Respiration rganisms can be classified based on how they obtain energy: Autotrophs Able to produce their own organic molecules through photosynthesis Heterotrophs Live on organic compounds produced by other organisms All organisms use cellular respiration to extract energy from organic molecules 1
Cellular respiration Cellular respiration is a series of reactions xidized loss of electrons Reduced gain of electron Dehydrogenation lost electrons are accompanied by protons A hydrogen atom is lost (1 electron, 1 proton) 2
Aerobic respiration C 6 H 12 6 + 6 2 6C 2 + 6H 2 Free energy = 686 kcal/mol of glucose Free energy can be even higher than this in a cell This large amount of energy must be released in small steps rather than all at once. 3
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electrons from food 2e Energy released for synthesis High energy Low energy 2H + 1 / 2 2 H 2 4
Cells use to drive endergonic reactions ΔG (free energy) = 7.3 kcal/mol 2 mechanisms for synthesis 1. Substrate-level phosphorylation Transfer phosphate group directly to ADP During glycolysis 2. xidative phosphorylation synthase uses energy from a proton gradient 5
xidation of Glucose The complete oxidation of glucose proceeds in stages: 1. Glycolysis 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain & chemiosmosis 6
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. uter Glycolysis mitochondrial membrane Glucose Intermembrane space Pyruvate Pyruvate xidation Mitochondrial matrix Acetyl-CoA C 2 C 2 Krebs Cycle FADH 2 e NAD + FAD 2 H 2 Inner mitochondrial membrane e e Electron Transport Chain Chemiosmosis Synthase H + 7
Glycolysis Converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons) 10-step biochemical pathway ccurs in the cytoplasm Net production of 2 molecules by substrate-level phosphorylation 2 produced by the reduction of NAD + 8
xidation and Formation Cleavage Priming Reactions Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate xidation Krebs Cycle Electron Transport Chain Chemiosmosis 6-carbon glucose (Starting material) ADP ADP Glycolysis begins with the addition of energy. Two highenergy phosphates (P) from two molecules of are added to the 6-carbon molecule glucose, producing a 6-carbon molecule with two phosphates. P P 6-carbon sugar diphosphate Then, the 6-carbon molecule with two phosphates is split in two, forming two 3-carbon sugar phosphates. P P P i 3-carbon sugar phosphate NAD + NAD + ADP ADP 3-carbon sugar phosphate P i ADP ADP An additional Inorganic phosphate ( P i ) is incorporated into each 3-carbon sugar phosphate. An oxidation reaction converts the two sugar phosphates into intermediates that can transfer a phosphate to ADP to form. The oxidation reactions also yield giving a net energy yield of 2 and 2. 3-carbon pyruvate 3-carbon pyruvate 9
Pyruvate 1,3-Bisphosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate 3-Phosphoglycerate Dihydroxyacetone Phosphate Glyceraldehyde 3-phosphate Fructose 1,6-bisphosphate Fructose 6-phosphate Glucose 6-phosphate Glucose Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate xidation Krebs Cycle Glycolysis: The Reactions Glucose 1 Hexokinase ADP Glucose 6-phosphate CH 2 H CH 2 P Electron Transport Chain Chemiosmosis 2 Phosphoglucose isomerase Fructose 6-phosphate CH 2 P CH 2 H 3 1. Phosphorylation of glucose by. 2 3. Rearrangement, followed by a second phosphorylation. Phosphofructokinase ADP Fructose 1,6-bisphosphate 4 5 Aldolase Isomerase P CH 2 CH 2 P 4 5. The 6-carbon molecule is split into two 3-carbon molecules one G3P, another that is converted into G3P in another reaction. Dihydroxyacetone phosphate NAD+ P i 6 Glyceraldehyde 3- phosphate (G3P) P i NAD+ P CH 2 C CH 2 H H C CHH CH 2 P 6. xidation followed by phosphorylation produces two molecules and two molecules of BPG, each with one high-energy phosphate bond. 7. Removal of high-energy phosphate by two ADP molecules produces two molecules and leaves two 3PG molecules. 