1. Cellular Respiration Chapter 08

2. Cellular Respiration 2OutlineGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool  Catabolism  Anabolism

3. 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

4. 4 Glucose Breakdown: Summary Reaction

5. 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

6. 6 NAD + Cycle

7. 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

8. 8 Glucose Breakdown: Overview of 4 Phases

9. 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

10. 10 Glycolysis: The Balance Sheet

11. 11 Substrate-level Phosphorylation

12. 12 Glycolysis

13. 13 Glycolysis

14. 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

15. 15 Mitochondrion: Structure & Function

16. 16 Preparatory Reaction

17. 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

18. 18 The Citric Acid Cycle

19. 19 Citric Acid Cycle: Balance Sheet

20. 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

21. 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 +

22. 22 Electron Transport Chain

23. 23 Organization of Cristae

24. 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

25. 25 Overall Energy Yielded per Glucose Molecule

26. 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 +

27. 27 Fermentation

28. 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

29. 29 Products of Fermentation

30. 30 Efficiency of Fermentation InLine Figure 143

31. 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

32. 32 The Metabolic Pool Concept

33. 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

34. 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!

35. 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

36. Cellular Respiration 36ReviewGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool  Catabolism  Anabolism

37. Cellular Respiration Ending Slide Chapter 08