Aerobic Respiration

Topic 8.2: AEROBIC RESPIRATION Redox Reactions Glycolysis Biological energy can be stored or released by redox reactions • Oxidation is the Loss of electrons / hydrogen (OIL) • Reduction is the Gain of electrons / hydrogen (RIG) Aerobic respiration is preceded by glycolysis (anaerobic) • Glucose is broken down to form two pyruvate molecules Oxidation Reduction Electrons Loss Gain Hydrogen Loss Gain Oxygen Gain Loss The process of glycolysis involves four basic stages: • Glucose is phosphorylated by ATP (becomes less stable) • The 6C sugar splits (lysis) into two triose phosphates (3C) • 3C sugars are oxidised to form reduced carriers (NADH) • A small amount of ATP is produced (net gain = 2 ATP) Electron carriers transfer chemical energy via redox reactions • Organic molecules are oxidised to form reduced carriers • The reduced carriers may then be oxidised to form ATP 2 NAD+ 2 ATP OIL RIG Glucose Pyruvate (×2) GLYCOLYSIS 4 ATP 2 NADH Aerobic Respiration Link Reaction: • Pyruvate transported from cytosol to mitochondrial matrix • Pyruvate oxidised to produce a reduced carrier (NADH) • Pyruvate decarboxylated to form acetyl CoA (CO2 produced) Krebs Cycle: • Acetyl CoA is combined with a 4C compound (forms 6C) • 6C compound broken down into original 4C (CO2 produced) • This involves oxidation reactions (NADH / FADH2 formed) • There is also a small yield of ATP (one per cycle) Electron Transport Chain: • Reduced carriers are oxidised at the electron transport chain • The energy is used to make ATP (via oxidative phosphorylation) • 32 ATP molecules are made from the reduced carriers Glycolysis (CYTOSOL) Glucose 2 4 ATP 2 NADH 4 ATP 2 NADH 6 ATP 2 ATP 6 NADH 18 ATP 2 FADH2 4 ATP ATP Pyruvate 2× Acetyl-CoA Krebs Cycle Substrate level phosphorylation Oxidative phosphorylation Total net yield: 36 Oxidative Phosphorylation • Carrier molecules donate electrons (oxidation) to an electron transport chain located on the mitochondrial cristae • The electrons lose energy as they are passed along the chain, which is used to pump protons (H+ ions) from the matrix • The build up of protons in the intermembrane space creates an electrochemical gradient (proton motive force) • Protons return to the matrix via a transmembrane enzyme (ATP synthase), which uses the translocation to make ATP • The de-energised electrons are removed from the chain by oxygen (final electron acceptor), forming water as a by-product Intermembrane Space: High [ H+ ] H+ H+ H+ e- eNADH ATP H+ H2O O2 H+ Mitochondrial Matrix: Low [ H+ ]