Transcript Chapter 8
Catabolic Pathways and Production of ATP • C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP + heat) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 e– + 2 H+ NAD+ 2 e– + H+ H+ NADH Dehydrogenase + 2[H] (from food) Nicotinamide (oxidized form) + Nicotinamide (reduced form) H+ • NADH passes the electrons to the electron transport chain • Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction • Oxygen pulls electrons down the chain in an energy-yielding tumble • The energy yielded is used to regenerate ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H2 + 1/2 O2 + 2H 1 /2 O2 1/2 O2 (from food via NADH) Explosive release of heat and light energy Free energy, G Free energy, G 2 H+ + 2 e– Controlled release of energy for synthesis of ATP ATP ATP ATP 2 e– 2 H+ H2O Uncontrolled reaction H2O Cellular respiration Electrons carried via NADH and FADH2 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation 1. Glycolysis harvests energy by oxidizing glucose to pyruvate • Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases: – Energy investment phase – Energy payoff phase Animation: Glycolysis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. The citric acid cycle completes the energyyielding oxidation of organic molecules • Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix • The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn Animation: Electron Transport Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 9-10 MITOCHONDRION CYTOSOL NAD+ NADH + H+ Acetyl Co A Pyruvate Transport protein CO2 Coenzyme A 3. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food • These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy investment phase Glucose 2 ATP used 2 ADP + 2 P Glycolysis Citric acid cycle Oxidative phosphorylation Energy payoff phase ATP ATP ATP 4 ADP + 4 P 2 NAD+ + 4 e– + 4 H+ 4 ATP formed 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+ 2 Pyruvate + 2 H2O 2 ATP 2 NADH + 2 H+ ATP Yield From Complete Oxidation of Glucose Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NADH 50 Free energy (G) relative to O2 (kcal/mol) FADH2 40 FMN I Multiprotein complexes FAD Fe•S II Fe•S Q III Cyt b 30 Fe•S Cyt c1 Glycolysis Citric acid cycle ATP ATP Oxidative phosphorylation: electron transport and chemiosmosis IV Cyt c Cyt a Cyt a3 20 10 0 2 H+ + 1/2 O2 H2O ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The electron transport chain generates no ATP • The chain’s function is to break the large freeenergy drop from food to O2 into smaller steps that release energy in manageable amounts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis • The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work Animation: Fermentation Overview Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Proteins Carbohydrates Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Fats Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation Major Metabolic Sites Liver Muscle, Nerve etc Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings