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+ AP Biology Mrs. Valdes Chapter 9: Cellular Respiration: Harvesting Chemical Energy.

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Presentation on theme: "+ AP Biology Mrs. Valdes Chapter 9: Cellular Respiration: Harvesting Chemical Energy."— Presentation transcript:

1 + AP Biology Mrs. Valdes Chapter 9: Cellular Respiration: Harvesting Chemical Energy

2 + Overview: Life Is Work Living cells require energy from outside sources Herbivore: giant panda, obtain energy by eating plants Carnivore: hyena eats other animals Omnivore: squirrel eats insects and seeds and chicken legs?

3 + Energy flows into ecosystem as sunlight and leaves as heat Photosynthesis  O 2 &organic molecules (used in cellular respiration) Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work

4 + Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels MULTIPLE processes central to cellular respiration and related pathways Breakdown of organic molecules is exergonic Cellular respiration: includes both aerobic and anaerobic respiration; often used to refer to aerobic respiration Aerobic respiration: consumes organic molecules and O 2 ; yields ATP Anaerobic respiration: similar to aerobic respiration but consumes compounds other than O 2 Fermentation: partial degradation of sugars that occurs without O 2 Carbohydrates, fats, and proteins all consumed as fuel, however it is helpful to trace cellular respiration with the sugar glucose: C 6 H 12 O O 2  6 CO H 2 O + Energy (ATP + heat) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5 + Redox Reactions: Oxidation and Reduction Transfer of electrons during chemical reactions releases energy stored in organic molecules used to synthesize ATP Redox reactions: oxidation-reduction reactions; chemical reactions that transfer electrons between reactants Oxidation: substance loses electrons, or is oxidized Reduction: substance gains electrons, or is reduced (the amount of positive charge is reduced) REMEMBER: OIL-RIG Oxidation Is Loss Reduction Is Gain

6 + Fig. 9-UN1 becomes oxidized (loses electron) becomes reduced (gains electron)

7 + Reducing agent: electron donor Oxidizing agent: electron receptor is called the Some redox reactions do not transfer electrons but change electron sharing in covalent bonds Ex: reaction between methane and O 2

8 + Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration, the fuel (such as glucose) is oxidized, and O 2 is reduced: Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9 + Stepwise Energy Harvest via NAD + and the Electron Transport Chain Cellular respiration: glucose & other organic molecules broken down in a series of steps NAD + : Electrons from organic compounds usually first transferred to NAD +, a coenzyme functions as oxidizing agent during cellular respiration NADH: reduced form of NAD + represents stored energy that is tapped to synthesize ATP NADH passes electrons to electron transport chain passes electrons in series of steps instead of one EXPLOSIVE reaction O 2 pulls electrons down chain in an energy-yielding tumble Energy yielded is used to regenerate ATP

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11 + Fig. 9-5 Free energy, G (a) Uncontrolled reaction H2OH2O H / 2 O 2 Explosive release of heat and light energy (b) Cellular respiration Controlled release of energy for synthesis of ATP 2 H e – 2 H + 1 / 2 O 2 (from food via NADH) ATP 1 / 2 O 2 2 H + 2 e – Electron transport chain H2OH2O

12 + The Stages of Cellular Respiration: A Preview Three stages: Glycolysis: breaks down glucose into two molecules of pyruvate Citric acid cycle: completes the breakdown of glucose Oxidative phosphorylation: accounts for most of the ATP synthesis

13 + Fig Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH

14 + Fig Mitochondrion Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH Substrate-level phosphorylation ATP Electrons carried via NADH and FADH 2 Citric acid cycle

15 + Fig Mitochondrion Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH Substrate-level phosphorylation ATP Electrons carried via NADH and FADH 2 Oxidative phosphorylation ATP Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis

16 + Oxidative phosphorylation: process that generates most of the ATP powered by redox reactions accounts for almost 90% of the ATP generated by cellular respiration Substrate-level phosphorylation: produces smaller amount of ATP in glycolysis and the citric acid cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ATP Production

17 + Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis or “splitting of sugar” breaks down glucose into two molecules of pyruvate Glycolysis occurs in the cytoplasm and has two major phases: Energy investment phase Energy payoff phase

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19 + Glycolysis Consists of series of chemical reactions catalyzed by specific enzymes Takes place in cytosol of cell Four main steps 6-C glucose  Two 3-C pyruvic acid one six-carbon molecule of glucose is oxidized to produce TWO three-carbon molecule of pyruvic acid

20 + Step 1 Two phosphate groups attached to glucose forming new 6-C compound Phosphate groups supplied by two ATP molecules 2 ATP used  2 ADP

21 + Step 2 6-C compound split into 2 PGAL molecules

22 + Step 3 Both PGAL molecules are oxidized and receive phosphate group 2 NADH  2 NAD+ Product: New 3-C compound

23 + Step 4 Phosphate groups added in Steps 1&3 removed from 3-C compounds formed in Step 3 THUS! we get 2 pyruvic acid molecules Each phosphate group is added to ADP to give us ATP!!!!!!!!! Total: 4 ATP

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25 + Let’s talk numbers... Two ATP used in Step 1 Four ATP produced in Step 4 Net Yield: Two ATP

26 + Fig ATP ADP Hexokinase 1 ATP ADP Hexokinase 1 Glucose Glucose-6-phosphate Glucose Glucose-6-phosphate

27 + Fig Hexokinase ATP ADP 1 Phosphoglucoisomerase 2 Phosphogluco- isomerase 2 Glucose Glucose-6-phosphate Fructose-6-phosphate Glucose-6-phosphate Fructose-6-phosphate

28 + 1 Fig Hexokinase ATP ADP Phosphoglucoisomerase Phosphofructokinase ATP ADP 2 3 ATP ADP Phosphofructo- kinase Fructose- 1, 6-bisphosphate Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose- 1, 6-bisphosphate Fructose-6-phosphate 3

29 + Fig Glucose ATP ADP Hexokinase Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP ADP Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Aldolase Isomerase Fructose- 1, 6-bisphosphate Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 4 5

30 + Fig NAD + NADH H + 2 2P i Triose phosphate dehydrogenase 1, 3-Bisphosphoglycerate 6 2 NAD + Glyceraldehyde- 3-phosphate Triose phosphate dehydrogenase NADH2 + 2 H + 2 P i 1, 3-Bisphosphoglycerate 6 2 2

31 + Fig NAD + NADH 2 Triose phosphate dehydrogenase + 2 H + 2 P i 2 2 ADP 1, 3-Bisphosphoglycerate Phosphoglycerokinase 2 ATP 2 3-Phosphoglycerate ADP 2 ATP 1, 3-Bisphosphoglycerate 3-Phosphoglycerate Phosphoglycero- kinase 2 7

32 + Fig Phosphoglycerate Triose phosphate dehydrogenase 2 NAD + 2 NADH + 2 H + 2 P i 2 2 ADP Phosphoglycerokinase 1, 3-Bisphosphoglycerate 2 ATP 3-Phosphoglycerate 2 Phosphoglyceromutase 2-Phosphoglycerate Phosphoglycero- mutase

33 + Fig NAD + NADH H + Triose phosphate dehydrogenase 2 P i 1, 3-Bisphosphoglycerate Phosphoglycerokinase 2 ADP 2 ATP 3-Phosphoglycerate Phosphoglyceromutase Enolase 2-Phosphoglycerate 2 H 2 O Phosphoenolpyruvate Phosphoglycerate Enolase 2 2 H 2 O Phosphoenolpyruvate 9

34 + Fig Triose phosphate dehydrogenase 2 NAD + NADH ADP 2 ATP Pyruvate Pyruvate kinase Phosphoenolpyruvate Enolase 2 H 2 O 2-Phosphoglycerate Phosphoglyceromutase 3-Phosphoglycerate Phosphoglycerokinase 2 ATP 2 ADP 1, 3-Bisphosphoglycerate + 2 H ADP 2 ATP Phosphoenolpyruvate Pyruvate kinase 2 Pyruvate 10 2 P i

35 + Energy Yield Kilocalorie- 1,000 calories; often unit used to measure energy Complete oxidation on ONE glucose molecule= 686 kcal One ADP  One ATP absorbs 12 kcal Can you calculate the efficiency of glycolysis? 2 ATP produced Percent usually a calculation x100

36 + Efficiency of Glycolysis

37 + What does that mean?! Two ATP molecules produces during glycolysis only use small percentage of energy that could be released from glucose SO! anaerobic pathways are NOT very efficient Probably evolved before aerobic pathways

38 + Concept 9.3: The citric acid cycle completes energy-yielding oxidation of organic molecules In presence of O 2, pyruvate enters the mitochondrion Before citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis Citric acid cycle also called the Krebs cycle takes place within the mitochondrial matrix oxidizes organic fuel derived from pyruvate, generating… 1 ATP 3 NADH 1 FADH 2 per turn

39 + Fig Pyruvate NAD + NADH + H + Acetyl CoA CO 2 CoA Citric acid cycle FADH 2 FAD CO NAD H + ADP +P i ATP NADH

40 + Eight steps, each catalyzed by a specific enzyme Acetyl group of acetyl CoA joins cycle by combining with oxaloacetate, forming citrate Acetyl CoA + Oxaloacetate = Citrate Next seven steps decompose the citrate back to oxaloacetate, making the process a cycle NADH and FADH 2 produced by cycle relay electrons extracted from food to the electron transport chain Citric Acid Cycle

41 + Fig Acetyl CoA Oxaloacetate CoA—SH 1 Citrate Citric acid cycle

42 + Fig. 9-UN6 Inputs Outputs Acetyl CoA ATP NADH FADH 2 Oxaloacetate Citric acid cycle S—CoA CH3CH3 C O O C COO CH 2 COO

43 + Fig Acetyl CoA Oxaloacetate Citrate CoA—SH Citric acid cycle 1 2 H2OH2O Isocitrate

44 + Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Citric acid cycle Isocitrate NAD + NADH + H +  -Keto- glutarate CO2CO2

45 + Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Isocitrate NAD + NADH + H + Citric acid cycle  -Keto- glutarate CoA—SH NAD + NADH + H + Succinyl CoA CO2CO2 CO2CO2

46 + Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Isocitrate NAD + NADH + H + CO2CO2 Citric acid cycle CoA—SH  -Keto- glutarate CO2CO2 NAD + NADH + H + Succinyl CoA CoA—SH GTP GDP ADP P i Succinate ATP

47 + Fig Acetyl CoA CoA—SH Oxaloacetate H2OH2O Citrate Isocitrate NAD + NADH + H + CO2CO2 Citric acid cycle CoA—SH  -Keto- glutarate CO2CO2 NAD + NADH + H + CoA—SH P Succinyl CoA i GTP GDP ADP ATP Succinate FAD FADH 2 Fumarate

48 + Fig Acetyl CoA CoA—SH Oxaloacetate Citrate H2OH2O Isocitrate NAD + NADH + H + CO2CO2  -Keto- glutarate CoA—SH NAD + NADH Succinyl CoA CoA—SH PP GDP GTP ADP ATP Succinate FAD FADH 2 Fumarate Citric acid cycle H2OH2O Malate i CO2CO2 + H + 3 4

49 + Fig Acetyl CoA CoA—SH Citrate H2OH2O Isocitrate NAD + NADH + H + CO2CO2  -Keto- glutarate CoA—SH CO2CO2 NAD + NADH + H + Succinyl CoA CoA—SH P i GTP GDP ADP ATP Succinate FAD FADH 2 Fumarate Citric acid cycle H2OH2O Malate Oxaloacetate NADH +H + NAD

50 + Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and citric acid cycle, NADH and FADH 2 account for most of energy extracted from food NADH and FADH 2 donate electrons to electron transport chain, which powers ATP synthesis via oxidative phosphorylation Electron transport chain is in cristae of mitochondrion Most of chain’s components are proteins, which exist in multiprotein complexes Carriers alternate reduced and oxidized states as they accept and donate electrons Electrons drop in free energy as they go down the chain and are finally passed to O 2, forming H 2 O

51 + Fig. 9-UN7 INTER- MEMBRANE SPACE H+H+ ATP synthase ATPADP + P i H+H+ MITO- CHONDRIAL MATRIX

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53 + Electrons transferred from NADH or FADH 2 to the electron transport chain Electrons passed through a number of proteins including cytochromes (each with an iron atom) to O 2 Electron transport chain generates no ATP ETC function: break the large free-energy drop from food to O 2 into smaller steps that release energy in manageable amounts Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

54 + Fig NADH NAD + 2 FADH 2 2 FAD Multiprotein complexes FAD FeS FMN FeS Q  Cyt b   Cyt c 1 Cyt c Cyt a Cyt a 3 IVIV Free energy (G) relative to O 2 (kcal/mol) (from NADH or FADH 2 ) 0 2 H / 2 O2O2 H2OH2O e–e– e–e– e–e–

55 + Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in ETC causes proteins to pump H + from mitochondrial matrix to intermembrane space What kind of energy is this creative? H + then moves back across membrane, passing through channels in ATP synthase ATP synthase uses exergonic flow of H + to drive phosphorylation of ATP This is example of chemiosmosis use of energy in a H + gradient to drive cellular work

56 + Fig EXPERIMENT Electromagnet RESULTS Sample Magnetic bead Internal rod Catalytic knob Nickel plate Rotation in one direction Rotation in opposite direction No rotation Sequential trials Number of photons detected (  10 3 )

57 + Fig. 9-15a EXPERIMENT Sample Magnetic bead Internal rod Catalytic knob Nickel plate Electromagnet

58 + Fig. 9-15b Rotation in one direction Rotation in opposite direction No rotation Sequential trials Number of photons detected (x 10 3 ) RESULTS

59 + Energy stored in a H + gradient across membrane couples the redox reactions of the electron transport chain to ATP synthesis Proton-motive force: H + gradient, name emphasizes its capacity to do work

