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09  cellrespiration text 09 cellrespiration text Presentation Transcript

  • Cellular Respiration: Harvesting Chemical Energy
    • Living cells
      • Require transfusions of energy from outside sources to perform their many tasks
    Figure 9.1
    • Energy
      • Flows into an ecosystem as sunlight and leaves as heat
    Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energy Figure 9.2
    • Catabolic pathways yield energy by oxidizing organic fuels (exergonic)
    • One catabolic process, fermentation
      • Is a partial degradation of sugars that occurs without oxygen
    • Cellular respiration
      • Is the most prevalent and efficient catabolic pathway
      • Consumes oxygen and organic molecules such as glucose
      • Yields ATP (Cells must regenerate ATP)
  • The Principle of Redox
    • Redox reactions
      • Transfer electrons from one reactant to another by oxidation and reduction
    • In oxidation
      • A substance loses electrons, or is oxidized
    • In reduction
      • A substance gains electrons, or is reduced
    Na + Cl Na + + Cl – becomes oxidized (loses electron) becomes reduced (gains electron)
  • Oxidation of Organic Fuel Molecules During Cellular Respiration
    • During cellular respiration
      • Glucose is oxidized and oxygen is reduced
    • Cellular respiration
      • Oxidizes glucose in a series of steps
    C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced
    • Electrons from organic compounds
      • Are usually first transferred to NAD + , a coenzyme
    Enzyme NAD + H O O O O – O O O – O O O P P CH 2 CH 2 HO OH H H HO OH HO H H N + C NH 2 H N H NH 2 N N Nicotinamide (oxidized form) NH 2 + 2[H] (from food) Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e – + 2 H + 2 e – + H + NADH O H H N C + Nicotinamide (reduced form) N Figure 9.4
    • If electron transfer is not stepwise
      • A large release of energy occurs
      • As in the reaction of hydrogen and oxygen to form water
    • NADH, the reduced form of NAD +
      • Passes the electrons to the electron transport chain
    (a) Uncontrolled reaction Free energy, G H 2 O Explosive release of heat and light energy Figure 9.5 A H 2 + 1 / 2 O 2
    • The electron transport chain
      • Passes electrons in a series of steps instead of in one explosive reaction
      • Uses the energy from the electron transfer to form ATP
  • 2 H 1 / 2 O 2 (from food via NADH) 2 H + + 2 e – 2 H + 2 e – H 2 O 1 / 2 O 2 Controlled release of energy for synthesis of ATP ATP ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B
  • The Stages of Cellular Respiration: A Preview
    • Respiration is a cumulative function of three metabolic stages
      • Glycolysis
      • The citric acid cycle (kreb’s cycle)
      • Oxidative phosphorylation (electron transport chain)
    • Glycolysis
      • Breaks down glucose into two molecules of pyruvate
    • The citric acid cycle
      • Completes the breakdown of glucose
    • Oxidative phosphorylation
      • Is driven by the electron transport chain
      • Generates ATP
    • An overview of cellular respiration
    Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol
    • Both glycolysis and the citric acid cycle
      • Can generate ATP by substrate-level phosphorylation
    Figure 9.7 Enzyme Enzyme ATP ADP Product Substrate P +
    • Glycolysis harvests energy by oxidizing glucose to pyruvate
    • Glycolysis
      • Means “splitting of sugar”
      • Breaks down glucose into pyruvate
      • Occurs in the cytoplasm of the cell
    • Glycolysis consists of two major phases
      • Energy investment phase (preparatory phase) 2 ATP used
      • Energy payoff phase – 4 ATP formed (2 ATP net)
    Glycolysis Citric acid cycle Oxidative phosphorylation ATP ATP ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD + + 4 e - + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H + Figure 9.8
  • A closer look at the energy investment phase
    • Glucose gains a phosphate from ATP and becomes glucose-6-phosphate
    • 2. glucose-6-phosphate becomes fructose-6-phosphate
    • 3. fructose-6-phosphate gains a P by phosphorylation of ATP and becomes fructose-1,6-diphosphate
    • 4. and 5. Very unstable fructose-1,6-diphosphate breaks into two molecules of G3P (glyceraldehyde-3-phosphate)
    1 ATP used – phosphorylation 1 ATP used – phosphorylation Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH OH HO HO CH 2 OH H H H H O H OH HO OH P CH 2 O P H O H HO HO H HO CH 2 OH P O CH 2 O CH 2 O P HO H HO H OH O P CH 2 C O CH 2 OH H C CHOH CH 2 O O P ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate ATP ADP Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis 1 2 3 4 5 CH 2 OH Oxidative phosphorylation Citric acid cycle Figure 9.9 A
  • A closer look at the energy payoff phase 6. G3P is oxidized, NAD+ is reduced to form NADH & the energy from this causes a P to bind to G3P changing it to 1,3-diphosphoglycerate 7. 1,3-diphosphoglycerate phosphorylates an ADP to form ATP and becomes 3-phosphoglycerate 8. 3-phosphoglycerate rearranges into 2-phosphoglycerate 9. 2-phosphoglycerate goes through a dehydration reaction and becomes PEP (phosphoenolpyruvate) 10. another substrate level phosphorylation reaction producing ATP changes PEP into pyruvate Redox reaction 2 ATP produced – phosphorylation 2 ATP produced – phosphorylation Water lost 2 NAD + NADH 2 + 2 H + Triose phosphate dehydrogenase 2 P i 2 P C CHOH O P O CH 2 O 2 O – 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase CH 2 O P 2 C CHOH 3-Phosphoglycerate Phosphoglyceromutase O – C C CH 2 OH H O P 2-Phosphoglycerate 2 H 2 O 2 O – Enolase C C O P O CH 2 Phosphoenolpyruvate 2 ADP 2 ATP Pyruvate kinase O – C C O O CH 3 2 6 8 7 9 10 Pyruvate O Figure 9.8 B
  • Glycolysis Output
    • 1 glucose and 2 ATP go in
    • 4 ATP (2 net ATP), 2 NADH (energy can only be used in presence of Oxygen), 2 H 2 O, 2H+ and 2 pyruvate come out
    Glycolysis Citric acid cycle Oxidative phosphorylation ATP ATP ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD + + 4 e - + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H + Figure 9.8
    • The citric acid cycle completes the energy-yielding oxidation of organic molecules
    • The citric acid cycle (or Kreb’s Cycle)
      • Takes place in the matrix of the mitochondrion
    • Before the citric acid cycle can begin
      • Pyruvate must first be converted to acetyl CoA, which moves from the cytoplasm into the mitochondria
      • 1. pyruvate loses 1 carbon to form CO2
      • 2. the 2C sugar is then oxidized and NAD+ is reduced to form an NADH
      • 3. coenzyme A binds to the 2C sugar to form acetyl coenzyme A (acetyl CoA)
    CYTOSOL MITOCHONDRION NADH + H + NAD + 2 3 1 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O – O O C C CH 3 Figure 9.10
    • An overview of the citric acid cycle
    ATP 2 CO 2 3 NAD + 3 NADH + 3 H + ADP + P i FAD FADH 2 Citric acid cycle CoA CoA Acetyle CoA NADH + 3 H + CoA CO 2 Pyruvate (from glycolysis, 2 molecules per glucose) ATP ATP ATP Glycolysis Citric acid cycle Oxidative phosphorylation Figure 9.11
  • Figure 9.12 1. acetyl CoA enters the cycle, CoA is removed and the remaining 2C acetyl group is bound to oxaloacetate (which is 4C), making citrate (a 6C molecule) 2. a redox reaction produces an NADH and releases one C as CO 2 changing citrate into alpha-ketoglutarate (a 5C molecule) 3. another redox reaction and substrate level phosphorylation produces an ATP, another NADH and CO 2 , changing alpha-ketoglutarate into succinate (a 4C molecule) A closer look at the citric acid cycle = intermediate molecule (short lived) Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle S CoA CoA SH NADH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CO 2 CoA SH CoA SH CoA S H 2 O + H + + H + H 2 O C CH 3 O O C COO – CH 2 COO – COO – CH 2 HO C COO – CH 2 COO – COO – COO – CH 2 HC COO – HO CH COO – CH CH 2 COO – HO COO – CH HC COO – COO – CH 2 CH 2 COO – COO – CH 2 CH 2 C O COO – CH 2 CH 2 C O COO – 1 2 3 Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12
  • A closer look at the citric acid cycle .. Cont.
