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Outline. Glycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool Catabolism Anabolism. Cellular Respiration. A cellular process that requires oxygen and gives off carbon dioxide

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Outline

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  1. Cellular Respiration

  2. Outline • Glycolysis • Transition Reaction • Citric Acid Cycle • Electron Transport System • Fermentation • Metabolic Pool • Catabolism • Anabolism

  3. Cellular Respiration • 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

  4. Glucose Breakdown:Summary Reaction

  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 FADH2

  6. NAD+ Cycle

  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 CO2 • Citric acid cycle: • Electron energy is stored in NADH and FADH2 • ATP is formed • Four carbons are released as CO2 • Electron transport chain: • Extracts energy from NADH & FADH2 • Produces 32 or 34 molecules of ATP

  8. Glucose Breakdown:Overview of 4 Phases

  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

  10. Glycolysis:The Balance Sheet

  11. Substrate-level Phosphorylation

  12. Glycolysis

  13. Glycolysis

  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+ • CO2 released, and transported out of mitochondria into the cytoplasm

  15. Mitochondrion:Structure & Function

  16. Preparatory Reaction

  17. Glucose Breakdown:The Citric Acid Cycle • 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 acetyl-CoA • 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

  18. The Citric Acid Cycle

  19. Citric Acid Cycle:Balance Sheet

  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 & FADH2 • Produce ATP by oxidative phosphorylation

  21. Electron Transport Chain • 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+

  22. Electron Transport Chain

  23. Organization of Cristae

  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

  25. Overall Energy Yieldedper Glucose Molecule

  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+

  27. Fermentation

  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 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

  29. Products of Fermentation

  30. Efficiency of Fermentation InLine Figure 143

  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

  32. The Metabolic Pool Concept

  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 (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

  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!

  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 NH2 – transamination • However, other amino acids (9) cannot be synthesized by humans • Essential amino acids • Must be present in diet or die

  36. Review • Glycolysis • Transition Reaction • Citric Acid Cycle • Electron Transport System • Fermentation • Metabolic Pool • Catabolism • Anabolism

  37. Cellular Respiration

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