60 + Let’s remember… Glycolysis  TWO pyruvic acid molecules TWO pyruvic acid  TWO acetyl CoA SO, 1 glycolysis cycle = 2 turns of Krebs Cycle 2 Krebs Cycle produces: 6 NADH 2 FADH 2 2 ATP 4 CO 2

61 + Energy Yield Glycolysis: 2 ATP Krebs Cycle: 2 ATP Each NADH molecule that supplies ETC can generate 3 ATP Each FADH 2 can generate 2 ATP 10 NADH and 2 FADH 2 made by aerobic respiration How many ATP from the NADH and FADH 2 ? During cellular respiration, most energy flows in this sequence: glucose  NADH  electron transport chain  proton-motive force  ATP About 40% of energy in a glucose molecule is transferred to ATP during cellular respiration

62 + How much energy total?! 10 NADH  30 ATP 2 FADH2  4 ATP Glycolysis  2 ATP Krebs  2 ATP TOTAL: 38 ATP

63 + In reality… Real number of ATP varies cell to cell Eukaryotic cells cannot diffuse NADH through inner mito. membrane SO! Active transport needed  Uses ATP 38-2=36

64 + Efficiency of Aerobic Respiration Almost 20x more efficient

65 + Fig Maximum per glucose: About 36 or 38 ATP + 2 ATP + about 32 or 34 ATP Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA Glycolysis Glucose 2 Pyruvate 2 NADH 6 NADH2 FADH 2 2 NADH CYTOSOL Electron shuttles span membrane or MITOCHONDRION

66 + Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Most cellular respiration requires O 2 to produce ATP Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions) In absence of O 2, glycolysis couples with fermentation or anaerobic respiration to produce ATP Anaerobic respiration uses ETC with an electron acceptor other than O 2 Ex: sulfate Fermentation uses phosphorylation instead of ETC to generate ATP

67 + Types of Fermentation Fermentation consists of glycolysis plus reactions that regenerate NAD +, which can be reused by glycolysis *CYCLE* Two common types: alcohol fermentation lactic acid fermentation

68 + Pyruvate converted to ethanol in two steps; first releasing CO 2 CO 2 released = carbonation in beer Alcohol fermentation by yeast is used in brewing, winemaking, and baking Alcoholic Fermentation

69 + Pyruvate reduced to NADH, forming lactate as an end product, with no release of CO 2 LAF in some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O 2 is scarce Cramp = LA build up when LAF overused when no O 2 available Lactic Acid Fermentation

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71 + Fermentation vs Aerobic Respiration Both: use glycolysis to oxidize glucose and other organic fuels to pyruvate Different: ATP produced per glucose molecule: Fermentation: 2 ATP Cellular Respiration: 38 ATP Anaerobes: Fermentation: Obligate anaerobes carry out it or; cannot survive in presence of O 2 Yeast and many bacteria are facultative anaerobes can survive using either fermentation or cellular respiration pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes final electron acceptors: Fermentation: an organic molecule (such as pyruvate or acetaldehyde) Cellular respiration: O 2 in cellular respiration

72 + Fig Glucose Glycolysis Pyruvate CYTOSOL No O 2 present: Fermentation O 2 present: Aerobic cellular respiration MITOCHONDRION Acetyl CoA Ethanol or lactate Citric acid cycle

73 + Evolutionary Significance of Glycolysis Glycolysis: occurs in nearly all organisms probably evolved in ancient prokaryotes before there was oxygen in atmosphere Gycolysis and citric acid cycle are major intersections to various catabolic and anabolic pathways

74 + Versatility of Catabolism Catabolic pathways funnel e- from many kinds of organic molecules into cellular respiration Glycolysis accepts wide range of carbohydrates Break it down and reuse… Proteins must be digested to amino acids  amino groups can feed glycolysis or the citric acid cycle Fats digested to glycerol  used in glycolysis; fatty acids  used in generating acetyl CoA) Fatty acids broken down by beta oxidation  yield acetyl CoA Oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate BIG PICTURE: What does this mean in terms of YOUR diet?

75 + Biosynthesis (Anabolic Pathways) Body uses small molecules to build other substances These small molecules may come directly from food, glycolysis, OR citric acid cycle

76 + Regulation of Cellular Respiration via Feedback Mechanisms Feedback inhibition is most common mechanism for control ATP concentration drops  respiration speeds up; Plenty of ATP  respiration slows down Control of catabolism based mainly on regulating activity of enzymes at strategic points in the catabolic pathway

77 + You should now be able to: 1. Explain in general terms how redox reactions are involved in energy exchanges 2. Name the three stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result 3. In general terms, explain the role of the electron transport chain in cellular respiration Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

78 + 4. Explain where and how the respiratory electron transport chain creates a proton gradient 5. Distinguish between fermentation and anaerobic respiration 6. Distinguish between obligate and facultative anaerobes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings


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