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VI. Reaction Coupling and ATP [cont.] The ATP cycle ATP Phosphorylation Strongly Endergonic Energy from exergonic reactions ADP+ P Hydrolysis Strongly Exergonic Energy for endergonic reactions VII. Metabolism Background: • • • • Metabolism of a cell = Sum of all chemical reactions in cell Chemical reactions linked in metabolic pathways Cells couple exergonic and endergonic reactions Cells regulate chemical rxns through enzymes Cells regulate enzyme activity (to regulate reactions) 1. Regulate synthesis • synthesize enzyme only when product needed 2. Regulate active state • synthesize in inactive state • activate when needed 3. Noncompetitive Inhibition (Allosteric) • molecule binds to “other” site • changes active site shape 4. Competitive inhibition • molecule binds to active site • prevents substrate binding Cells regulate enzyme activity (to regulate reactions) Feedback inhibition - Works on complex, pathway reactions - Final product “feeds back” and inhibits early enzyme in pathway I. Cellular Energy Harvest: an Overview Energy to Drive Metabolism: • • Autotrophs – use inorganic sources of energy Photoautotrophs – – • harvest sunlight convert radiant energy into chemical energy. Heterotrophs – use organic sources of energy – – live off the energy produced by autotrophs. extract energy from food catabolism Overview: Energy Harvest Overview: How is Glucose metabolized? The reaction (if glucose is used to full potential) Loss of hydrogen atoms (oxidation) C6H12O6 + 6O2 --> 6CO2 + 6H2O + ATP & Heat Gain of hydrogen atoms (reduction) Cellular respiration oxidizes food molecules! Overview: How is Glucose metabolized? Step #1 Glycolysis: In cytoplasm Glucose 2 pyruvate (Yields a little Energy) Aerobic conditions: #2 Cellular respiration: In mitochondria Lots of ATP CO2 + H2O Anaerobic conditions: #2 Anaerobic respiration or #2 Fermentation In cytoplasm To Lactate or Ethanol 2 ATP, No high energy e- Releasing Energy from Glucose ! Harvesting energy: – cells break chemical bonds – shift electrons from molecule to molecule. ! Where do the electrons go? – Aerobic respiration • final electron acceptor is Oxygen – Anaerobic respiration • final electron acceptor is not oxygen, but is an inorganic molecule (e.g. CO2, SO4) – Fermentation • final electron acceptor is an organic molecule II. Stages of Aerobic Cellular Respiration Overview Cytoplasm A. Glycolysis Glucose B. Pyruvate oxidation C. Krebs (Citric Acid) Cycle NADH Glycolysis ATP D. Electron Transport Chain Pyruvate Pyruvate oxidation NADH AcetylCoA NADH Krebs cycle Intermembrane space CO2 Mitochondrial matrix CO2 ATP FADH2 H2O ATP NAD+ and FAD eMitochondrion Electron transport chain Inner mitochondrial membrane A. Glycolysis: 1 2 6-carbon glucose (Starting material) 2 ATP P 3 P P 6-carbon sugar diphosphate P 6-carbon sugar diphosphate P P P 3-carbon sugar 3-carbon sugar phosphate phosphate 3-carbon sugar 3-carbon sugar phosphate phosphate NADH NADH 2 ATP 2 ATP 3-carbon pyruvate Priming reactionsEnergy investment. Cleavage reactions. P 3-carbon pyruvate Energy-harvesting reactions. Transferring Energy: Reduction of NAD+ Oxidation: Dehydrogenase removes electrons from substrate Reduction: Electrons in Hydrogen Transferred to NAD+ H O H Oxidation Dehydrogenase O + 2H (Enzyme) + NAD + 2H Reduction ! 2H+ + 2e Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings + NADH + H (carries 2 electrons) Substrate-Level Phosphorylation High energy phosphate bond is transferred enzymatically to ADP A. Glycolysis: Summary ! Catabolic pathway with 3 major events: 1. Priming (Energy Investment) 2. Cleavage (6-C to 2X 3-C) 3. Energy Harvesting Substrate-level phosphorylation ! Nets two ATP molecules 2 ATP used 4 ATP + 2 NADH generated Net Gain/Glucose = 2 ATP + 2 NADH ! Universal: All living organisms ! Anaerobic process (no O2 required) What do cells do with Pyruvate and NADH? Depends on whether conditions are Aerobic or Anaerobic Under Aerobic (with O2) Cellular Respiration • Use Pyruvate and NADH to generate lots more ATP… II. Stages of Aerobic Cellular Respiration Overview Cytoplasm A. Glycolysis Glucose B. Pyruvate oxidation