1,3-Bisphosphoglycerate (BPG) ADP 3-Phosphoglycerate (3PG) Glyceraldehyde 3-phosphate dehydrogenase 7 Phosphoglycerate kinase 1,3-Bisphosphoglycerate (BPG) ADP 3-Phosphoglycerate (3PG) P C CHH CH 2 C CHH CH 2 P P 8 9. Removal of water yields two PEP molecules, each with a high-energy phosphate bond. 10. Removal of high-energy phosphate by two ADP molecules produces two molecules and two pyruvate molecules. 2-Phosphoglycerate (2PG) H 2 8 Phosphoglyceromutase 9 Enolase 2-Phosphoglycerate (2PG) H 2 C H C CH 2 H C P Phosphoenolpyruvate Phosphoenolpyruvate (PEP) (PEP) C CH 2 P ADP 10 Pyruvate kinase ADP C C 10 Pyruvate Pyruvate CH 3
must be recycled For glycolysis to continue, must be recycled to NAD + by either: 1. Aerobic respiration xygen is available as the final electron acceptor Produces significant amount of 2. Fermentation ccurs when oxygen is not available rganic molecule is the final electron acceptor 11
Fate of pyruvate Depends on oxygen availability. When oxygen is present, pyruvate is oxidized to acetyl-coa which enters the Krebs cycle Aerobic respiration Without oxygen, pyruvate is reduced in order to oxidize back to NAD + Fermentation 12
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pyruvate Without oxygen H 2 NAD + With oxygen C 2 2 Acetaldehyde ETC in mitochondria Acetyl-CoA NAD + Lactate NAD + Krebs Cycle Ethanol 13
Products of pyruvate oxidation For each 3-carbon pyruvate molecule: 1 C 2 Decarboxylation by pyruvate dehydrogenase 1 1 acetyl-coa which consists of 2 carbons from pyruvate attached to coenzyme A Acetyl-CoA proceeds to the Krebs cycle 14
Acetyl Coenzyme A Pyruvate Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate xidation Krebs Cycle Electron Transport Chain Chemiosmosis Pyruvate xidation: The Reaction Pyruvate C 2 NAD + C C CH 3 CoA S CoA C Acetyl Coenzyme A CH 3 15
Krebs Cycle xidizes the acetyl group from pyruvate ccurs in the matrix of the mitochondria Biochemical pathway of 9 steps in three segments 1. Acetyl-CoA + oxaloacetate citrate 2. Citrate rearrangement and decarboxylation 3. Regeneration of oxaloacetate 16
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate xidation CoA- (Acetyl-CoA) CoA FADH 2 Krebs Cycle Electron Transport Chain Chemiosmosis 4-carbon molecule (oxaloacetate) 6-carbon molecule (citrate) NAD + NAD + C 2 Pyruvate from glycolysis is oxidized Krebs Cycle into an acetyl group that feeds into the Krebs cycle. The 2-C acetyl group combines with 4-C oxaloacetate to produce the 6-C compound citrate (thus this is also called the citric acid cycle). xidation reactions are combined with two decarboxylations to produce, C 2, and a new 4-carbon molecule. Two additional oxidations generate another and an FADH 2 and regenerate the original 4-C oxaloacetate. FADH 2 4-carbon molecule FAD 4-carbon molecule Krebs Cycle 4-carbon molecule 5-carbon molecule C 2 NAD + ADP + P 17
Krebs Cycle For each Acetyl-CoA entering: Release 2 molecules of C 2 Reduce 3 NAD + to 3 Reduce 1 FAD (electron carrier) to FADH 2 Produce 1 Regenerate oxaloacetate 18
