Cellular Respiration and Fermentation

1. Cellular Respiration and Fermentation Chapter 9

2. Cellular Respiration • In cellular respiration, an organism obtains O2 from the environment and releases CO2 as a waste product • Mitochondria in cells use the CO2 in cellular respiration to break down the sugar and other organic molecules • The energy retrieved from the sugar is used to make ATP

3. Adenine Phosphategroups Hydrolysis Energy Ribose Adenosine diphosphate(ADP) Adenosine triphosphate Figure 5.4A Hydrolysis of ATP • The hydrolysis of adenosine triphosphate (ATP) provides the chemical energy that powers most cell work.

4. P i P Motor protein Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP + ATP P i P P i Solute Solute transported (b) Transport work: ATP phosphorylates transport proteins P NH2 + + NH3 P i Glu Glu Reactants: Glutamic acid and ammonia Product (glutamine) made (c) Chemical work: ATP phosphorylates key reactants How ATP Performs Work

5. Cellular Respiration • Highly reduced molecules • Contains lots of stored chemical energy • Used for long term storage • Needs to be converted to ATP before it is used • Converted to Glucose first

6. Glucose • Glucose is important in cell energy • Cells use glucose to build fats, carbohydrates, and other compounds • Cells recover glucose by breaking down these molecules • Glucose is a high energy molecule

8. Chemical Energy • Potential energy of chemical bonds is the energy of electrons • Position of the electrons • Reduced compounds typically have many C–H bonds with high potential energy. • Oxidized molecules have many C–O bonds with low potential energy. • Glucose is highly reduced

9. Energy of ATP • The electrons in ATP have high potential energy • Negative charges of phosphates repel each other

10. Energy of ATP

11. Energy Coupling • Using the energy of an exergonic reaction to power an endergonic reaction • Glucose gets oxidized and ADP gets reduced to ATP • The complete oxidation of 1 mole of glucose releases 686 kcal of energy.

12. Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Redox Reactions • The movement of electrons from one molecule to another is an oxidation-reduction (redox) reaction • Glucose loses electrons (in H atoms), while O2 gains electrons (in H atoms)

13. Cellular Respiration

14. Overview of Cellular Respiration • Cellular respiration oxidizes sugar and produces ATP in three main stages • Glycolysis occurs in the cytoplasm • The Krebs cycle and the electron transport chain occur in the mitochondria • Glycolysis and Krebs Cycle are exergonic (energy-releasing) • Electron Transport Chain is endergonic (energy using

15. High-energy electrons carried by NADH GLYCOLYSIS ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS KREBSCYCLE Glucose Pyruvicacid Mitochondrion Overview of Cellular Respiration

16. Glycolysis

17. Glycolysis • Series of 10 chemical reactions, is the first step in glucose oxidation • Glucose is broken down into two 3-carbon molecules of pyruvate • Potential energy released is used to phosphorylate ADP • Nicotinamide adenine dinucleotide (NAD+) is reduced to NADH, an electron carrier

18. Glycolysis • Takes place in the cytoplasm • “Splitting of sugar”, starts with 1 molecule of glucose (5C) and ends up with 2 molecules of pyruvic acid (3C) • Produces 2 molecules of ATP and 2 molecules of NADH • Can use ATP immediately, but to use NADH it must pass down the electron transport chain

19. Glucose Pyruvicacid Glycolysis

20. Glycolysis Oxidativephosphorylation Citricacidcycle ATP ATP ATP Energy investment phase Glucose P 2 ATP + 2 used 2 ATP Energy payoff phase formed P 4 ATP 4 ADP + 4 + 2 H+ 2 NADH 2 NAD+ + 4 e- + 4 H + 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NADH 2 NAD+ + 4 e– + 4 H + Glycolysis • Consists of two phases: • Energy investment phase • Uses ATP • Energy payoff phase • Makes ATP and NADH

21. CH2OH H H H H HO HO OH H OH Glucose 4 3 2 5 1 ATP Hexokinase ADP CH2OH P O H H H H OH HO H OH Glucose-6-phosphate Phosphogluco-isomerase CH2O P O CH2OH H HO HO H H HO Fructose-6-phosphate ATP Phosphofructokinase ADP CH2 O O CH2 P P O HO H OH H HO Fructose- 1, 6-bisphosphate Aldolase H O CH2 P Isomerase C O O C CHOH CH2OH O CH2 P Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Glycolysis: Energy Investment Phase • Requires 2 ATP

22. 2 NAD+ Triose phosphate dehydrogenase P i 2 2 NADH + 2 H+ 2 O C O P CHOH P CH2 O 10 8 6 7 9 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP O– 2 C CHOH O P CH2 3-Phosphoglycerate Phosphoglyceromutase O– 2 C O P H C O CH2OH 2-Phosphoglycerate Enolase 2 H2O O– 2 C O P C O CH2 Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP O– 2 C O C O CH3 Pyruvate Glycolysis Energy Payoff Phase • Yields 4 ATP and 2 NADH

