex in the ETC, cytochrome c oxidase (which is the complex you're being asked about in the question). On their journey from NADH/FAD2 to the final acceptor, some of the energy is harnessed to pump protons out of the matrix of the mitochondria into the intermembranal space. This causes an electrochemical gradient to be established, separated by the inner mitochondrial membrane based on both charge and concentration. These protons flow back to the -ve matrix via channel in ATP synthase and, in doing so, enable the release of ATP from the synthase (this is the correct version: more often it is simplified to 'proton flow results in ATP synthesis).

So far so good? Too detailed? Generally unhelpful?
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(Original post by JacobBob)
Do you mean that chemiosmosis is not allowed in the mark scheme because the question does not ask about ATP synthase inhibition ?
Just to answer this - yes, sort of. The focus of the question is on what happens when you prevent electrons flowing through the ETC, which is what happens if you disable cyt c oxidase. The proton motive force here is irrelevant - it's a bit like putting the cart before the horse. If there's no electron flow through the ETC, then the proton-pumping complexes can't pump protons and it's not even a consideration. Does that make sense?
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JacobBob
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(Original post by Reality Check)
Just to answer this - yes, sort of. The focus of the question is on what happens when you prevent electrons flowing through the ETC, which is what happens if you disable cyt c oxidase. The proton motive force here is irrelevant - it's a bit like putting the cart before the horse. If there's no electron flow through the ETC, then the proton-pumping complexes can't pump protons and it's not even a consideration. Does that make sense?
Yes, THANK YOU.
Are you a biology teacher or professor .. or doctor maybe ?
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