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis 1. Reaction 1: Condensation Pyruvate xidation 2 3. Reactions 2 and 3: Isomerization 4. Reaction 4: The first oxidation FADH 2 Krebs Cycle 5. Reaction 5: The second oxidation 6. Reaction 6: Substrate-level phosphorylation Electron T ransport Chain Chemiosmosis 7. Reaction 7: The third oxidation 8 9. Reactions 8 and 9: Regeneration of oxaloacetate and the fourth oxidation Krebs Cycle: The Reactions Acetyl-CoA CoA xaloacetate (4C) C CH 3 C S Citrate (6C) Malate (4C) C H CH CH 2 NAD + 9 Malate dehydrogenase C CH 2 C 1 CoA-SH Citrate synthetase C CH 2 H C C CH 2 C C 2 H 2 8 Fumarase Aconitase 3 Fumarate (4C) C CH HC C Isocitrate (6C) C CH 2 H CH HC C FADH 2 C FAD 7 Succinate (4C) C Succinate dehydrogenase Isocitrate dehydrogenase C 2 4 NAD + CH 2 CH 2 C CoA-SH Succinyl-CoA synthetase Succinyl-CoA (4C) C C 2 -Ketoglutarate (5C) C CH 2 GTP ADP 6 GDP + P i CH 2 CH 2 C S CoA -Ketoglutarate dehydrogenase 5 CoA-SH NAD + CH 2 C C 19
At this point Glucose has been oxidized to: 6 C 2 4 10 These electron carriers proceed to the electron transport chain 2 FADH 2 Electron transfer has released 53 kcal/mol of energy by gradual energy extraction Energy will be put to use to manufacture 20
Electron Transport Chain (ETC) ETC is a series of membrane-bound electron carriers Embedded in the inner mitochondrial membrane Electrons from and FADH 2 are transferred to complexes of the ETC Each complex A proton pump creating proton gradient Transfers electrons to next carrier 21
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate xidation Krebs Cycle Electron Transport Chain Chemiosmosis Mitochondrial matrix H + dehydrogenase bc 1 complex Cytochrome oxidase complex synthase + H + NAD + 2H + + 1 / 2 2 H 2 ADP + P i FADH 2 2 e FAD Inner mitochondrial membrane Intermembrane space 2 e 2 e H + H + a. The electron transport chain Q C H + H + b. Chemiosmosis 22
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 23
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondrial matrix H + ADP + P i Catalytic head Stalk Rotor Intermembrane space H + H + H + H + H + H + 24
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Glucose Pyruvate Pyruvate xidation Acetyl-CoA C 2 e e FADH 2 Krebs Cycle H 2 C 2 2 2H + + 1 / 2 2 H + 32 e Q H + H + C H + 25
Energy Yield of Respiration Theoretical energy yield 38 per glucose for bacteria 36 per glucose for eukaryotes Actual energy yield 30 per glucose for eukaryotes Reduced yield is due to Leaky inner membrane Use of the proton gradient for purposes other than synthesis 26
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose 2 2 Glycolysis Pyruvate 2 5 Chemiosmosis Pyruvate oxidation 2 5 2 Krebs Cycle 6 15 2 FADH 2 3 Chemiosmosis Total net yield = 32 (30 in eukaryotes) 27
xidation Without 2 1. Anaerobic respiration Use of inorganic molecules (other than 2 ) as final electron acceptor Many prokaryotes use sulfur, nitrate, carbon dioxide or even inorganic metals 2. Fermentation Use of organic molecules as final electron acceptor 28
Fermentation Reduces organic molecules in order to regenerate NAD + 1. Ethanol fermentation occurs in yeast C 2, ethanol, and NAD + are produced 2. Lactic acid fermentation ccurs in animal cells (especially muscles) Electrons are transferred from to pyruvate to produce lactic acid 29
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alcohol Fermentation in Yeast Glucose H 2 ADP 2 C G L Y C L Y S I S 2 NAD + 2 H C H CH 3 2 Ethanol H C C CH 3 2 Pyruvate C 2 CH 3 2 Acetaldehyde Lactic Acid Fermentation in Muscle Cells 2 ADP 2 C Glucose G L Y C L Y S I S 2 NAD + 2 C H C H CH 3 2 Lactate C CH 3 2 Pyruvate 30