RESPIRATION & COUPLED REACTIONS

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) © 2010 Paul Billiet ODWSODWS

Natural Electron ACCEPTORS Pyridine nucleotides Nicotinamide Adenine Dinucleotide (NAD) Flavine Adenine Dinucleotide (FAD) Cytochromes Conjugate proteins which contain a haem group. The iron atom undergoes redox reactions NB The iron atom in the haem group of haemoglobin does not go through a redox reaction Haemoglobin is oxygenated or deoxygenated NAD + + 2H + + 2e - NADH + H + Reduction Oxidation Fe 3+ + e - Fe 2+ Reduction Oxidation © 2010 Paul Billiet ODWSODWS

OXIDATIVE PHOSPHORYLATION A series of REDOX REACTIONS using electron acceptor/donor molecules coupled to glycolysis and the Kreb's 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 © 2010 Paul Billiet ODWSODWS

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 © 2010 Paul Billiet ODWSODWS

Cytochrome c Cytochrome a.a 3 2e - +ve Redox potential -ve Reaction co-ordinate 2e - Flavoprotein/Cytochrome b NAD + NADH + H + FAD FADH 2 1 / 2 O 2 + 2H + H2OH2O  G= kJ  G= kJ  G=- 51 kJ © 2010 Paul Billiet ODWSODWS

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 / 2 O 2  H 2 O © 2010 Paul Billiet ODWSODWS

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 m 2 g -1 mitochondria Heart muscle 200 to 250 m 2 g -1 mitochondria © 2010 Paul Billiet ODWSODWS

The importance of the inner membrane Insect flight muscle x Image Credit: Open University S Hurry (1965) Murray Mouse cardiac muscle Image Credit: Open University S Hurry (1965) Murray

MATRIX The Mechanism of Oxidative phosphorylation: THE CHEMIOSMOTIC PUMP Intermembrane space Outer membrane ATP synthetase ADP + Pi e-e- H+H+ H+H+ H+H+ H+H+ O2O2 2H 2 O ATP Inner membrane © 2010 Paul Billiet ODWSODWS

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 © 2010 Paul Billiet ODWSODWS

THE CHEMIOSMOTIC PUMP IN CHLOROPLASTS X Image Credit: Open University S Hurry (1965) Murray X Image Credit: Open University S Hurry (1965) Murray

Thylakoid space Photophosphorylation Stroma ADP + Pi 2H + 2H / 2 O 2 H2OH2O ATP ATP synthetase 2H + 1/2O21/2O2 2e - 2H + NADP + NADPH + + H + Thylakoid membrane 2e - © 2010 Paul Billiet ODWSODWS