    • 4. succinate is oxidized and FAD is reduced to FADH 2 , forming malate
    • 5. malate is oxidized, NAD+ is reduced to NADH, and oxaloacetate is produced (ready to start the cycle over again)
    Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle S CoA CoA SH NADH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CO 2 CoA SH CoA SH CoA S H 2 O + H + + H + H 2 O C CH 3 O O C COO – CH 2 COO – COO – CH 2 HO C COO – CH 2 COO – COO – COO – CH 2 HC COO – HO CH COO – CH CH 2 COO – HO COO – CH HC COO – COO – CH 2 CH 2 COO – COO – CH 2 CH 2 C O COO – CH 2 CH 2 C O COO – 4 5 Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12
  • Total Output Citric Acid Cycle (total = 2 pyruvate)
    • 4 CO 2 ,
    • 6 NADH,
    • 2FADH 2
    • and 2 ATP
    Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle S CoA CoA SH NADH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CO 2 CoA SH CoA SH CoA S H 2 O + H + + H + H 2 O C CH 3 O O C COO – CH 2 COO – COO – CH 2 HO C COO – CH 2 COO – COO – COO – CH 2 HC COO – HO CH COO – CH CH 2 COO – HO COO – CH HC COO – COO – CH 2 CH 2 COO – COO – CH 2 CH 2 C O COO – CH 2 CH 2 C O COO – 4 5 Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12
  • The Pathway of Electron Transport
    • In the electron transport chain
    • A series of oxidation-reduction reactions that result in phosphorylation
    • Where: in the mitochondrial inner membrane (between the intermembrane space and mitochondrial matrix)
    • Note: the cristae of the mitochondria membrane increase surface area and allow more space for this step & its mechanisms
    • 2 parts: electron transport chain & ends with chemiosmosis
    • Produces the most ATP, about 34
    • At the end of the chain
      • Electrons are passed to oxygen, forming water
  • Anatomy of a mitochondria
  • Overview
    • NADH & FADH 2 transfer electrons to the electron transport chain, a series of proteins that pass electrons along through redox reactions
    • 2. energy from the electrons is used to pump H+ out of the matrix into the intermembrane space
    • 3. oxygen is the final electron acceptor in the transport chain
    • 4. H+ diffuse back into the matrix through an ATP synthase (this is chemiosmosis)
    • 5. H+ binds to the O and forms water
    Animation: http://vcell.ndsu.nodak.edu/animations/etc/movie.htm H 2 O O 2 NADH FADH2 FMN Fe•S Fe•S Fe•S O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy ( G ) relative to O 2 (kcl/mol) Figure 9.13
  • Electron movement – Inner Membrane NADH donates 2 electrons Mitochondrial Matrix Intermembrane 2 H+ Ubiquinone Electrons passed 1 H+ at a time cytochrome c 1 electron at a time 4 H+ Four electrons must be transferred to the oxidase complex in order for the next major reaction to occur 2 H20 3 H+ to synthesize one ATP from the substrates ADP and Pi (inorganic phosphate). FADH2 donates another electron
  • Chemiosmosis: The Energy-Coupling Mechanism
    • ATP synthase
      • Is the enzyme that actually makes ATP
    ATP synthase animation: http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm INTERMEMBRANE SPACE H + H + H + H + H + H + H + H + P i + ADP ATP A rotor within the membrane spins clockwise when H + flows past it down the H + gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX Figure 9.14
    • The resulting H + gradient
      • Stores energy (potential)
      • Drives chemiosmosis in ATP synthase
      • Is referred to as a proton-motive force
    • Chemiosmosis
      • Is an energy-coupling mechanism that uses energy in the form of a H + gradient across a membrane to drive cellular work
    • Chemiosmosis and the electron transport chain
    Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP Inner Mitochondrial membrane H + H + H + H + H + ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H 2 O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15
  • An Accounting of ATP Production by Cellular Respiration – A summary!
