RESPIRATION & COUPLED REACTIONS © 2016 Paul Billiet ODWS

THE ELECTRON TRANSPORT CHAIN (ETC) Coupling the oxidation of food to the synthesis of ATP Oxidation Is a Loss of electrons (OIL) Reduction Is a Gain of electrons (RIG) © 2016 Paul Billiet ODWS

Natural Electron ACCEPTORS Pyridine nucleotides Nicotinamide Adenine Dinucleotide (NAD) Flavine Adenine Dinucleotide (FAD) NAD+ + 2H+ + 2e- NADH + H+ Reduction Oxidation Cytochromes Conjugate proteins which contain a haem group. The iron atom undergoes redox reactions Fe3+ + e- Fe2+ Reduction Oxidation NB The iron atom in the haem group of haemoglobin does not go through a redox reaction Haemoglobin is oxygenated or deoxygenated © 2016 Paul Billiet ODWS

OXIDATIVE PHOSPHORYLATION A series of REDOX REACTIONS using electron acceptor/donor molecules coupled to glycolysis and the Krebs cycle The electron acceptors/donors reduce (when receiving electrons) And oxidise (when losing electrons) one another along an ELECTROCHEMICAL GRADIENT Each molecule in the series has a lower REDOX POTENTIAL than the one before. © 2016 Paul Billiet ODWS

Down the chain If this energy release is > 30.5 kJ mol-1 a mole of ATP can be synthesised from ADP by a coupled reaction The first molecule in the series is NAD (or FAD), a COENZYME of various DEHYDROGENASE enzymes [NAD (oxidised)  NADH + H+ (reduced)] Next come a series of iron containing proteins called CYTOCHROMES. © 2016 Paul Billiet ODWS

+ve Redox potential -ve Reaction co-ordinate NAD+ NADH + H+ FAD FADH2 2e- G=- 51 kJ Flavoprotein/Cytochrome b 2e-  G=- 38.5 kJ Cytochrome c Cytochrome a.a3  G=- 84.5 kJ 2e- 1/2O2 + 2H+ H2O © 2016 Paul Billiet ODWS

The electron transport chain Electrons are produced by splitting hydrogen atoms taken from the food molecules (H  H+ + e-) by dehydrogenases The last electron acceptor in the series is OXYGEN Thus at the end of the ETC: 2H+ + 2e- + 1/2O2  H2O © 2016 Paul Billiet ODWS

The location of the ETC The mitochondrial inner membrane of eukaryotes(the plasma membrane of prokaryotes) Surface area increased by CRISTAE Numbers of cristae = activity of cell e.g. Liver cell 40 m2 g-1 mitochondria Heart muscle 200 to 250 m2 g-1 mitochondria. © 2016 Paul Billiet ODWS

The importance of the inner membrane Insect flight muscle x 42 000 Open University S Hurry (1965) Murray Mouse cardiac muscle Open University S Hurry (1965) Murray © 2016 Paul Billiet ODWS

The Mechanism of Oxidative phosphorylation: THE CHEMIOSMOTIC PUMP Outer membrane The Mechanism of Oxidative phosphorylation: THE CHEMIOSMOTIC PUMP Inner membrane MATRIX e- H+ H+ H+ O2 2H2O ADP + Pi H+ ATP synthetase ATP Intermembrane space © 2016 Paul Billiet ODWS

Electron tomography used to produce images of active mitochondria. © 2016 Paul Billiet ODWS

The Mechanism: THE CHEMIOSMOTIC PUMP The ETC creates a concentration gradient by pumping H+ out of the mitochondrial inner matrix As these H+ diffuse back into the matrix across the inner membrane they drive ATP synthesis. © 2016 Paul Billiet ODWS

THE CHEMIOSMOTIC PUMP IN CHLOROPLASTS X 22 000 Open University S Hurry (1965) Murray X 80 000 Open University S Hurry (1965) Murray © 2016 Paul Billiet ODWS

Photophosphorylation NADPH+ + H+ NADP+ Stroma 2H+ 2e- 2e- 2e- 2H+ H2O 2H+ + 1/2O2 1/2O2 Thylakoid space 2H+ 2H+ Thylakoid membrane ATP synthetase ADP + Pi ATP 2H+ © 2016 Paul Billiet ODWS