AS OCR Biology: Oxidative Phosphorylation and Chemiosmosis

AS OCR Biology: Oxidative Phosphorylation and Chemiosmosis

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Oxidative Phosphorylation and Chemiosmosis
The final stage of aerobic respiration:
Oxidative Phosphorylation
It takes place within the intermembrane space of the mitochondria, where there
are cristae increasing the surface area for electron carriers and ATP synthase.
Reduced NAD and FAD, from the Krebs cycle, are oxidised when they donate
hydrogen atoms, which are split into H+ and electrons.
In the process of Oxidative Phosphorylation;
The first electron carrier is called NADH Dehydrogenase
The protons go into the matrix
Oxidative Phosphorylation is also known as The electron transport chain
o As electrons flow along the electron transport chain, energy is released and used by
proteins such as NADH Dehydrogenase (Protein I) and Cytochrome C (Protein IV) to
pump protons across intermembrane space into the matrix.
o This builds up a proton gradient, which is also a pH gradient and an
electrochemical gradient.
o This means potential energy builds up in the intermembrane space.
o The H+ cannot diffuse through the lipid part of the inner membrane space but can
diffuse through ion channels. These proteins are associated with the ATP Synthase.
This flow of protons is chemiosmosis.
Oxidative Phosphorylation
Oxidative Phosphorylation is the formation of ATP by the addition of inorganic
phosphate (Pi) to ADP (Adenine Diphosphate) in the presence of oxygen.
Oxidation of coenzymes NADH (at the NADH Dehydrogenase) and FADH (at
Protein II)
o The oxidation of NADH causes a release of 2e-, used by the protein to pump
H+, but also it releases 2H+
o The oxidation of FADH causes a release of 2e- and 2H+

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Electrons flow along the electron transport chain. This provides energy for the
active transport of protons(Chemiosmosis)
Dehydrogenas Protein II CARRIER Protein III CARRIER Cytochrome ATP
e (Intrinsic) (Extrinsic) Ubiquinone (Intrinsic) Cytochrome C Oxidase Synthase
(2e- per go) (1e- per go) (intrinsic) (intrinsic)
1. NADH oxidised at NADH Dehydrogenase
1.1. 2e- released and used to pump protons; 2H+ released
2. FADH oxidised at Protein II
2.1. 2e- released and 2H+ released
3. Ubiquinone carries all 4e- to Protein III
4.…read more

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In Oxidative Phosphorylation,
On average, for every NADH molecule, 2.5 ATP molecules are produced.
On average, for every FADH molecule, 1.5 ATP molecules are produced.
Stages of
Name of Molecule Total ATP
Respirati produced
Glycolysis Link Krebs
Reaction Cycle
NADH 2 2 6 10 x 2.5 = 25
FADH 0 0 2 2 x 1.5 = 3
A total of 28 ATP molecules are produced from Oxidative Phosphorylation, using solely
the oxidisation of NADH and FADH.
Recall, for each glucose molecule:
I.…read more

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The same case
happens with Aspartate.
1. Oxygen is the final molecule the electrons bind to and are stable. This then is the end of
oxidative phosphorylation, and so respiration.
2. The proton gradient produces a pH gradient, also known as electrochemical gradient. The
accumulation of H+ is seen as potential energy as their movement can be used, and is used,
to drive a process of chemiosmosis.
3.…read more


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