chapter_8_powerpoint_le.ppt - Chapter 0 8 Cellular Respirat ion Outline Glycolysis Transition Reaction Citric Acid Cycle Electron Transport System

chapter_8_powerpoint_le.ppt - Chapter 0 8 Cellular Respirat...

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Unformatted text preview: Chapter 0 8 Cellular Respirat ion Outline Glycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool Catabolism Anabolism Cellular Res piration 2 Cellular Respiration Cellular Res piration 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 3 Glucose Breakdown: Summary Reaction 4 NAD+ and FAD Cellular Res piration 5 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 FADH2 NAD+ Cycle 6 Cellular Respiration: Overview of 4 Phases Cellular Res piration 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 7 Glucose Breakdown: Overview of 4 Phases 8 Glucose Breakdown: Glycolysis Cellular Res piration 9 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 Glycolysis: The Balance Sheet 10 Substrate-level Phosphorylation 11 Glycolysis 12 Glycolysis 13 Cellular Res 14 Glucose Breakdown: piration 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+ CO2 released, and transported out of mitochondria into the cytoplasm Mitochondrion: Structure & Function 15 Preparatory Reaction 16 Glucose Breakdown: The Citric Acid Cycle Cellular Res piration A.K.A. Krebs cycle Occurs in matrix of mitochondria Both acetyl (C2) groups received from the preparatory reaction: Join with an enzyme CoA molecule to make acetylCoA Acetyl (C2) group transferred to oxaloacetate (C2) to make citrate (C6) Each acetyl oxidized to two CO2 molecules Remaining 4 carbons from oxaloacetate converted back to oxaloacetate (thus “cyclic”) NADH, FADH2 capture energy rich electrons ATP formed by substrate-level phosphorylation 17 The Citric Acid Cycle 18 Citric Acid Cycle: Balance Sheet 19 Electron Transport Chain Cellular Res piration 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 & FADH2 Produce ATP by oxidative phosphorylation 20 Electron Transport Chain Cellular Res piration 21 The fate of the hydrogens: Hydrogens from NADH deliver enough energy to make 3 ATPs Those from FADH2 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 O2 not present, NADH cannot release H No longer recycled back to NAD+ Electron Transport Chain 22 Organization of Cristae 23 Glucose Catabolism: Overall Energy Yield Cellular Res piration 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 24 Overall Energy Yielded per Glucose Molecule 25 Fermentation (1) Cellular Res piration 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+ 26 Fermentation 27 Fermentation (2) Cellular Res piration 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 O2 can be obtained Anaerobic exercise Lactic acid accumulates Causes cramping and oxygen debt When O2 restored, lactate broken down to acetyl-CoA and metabolized 28 Products of Fermentation 29 Efficiency of Fermentation InLine­Figure­143 30 Metabolic Pool: Catabolism (1) Cellular Res piration 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 31 The Metabolic Pool Concept 32 Metabolic Pool: Catabolism (2) Cellular Res piration 33 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 (NH2 removed) in liver Results in poisonous ammonia (NH3) Quickly converted to urea ­ Different R-groups from AAs processed differently ­ Fragments enter respiratory pathways at many different points Metabolic Pool: Anabolism (1) Cellular Res piration 34 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! Metabolic Pool: Anabolism (2) Cellular Res piration 35 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 – transamination 2 ­ However, other amino acids (9) cannot be synthesized by humans Essential amino acids Must be present in diet or die Review Glycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool Catabolism Anabolism Cellular Res piration 36 Ending Slide Chapter 08 Cellular Respirat ion ...
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