outer membrane inner membrane matrix red = respiratory chain proteins green = ATP synthases Figure 1. Location of enzymes involved in oxidative phosphorylation cytoplasm © OCR 2013

NADH NAD + H+H+ H+H+ H+H+ H+H+ H+H+ and ADP phosphate ATP outer membrane (permeable to H + and has no role in oxidative phosphorylation) inner membrane Krebs cycle matrix cytoplasm H+H+ red = respiratory-chain proteins green = ATP synthase Figure 2. The chemiosmotic theory of oxidative phosphorylation O2O2 H2OH2O electron transport reactions © OCR 2013

NAD + NADH A ox A red Krebs cycle B ox Notes: red = reduced; ox = oxidized The dashed red rectangle is the respiratory chain. The arrows show oxidation/reduction (electron transport) reactions. A, B, C, D are oxidation/reduction components (in reality, there are more). The respiratory chain can also be represented by a series of conventional equations: A red + B ox  A ox + B red B red + C ox  B ox + C red C red + D ox  C ox + D red B red C ox C red D ox D red O2O2 H2OH2O Figure 3. Diagram of a respiratory chain © OCR 2013

inner mitochondrial membrane NADH NAD + UQ O2O2 H2OH2O Complex I Complex IV Complex III cytochrome c UQ = ubiquinone matrix Figure 4. “Stretch and challenge”: further details of the respiratory chain inter-membrane space electron transport reactions red = respiratory chain proteins Note that Complex II is involved in another branch of the respiratory chain which takes electrons from succinate to ubiquinone. It is not shown in this figure. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ © OCR 2013