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Cellular Respiration Chapter 08
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Cellular Respiration 2OutlineGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool Catabolism Anabolism
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Cellular Respiration 3 A cellular process that requires oxygen and gives off carbon dioxide Usually involves breakdown of glucose to carbon dioxide and water Energy extracted from glucose molecule: Released step-wise Allows ATP to be produced efficiently Oxidation-reduction enzymes include NAD + and FAD as coenzymes
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4 Glucose Breakdown: Summary Reaction
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Cellular Respiration 5 NAD + and FAD NAD + (nicotinamide adenine dinucleotide) Called a coenzyme of oxidation-reduction it can Oxidize a metabolite by accepting electrons Reduce a metabolite by giving up electrons Each NAD + molecule used over and over again FAD (flavin adenine dinucleotide) Also a coenzyme of oxidation-reduction Sometimes used instead of NAD + Accepts two electrons and two hydrogen ions (H + ) to become FADH 2
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6 NAD + Cycle
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Cellular Respiration 7 Cellular Respiration: Overview of 4 Phases Glycolysis: Occurs in cytoplasm Glucose broken down to two molecules of pyruvate ATP is formed Transition reaction: Both pyruvates are oxidized Electron energy is stored in NADH Two carbons are released as CO 2 Citric acid cycle: Electron energy is stored in NADH and FADH 2 ATP is formed Four carbons are released as CO 2 Electron transport chain: Extracts energy from NADH & FADH 2 Produces 32 or 34 molecules of ATP
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8 Glucose Breakdown: Overview of 4 Phases
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Cellular Respiration 9 Glucose Breakdown: Glycolysis Occurs in cytoplasm outside mitochondria Energy Investment Steps: Two ATP are used to activate glucose Glucose splits into two G3P molecules Energy Harvesting Steps: Two electrons (as hydrogen atoms) are picked up by two NAD + Four ATP produced by substrate-level phosphorylation Net gain of two ATP Both G3Ps converted to pyruvates
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10 Glycolysis: The Balance Sheet
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11 Substrate-level Phosphorylation
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12 Glycolysis
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13 Glycolysis
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Cellular Respiration 14 Glucose Breakdown: The Preparatory (Prep) Reaction End product of glycolysis, pyruvate, enters the mitochondrial matrix Pyruvate converted to 2-carbon acetyl group Attached to Coenzyme A to form acetyl-CoA Electron picked up (as hydrogen atom) by NAD + CO 2 released, and transported out of mitochondria into the cytoplasm
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15 Mitochondrion: Structure & Function
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16 Preparatory Reaction
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Cellular Respiration 17 Glucose Breakdown: The Citric Acid Cycle A.K.A. Krebs cycle Occurs in matrix of mitochondria Both acetyl (C 2 ) groups received from the preparatory reaction: Join with an enzyme CoA molecule to make acetyl- CoA Acetyl (C 2 ) group transferred to oxaloacetate (C 2 ) to make citrate (C 6 ) Each acetyl oxidized to two CO 2 molecules Remaining 4 carbons from oxaloacetate converted back to oxaloacetate (thus “cyclic”) NADH, FADH 2 capture energy rich electrons ATP formed by substrate-level phosphorylation
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18 The Citric Acid Cycle
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19 Citric Acid Cycle: Balance Sheet
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Cellular Respiration 20 Electron Transport Chain Location: Eukaryotes: cristae of the mitochondria Aerobic Prokaryotes: plasma membrane Series of carrier molecules: Pass energy rich electrons along Complex arrays of protein and cytochromes Cytochromes are respiratory molecules Complex carbon rings with metal atoms in center Receives electrons from NADH & FADH 2 Produce ATP by oxidative phosphorylation
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Cellular Respiration 21 Electron Transport Chain The fate of the hydrogens: Hydrogens from NADH deliver enough energy to make 3 ATPs Those from FADH 2 have only enough for 2 ATPs “Spent” hydrogens combine with oxygen Recycling of coenzymes increases efficiency Once NADH delivers hydrogens, it returns (as NAD + ) to pick up more hydrogens However, hydrogens must be combined with oxygen to make water If O 2 not present, NADH cannot release H No longer recycled back to NAD +
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22 Electron Transport Chain
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23 Organization of Cristae
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Cellular Respiration 24 Glucose Catabolism: Overall Energy Yield Net yield per glucose: From glycolysis – 2 ATP From citric acid cycle – 2 ATP From electron transport chain – 32 ATP Energy content: Reactant (glucose) 686 kcal Energy yield (36 ATP) 263 kcal Efficiency 39%; balance is waste heat
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25 Overall Energy Yielded per Glucose Molecule
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Cellular Respiration 26 Fermentation (1) When oxygen limited: Spent hydrogens have no acceptor NADH can’t recycle back to NAD + Glycolysis stops because NAD + required Fermentation: “Anaerobic” pathway Can provide rapid burst of ATP Provides NAD + for glycolysis NADH combines with pyruvate to yield NAD +
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27 Fermentation
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Cellular Respiration 28 Fermentation (2) Pyruvate reduced by NADH to: Lactate Animals & some bacteria Cheese & yogurt; sauerkraut Ethanol & carbon dioxide Yeasts Bread and alcoholic beverages Allows glycolysis to proceed faster than O 2 can be obtained Anaerobic exercise Lactic acid accumulates Causes cramping and oxygen debt When O 2 restored, lactate broken down to acetyl-CoA and metabolized
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29 Products of Fermentation
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30 Efficiency of Fermentation InLine Figure 143
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Cellular Respiration 31 Metabolic Pool: Catabolism (1) Foods: Sources of energy rich molecules Carbohydrates, fats, and proteins Catabolism (breakdown side of metabolism) Breakdown products enter into respiratory pathways as intermediates Carbohydrates Converted into glucose Processed as above
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32 The Metabolic Pool Concept
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Cellular Respiration 33 Metabolic Pool: Catabolism (2) Breakdown products enter into respiratory pathways as intermediates (cont.) Proteins Broken into amino acids (AAs) Some AAs used to make other proteins Excess AAs deaminated (NH 2 removed) in liver Results in poisonous ammonia (NH 3 ) Quickly converted to urea Different R-groups from AAs processed differently Fragments enter respiratory pathways at many different points
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Cellular Respiration 34 Metabolic Pool: Anabolism (1) All metabolic reactions part of metabolic pool Intermediates from respiratory pathways can be used for anabolism Anabolism (build-up side of metabolism): Carbs: Start with acetyl-CoA Basically reverses glycolysis (but different pathway) Fats G3P converted to glycerol Acetyls connected in pairs to form fatty acids Note – dietary carbohydrate RARELY converted to fat in humans!
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Cellular Respiration 35 Metabolic Pool: Anabolism (2) Anabolism (cont.): Proteins: Made up of combinations of 20 different amino acids Some amino acids (11) can be synthesized from respiratory intermediates organic acids in citric acid cycle can make amino acids Add NH 2 – transamination However, other amino acids (9) cannot be synthesized by humans Essential amino acids Must be present in diet or die
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Cellular Respiration 36ReviewGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool Catabolism Anabolism
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Cellular Respiration Ending Slide Chapter 08
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