Ch. 9 Cellular Respira,on BIOL Energy Arrives as sunlight Photosynthesis Energy ECOSYSTEM Light energy Plants capture sunlight organic molecules and generates O Carbs used in cellular respira@on CO + H O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O Cells use energy stored in organic molecules to regenerate powers most cellular work Heat energy Energy eventually leaves as heat Catabolic Pathways and Produc,on of The breakdown of organic molecules is exergonic Aerobic respira,on Consumes organic molecules and O and yields Fermenta,on Typically glucose Par@al degrada@on of sugars that occurs without O Anaerobic respira,on similar to aerobic respira@on but uses compounds other than O as the final electron acceptor
Cellular Respira,on Cellular respira,on includes both aerobic and anaerobic respira@on but is ogen used to refer to aerobic respira@on 3 of 4 macromolecule classes may be used as fuel carbohydrates, fats, and proteins C 6 H O 6 + 6 O 6 CO + 6 H O + Energy ( + heat) oxida@on reduc@on reac@ons The Principle of Redox Chemical reac@ons that transfer electrons between reactants are called Oxida,on redox reac,ons a substance loses electrons Reduc,on is oxidized becomes oxidized (loses electron) becomes reduced (gains electron) a substance gains electron OIL RIG is reduced (the amount of posi@ve charge is reduced) Reducing agent The Principle of Redox electron donor Oxidizing agent electron receptor Reactants becomes oxidized Products becomes reduced Some redox rxns do not transfer electrons Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water but change the electron sharing in covalent bonds example is the reac@on between methane and O
Oxida,on During Cellular Respira,on During cellular respira@on, the fuel (such as glucose) is oxidized, and O is reduced: becomes oxidized becomes reduced NAD + and the Electron Transport Chain and other organic molecules Broken down in a series of steps NAD + (nico@namide adenine dinucleo@de) Electron carrier Electrons from organic compounds transferred func@ons as an oxidizing agent during cellular respira@on NADH Reduced form of NAD + represents stored energy that is used to synthesize Dehydrogenase Fig. 9 4 e + H + e + H + Dehydrogenase NADH H + NAD + + [H] Reduction of NAD + Oxidation of NADH Nicotinamide (reduced form) + H + Nicotinamide (oxidized form)
Free energy, G NADH NAD+ and the Electron Transport Chain Delivers electrons to the electron transport chain (ETC) ETC passes electrons in a series of steps instead of one explosive reac@on Slow, controlled energy release O receives electrons from the ETC AGer an energy yielding tumble down the chain Final electron acceptor Free energy, G H + / O H O Explosive release of heat and light energy (a) Uncontrolled reaction H + / O (from food via NADH) H + + e Electron transport chain e (b) Cellular respiration Controlled release of energy for synthesis of H + H O / O The energy yielded is used to regenerate The Stages of Cellular Respira,on: A Preview Cellular respira@on has three stages: Glycolysis Literally sugar breaking breaks down glucose into two molecules of pyruvate Citric acid cycle completes the breakdown of glucose Also called Krebs cycle Oxida,ve phosphoryla,on accounts for most of the synthesis Includes Electron Transport Chain Fig. 9 6 Electrons carried via NADH Glycolysis Cytosol Substrate-level
Fig. 9 6 Electrons carried via NADH Electrons carried via NADH and FADH Glycolysis Citric acid cycle Cytosol Mitochondrion Substrate-level Substrate-level Fig. 9 6 3 Electrons carried via NADH Electrons carried via NADH and FADH Glycolysis Citric acid cycle Oxidative : electron transport and chemiosmosis Cytosol Mitochondrion Substrate-level Substrate-level Oxidative Oxida,ve Phosphoryla,on Oxida,ve phosphoryla,on accounts for almost 90% of the generated by cellular respira@on 3 of 36 38 total substrate level phosphoryla,on formed in glycolysis and the citric acid cycle Enzyme Enzyme P Substrate + Product
Glycolysis Glycolysis Breaks down glucose into two molecules of pyruvate Occurs in the cytoplasm Two major phases: Energy investment phase Energy payoff phase Fig. 9 8 Energy investment phase + P used Energy payoff phase 4 + 4 P 4 formed NAD + + 4 e + 4 H + NADH + H + + H O Net + H O 4 formed used NAD + + 4 e + 4 H + NADH + H + Fig. 9 9 Hexokinase -6-phosphate Hexokinase -6-phosphate
Fig. 9 9 Fig. 9 9 Hexokinase Phosphoglucoisomerase Phosphoglucoisomerase -6-phosphate Fructose-6-phosphate -6-phosphate Fructose-6-phosphate Fig. 9 9 3 Fig. 9 9 3 Hexokinase Phosphoglucoisomerase Phosphofructokinase 3 Phosphofructokinase Fructose-, 6-bisphosphate -6-phosphate Fructose-6-phosphate Fructose-, 6-bisphosphate 3 Fructose-6-phosphate 3 Fig. 9 9 4 Fig. 9 9 4 Hexokinase -6-phosphate Phosphoglucoisomerase Fructose-6-phosphate Phosphofructokinase Fructose-, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 3 4 5 Aldolase Isomerase Fructose-, 6-bisphosphate Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 4 5
Fig. 9 9 5 NAD + NADH + H + 6 P i NAD + Glyceraldehyde- 3-phosphate 6 NADH P i + H + Fig. 9 9 6 NAD + 6 NADH P i + H + 7 Phosphoglycerokinase 3-Phosphoglycerate 3-Phosphoglycerate Fig. 9 9 7 NAD + 6 NADH P i + H + 7 Phosphoglycerokinase 3-Phosphoglycerate 8 Phosphoglyceromutase -Phosphoglycerate 3-Phosphoglycerate 7 Phosphoglycerokinase 8 Phosphoglyceromutase -Phosphoglycerate
Fig. 9 9 8 NAD + NADH + H + 6 P i 7 Phosphoglycerokinase 3-Phosphoglycerate -Phosphoglycerate 8 Phosphoglyceromutase -Phosphoglycerate 9 Enolase H O H O 9 Enolase Phosphoenolpyruvate Phosphoenolpyruvate Fig. 9 9 9 NAD + NADH + H + 6 P i 7 Phosphoglycerokinase 3-Phosphoglycerate 8 Phosphoglyceromutase Phosphoenolpyruvate 0 kinase -Phosphoglycerate 9 Enolase H O Phosphoenolpyruvate 0 kinase If O is present pyruvate enters the mitochondrion Intermediate Step CYTOSOL MITOCHONDRION NAD + NADH + H + acetyl CoA Two per original glucose Transport protein 3 CO Coenzyme A Acetyl CoA added to coenzyme A becomes acetyl coa As it crosses the mito membranes Yields first CO wastes Reduces a NAD+ to NADH Enters the citric acid cycle
Citric Acid Cycle Citric acid cycle Also called the Krebs cycle NAD + NADH CO CoA Occurs in the mitochondrial matrix + H + Acetyl CoA CoA CoA Cycle oxidizes organic fuel derived from pyruvate Citric acid cycle CO generates, 3 NADH, and FADH per turn FADH FAD + P i 3 NAD + 3 NADH + 3 H + Twice per glucose! Citric acid cycle Citric Acid Cycle Eight steps Each catalyzed by a specific enzyme Acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate Forming citrate Coenzyme A returns to intermediate step The next seven steps decompose the citrate back to oxaloacetate Makes the process a cycle The NADH and FADH Deliver electrons to the electron transport chain