23. Citric Acid Cycle

24. Citric Acid Cycle • aka: Krebs Cycle • Takes place in the matrix of the mitochondrion • Completes the oxidation of organic fuel • Oxidates pyruvate • Before entering the citric acid cycle, pyruvate must be converted into Acetyl Coenzyme A • 3 reactions • Produces 1 NADH • Links the cycle to glycolysis

26. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Conversion of Pyruvate to Acetyl CoA

29. Citric Acid Cycle • As pyruvic acid is oxidized released energy is used to: • Reduce NAD+ to NADH; • Reduce flavin adenine dinucleotide (FAD) to FADH2 (another electron carrier); and • Phosphorylate ADP to make ATP. • NADH and FADH are high energy electron carriers

30. Electron Transport Chain

31. Electron Transport Chain • inner mitochondrial membrane of eukaryotes • Oxidative phosphorylation • Glycolysis and the citric acid cycle shuttle the high energy transporters NADH and FADH2 to the machinery of oxidative phosphorylation • Where the Electron transport chain releases that energy to make ATP

32. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b Fe•S 30 Cyt c1 IV Cyt c Free energy (G) relative to O2 (kcl/mol) Cyt a Cyt a3 20 10 0 O2 2 H + + 12 H2O Electron Transport Chain • Series of molecules embedded in the inner membrane

33. Electron Transport Chain • Breaks the fall of electrons down to oxygen into several energy producing steps instead of one big one • Electrons from NADH and FADH2 lose energy in several steps • Carriers are reduced and oxidized ‘downhill’ from carrier to carrier • At the end of the chain electrons are passed to water

34. 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis ofATP 2 H+ + 2 e– ATP ATP H2 + 1/2 O2 Free energy, G Electron transport chain ATP Explosiverelease ofheat and lightenergy 2 e– (a) Uncontrolled reaction Free energy, G 1/2 O2 2 H+ H2O (b) Cellular respiration H2O Electron Transport Chain

35. Chemiosmosis • In the membrane are also protein complexes called ATP synthases. • Makes ATP from ADP and P • Reverse ion pump- uses the energy of an ion gradient to power ATP synthesis • Ion pump uses ATP to pump ions out of or into cell • Uses difference in H+ concentration on sides of inner membrane to run the ATP synthase

36. A rotor within the membrane spins clockwise whenH+ flows past it down the H+ gradient. INTERMEMBRANE SPACE H+ H+ H+ H+ H+ H+ H+ A stator anchoredin the membraneholds the knob stationary. A rod (for “stalk”)extending into the knob alsospins, activating catalytic sites in the knob. H+ Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. ADP + ATP P i MITOCHONDRIAL MATRIX Chemiosmosis

37. Chemiosmosis • At certain steps along the electron transport chain electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space • ATP synthetases are the only sites on the membrane that are permeable to H+ • Chemiosmosis is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work

38. Chemiosmosis

39. Oxidative Phosphorylation • ATP production via the proton-motive force and ATP synthase is called oxidative phosphorylation. ATP synthase produces 26 of the 30 ATP molecules produced per glucose molecule during cell respiration

40. Electron shuttles span membrane MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 FADH2 2 NADH 2 NADH 6 NADH Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA 2 Pyruvate Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol by substrate-level phosphorylation by substrate-level phosphorylation About 36 or 38 ATP Maximum per glucose: Summary of Aerobic Respiration

41. Anaerobic Respiration • Some prokaryotes, especially those in oxygen-poor environments, use other electron acceptors in anaerobic respiration. • Respiration can be run in a limited fashion without oxygen • Lactic acid fermentation • Alcohol fermentation

42. Anaerobic Respiration

43. Fermentation • Oxidative phosphorylation ceases when there is no oxygen • Cellular respiration relies on oxygen to produce ATP • In the absence of oxygen cells can still produce ATP through fermentation • Fermentation gets ATP through glycolysis • Problem is NADH regeneration

44. Fermentation • Glycolysis • Can produce ATP with or without oxygen, in aerobic or anaerobic conditions • Couples with fermentation to produce ATP • Fermentation consists of • Glycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis

45. P1 2 ATP 2 ADP + 2 O – C O C O Glucose Glycolysis CH3 2 Pyruvate 2 NADH 2 NAD+ 2 CO2 H H H C O C OH CH3 CH3 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation Alcoholic Fermentation • In alcohol fermentation • Pyruvate is converted to ethanol in two steps, one of which releases CO2 • Occurs in yeast

46. P1 2 ATP 2 ADP + 2 Glucose Glycolysis O– C O C O 2 NADH 2 NAD+ CH3 O C O H OH C CH3 2 Lactate (b) Lactic acid fermentation Lactic Acid Fermentation • During lactic acid fermentation • Pyruvate is reduced directly to NADH to form lactate as a waste product

47. Cellular Respiration and Other Fuels • Catabolic pathways • Funnel electrons from many kinds of organic molecules into cellular respiration • Most of our diet does not consist merely of glucose • Many fuels must be broken down into their most basic forms first

48. ATP Production • For ATP production, cells first use carbohydrates, then fats, and finally proteins.

49. Biosynthesis • Anabolic pathways • Not all organic materials are used as fuel • Food also provides carbon skeletons for the body to make its own molecules • May come directly from food or through glycolysis or the citric acid cycle

50. Biosynthesis