    • There are three main processes in this metabolic enterprise
    Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH 2 2 NADH 6 NADH 2 FADH 2 2 NADH Glycolysis Glucose 2 Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16
    • About 40% of the energy in a glucose molecule
      • Is transferred to ATP during cellular respiration, making approximately 36 to 38 ATP
    With the supply of NADH exhausted, the electron transport chain can no longer maintain the proton gradient that powers ATP synthase, and ATP synthesis comes to a stop.
    • Fermentation enables some cells to produce ATP without the use of oxygen
    • Glycolysis
      • Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
      • Couples with fermentation to produce ATP
    • Both fermentation and cellular respiration
      • Use glycolysis to oxidize glucose and other organic fuels to pyruvate
  • Types of Fermentation
    • Fermentation consists of
      • Glycolysis plus reactions that regenerate NAD + , which can be reused by glyocolysis
    • In alcohol fermentation
      • Pyruvate is converted to ethanol in two steps, one of which releases CO 2
    • During lactic acid fermentation
      • Pyruvate is reduced directly to NADH to form lactate as a waste product
    2 ADP + 2 P 1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 P 1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Lactate (b) Lactic acid fermentation H H OH CH 3 C O – O C C O CH 3 H C O CH 3 O – C O C O CH 3 O C O C OH H CH 3 CO 2 2 Figure 9.17
    • Fermentation and cellular respiration
      • Differ in their final electron acceptor
    • Cellular respiration
      • Produces more ATP
    Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18
    • Glycolysis and the citric acid cycle connect to many other metabolic pathways
    Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH 3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19
  • Biosynthesis (Anabolic Pathways)
    • The body
      • Uses small molecules to build other substances (at the cost of ATP molecules)
    • These small molecules
      • May come directly from food or through glycolysis or the citric acid cycle
  • Regulation of Cellular Respiration via Feedback Mechanisms
    • Cellular respiration
      • Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle
    Example: excess ATP production serves to inhibit phosphofructokinase in glycolysis, AMP stimulates its production
    • AMP can be produced during ATP synthesis by the enzyme adenylate kinase by combining two ADP molecules:
      • 2 ADP -> ATP + AMP
    Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + – – Figure 9.20
  • Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH OH HO HO CH 2 OH H H H H O H OH HO OH P CH 2 O P H O H HO HO H HO CH 2 OH P O CH 2 O CH 2 O P HO H HO H OH O P CH 2 C O CH 2 OH H C CHOH CH 2 O O P ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate ATP ADP Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis 1 2 3 4 5 CH 2 OH Oxidative phosphorylation Citric acid cycle Figure 9.9 A 2 NAD + NADH 2 + 2 H + Triose phosphate dehydrogenase 2 P i 2 P C CHOH O P O CH 2 O 2 O – 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase CH 2 O P 2 C CHOH 3-Phosphoglycerate Phosphoglyceromutase O – C C CH 2 OH H O P 2-Phosphoglycerate 2 H 2 O 2 O – Enolase C C O P O CH 2 Phosphoenolpyruvate 2 ADP 2 ATP Pyruvate kinase O – C C O O CH 3 2 6 8 7 9 10 Pyruvate O Figure 9.8 B
  • CYTOSOL MITOCHONDRION NADH + H + NAD + 2 3 1 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O – O O C C CH 3 Figure 9.10
  • Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle S CoA CoA SH NADH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CO 2 CoA SH CoA SH CoA S H 2 O + H + + H + H 2 O C CH 3 O O C COO – CH 2 COO – COO – CH 2 HO C COO – CH 2 COO – COO – COO – CH 2 HC COO – HO CH COO – CH CH 2 COO – HO COO – CH HC COO – COO – CH 2 CH 2 COO – COO – CH 2 CH 2 C O COO – CH 2 CH 2 C O COO – 4 5 Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12
  • Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP Inner Mitochondrial membrane H + H + H + H + H + ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H 2 O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15