Cellular Respiration: Harvesting Chemical Energy

Transcription

1 Energy Flows through the Ecosystem Cellular Respiration: Harvesting Chemical Energy Energy enters the ecosystem in form of solar energy Photosynthesis converts solar energy to chemical energy. and O are produced from CO and Cellular respiration converts chemical energy from food to. is oxidized to CO and With each conversion of energy, some energy gets lost as heat ECOSYSTEM CO Sunlight energy Photosynthesis in chloroplasts Cellular respiration in mitochondria (for cellular work) Heat energy +! +! O Redox Reactions (oxidation and reduction simultaneously occur in a chemical reaction) The human body uses energy from for all its activities

2 Cells need! powers active transport Mechanical work (movement) Anabolic (endergonic) reactions Cellular Respiration Cellular Respiration occurs in three stages Mitochondrion Cytosol and other fuel molecules oxidation Acetyl-CoA Citric acid Electrons carried by NADH and FADH Substrate-level Substrate-level Electron transfer system and oxidative oxidation Citric acid Cytosol In glycolysis, glucose is oxidized to pyruvate. The electrons from that reaction reduce NAD + to NADH. Oxidation NADH carries the electrons to be used in the oxidative

3 In and the Citric Acid Cycle, is produced by Substrate Level Phosphorylation The Electron Carrier NAD + can pick up electrons Enzyme P Substrate ADP Substrate Enzyme Product + Product is transported into the mitochondrial matrix as Acetyl-CoA NAD + NADH + H + CoA Acetyl CoA (acetyl coenzyme A) CO Coenzyme A

4 NADH must be red Summary! For glycolysis to continue, NADH must be red to NAD + by either: 1. Aerobic respiration Oxygen is available as the final electron acceptor Produces significant amount of. Fermentation Occurs when oxygen is not available Organic molecule is the final electron acceptor! Converts 1 glucose (6 carbons) to pyruvate (3 carbons)! 10-step biochemical pathway! Occurs in the cytoplasm! Net production of molecules by substratelevel! NADH produced by the reduction of NAD + The needs grooming for the next step is transported into the mitochondrial matrix as Acetyl-CoA oxidation Citric acid Mitochondrial matrix Acetyl-CoA

5 Mitochondria, Sites of Cellular Respiration Acetyl-CoA Summary of Krebs Cycle (Citric Acid Cycle) Reactions! For each Acetyl-CoA entering the Krebs Cycle: molecules of CO are released 3 NAD + are reduced to 3 NADH 1 FAD (electron carrier) is reduced to FADH 1 is produced The initial acceptor molecule Oxaloacetate is regenerated

6 The last step of Cellular Respiration: Phosphorylation Acetyl-CoA oxidation Inner mitochondrial membrane Citric acid Citric acid Phosporylation consists of the Electron transport chain and Chemiosmosis Electron Transport Chain ETC is a series of membrane-bound electron carriers! Embedded in the inner mitochondrial membrane! Electrons from NADH and FADH are transferred to complexes of the ETC! Each complex A proton pump creating proton gradient Transfers electrons to next carrier

7 Why Electron Transport? Free energy, G Free energy, G H H +! O H / O H +! O / O Explosive release Explosive of heat release and light energy Free energy, G (from food via NADH) Controlled release Controlled of H + + e! release of H + + e energy energy for synthesis of Free energy, G Electron transport chain Electron transport chain e! Chemiosmosis! Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion! Membrane relatively impermeable to ions! Most protons can only reenter matrix through synthase Uses energy of gradient to make from ADP + P i (a) Uncontrolled Uncontrolled reaction reaction H + e H + (b) Cellular Cellular respiration respiration! O 1 / O Overview Cellular Respiration Inhibitors of the Electron Transport Chain Rotenone Cyanide, carbon monoxide Oligomycin H + H + H + H + H + H + H + H + H+ Synthase DNP FADH FAD NADH NAD + 1 O +! H + H + H + H + ADP +! P Electron Transport Chain Chemiosmosis

8 Summary:, Citric Acid Cycle and Phosphorylation The Fate of is Dependent on Oxygen Availability CYTOSOL Electron shuttles span membrane NADH or MITOCHONDRION FADH NADH NADH 6 NADH FADH Acetyl CoA Citric acid : electron transport and chemiosmosis about 3 or 34 by substrate-level by substrate-level by oxidation, depending on which shuttle transports electrons form NADH in cytosol The actual yield is about 30 About Maximum per glucose: 36 or 38 per molecule of glucose due to leaky membranes Fermentation occurs when oxygen is not available Alcoholic Fermentation Ethanol Lactate Fermentation replenishes NAD + to further drive

9 Cells use many kinds of organic molecules as fuel for cellular respiration (catabolic processes) Food molecules provide raw materials for biosynthesis (anabolic processes) needed to drive biosynthesis Food, such as peanuts CITRIC ACID CYCLE Acetyl CoA GLUCOSE SYNTHESIS G3P Carbohydrates Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Amino groups Amino acids Fatty acids Glycerol Sugars Proteins Fats Carbohydrates G3P Acetyl GLYCOLYSIS CoA CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Cells, tissues, organisms