C. Krebs (Citric Acid) Cycle NADH Glycolysis ATP D. Electron Transport Chain Pyruvate Pyruvate oxidation NADH AcetylCoA NADH Krebs cycle Intermembrane space CO2 Mitochondrial matrix CO2 ATP FADH2 H2O ATP NAD+ and FAD eMitochondrion Electron transport chain Inner mitochondrial membrane B. Pyruvate Oxidation Mitochondrion C. Kreb’s Cycles (Citric Acid Cycle) II. Stages of Aerobic Cellular Respiration Overview Cytoplasm A. Glycolysis Glucose B. Pyruvate oxidation C. Krebs (Citric Acid) Cycle NADH Glycolysis ATP D. Electron Transport Chain Pyruvate Pyruvate oxidation NADH Intermembrane space CO2 AcetylCoA NADH Krebs cycle Mitochondrial matrix CO2 ATP FADH2 H2O ATP NAD+ and FAD e- Electron transport chain Inner mitochondrial membrane Mitochondrion Electron Transport Chain: Generalized Scheme 1. NADH and FADH2 pass electrons to an electron transport chain 2. Energy is released as electrons “fall” and lose energy 3. Energy is harvested as ATP NADH ATP + NAD + 2e ! + H E Tr lect an ro Ch spo n ai rt n * Controlled release of energy for ATP synthesis! + 2e ! H H2O O2 H+ . Protein complex H+ Intermembrane space Inner mitochondrial membrane Mitochondrial matrix H+ H+ Electron carrier FADH2 NADH H+ H+ H+ H+ ATP H+ synthase FAD O 2 + H+ + NAD H H+ H + H+ H + H2O + Electron Transport Chain ADP + P H+ ATP ATP synthase OXIDATIVE PHOSPHORYLATION = One Type of Chemiosmosis O2 is the final electron acceptor in the electron transport chain; it is reduced to H20 ATP Synthase, Chemiosmosis & ATP Synthesis CHEMIOSMOSIS: The passage of high-energy electrons along the electron transport chain, which is coupled to the pumping of protons through ATP synthase, driving the production of ATP ATP Synthase II. Stages of Aerobic Cellular Respiration Overview Cytoplasm A. Glycolysis Glucose B. Pyruvate oxidation C. Krebs (Citric Acid) Cycle NADH Glycolysis ATP D. Electron Transport Chain Pyruvate Pyruvate oxidation NADH Intermembrane space CO2 AcetylCoA Mitochondrial matrix NADH CO2 Krebs cycle ATP FADH2 H2O ATP NAD+ and FAD e- Electron transport chain Inner mitochondrial membrane Mitochondrion Aerobic Respiration Efficiency Glucose 2 ATP 2 ATP Glycolysis Pyruvate Acetyl-CoA 2 NADH 4 ATP 2 NADH 6 ATP 2 ATP Krebs cycle 6 NADH 18 ATP 2 FADH2 4 ATP Total net ATP yield = 36 ATP Contrasting Energy Yields From 1 molecule of glucose: • Aerobic respiration – – – – – Glycolysis (2 ATP) Pyruvate Oxidation (none) Citric Acid cycle (2 ATP) Respiratory chain (32 ATP) ~ 36 total ATP • Fermentation – Glycolysis (2 ATP) – Fermentation (none) A. Fermentation Stage 1: Glycolysis 1 6-carbon glucose (Starting material) 2 ATP P P 6-carbon sugar diphosphate 2 3 P P 6-carbon sugar diphosphate P P 3-carbon sugar 3-carbon sugar phosphate phosphate P 3-carbon sugar 3-carbon sugar phosphate phosphate NADH NADH 2 ATP 2 ATP 3-carbon pyruvate Priming reactions. Cleavage reactions. P 3-carbon pyruvate Energy-harvesting reactions. A. Fermentation Stage 2: Recycling NADH Alcohol fermentation Glucose G L Y C O L Y S I S 2 ADP 2 ATP In cytoplasm O– C O C O CH3 Glucose In cytoplasm G L Y C O L Y S I S 2 ADP 2 ATP O– C O C O CH3 2 NAD+ 2 NADH CO2 2 Pyruvate Lactic acid fermentation H H C OH CH3 2 Ethanol H C O CH3 2 Acetaldehyde O– C O H C OH CH3 2 NAD+ 2 Lactate Yeast cells (single celled fungi) Most animal cells, lactate removed from cells by blood 2 NADH 2 Pyruvate B. Anaerobic respiration ! Archaebacteria Only Methanogens • Live in anaerobic environments (no oxygen) • Use CO2 gas as final electron acceptor; convert to methane gas (CH4) • Found in swamps, sewage treatment plants, digestive tracts of animals • Break down cellulose for herbivores (cows) • Produce marsh gas or intestinal gas (methane) Sulfur Bacteria • Live in anaerobic environments (no oxygen) • Use inorganic sulfates (SO4) as final electron acceptor; convert to hydrogen sulfide (H2S) • Found in sulfur springs Red Sulfur Bacteria Summary: Respiration without oxygen 1. Glycolysis produces a net of 2ATP 2. Fermentation - recycles NADH to NAD+ » » » Lactic acid fermentation CO2 and Ethanol fermentation NO Pyruvate Oxidation, NO Kreb’s Cycle, NO electron transport! 3. Anaerobic Respiration ! Methanogens Final electron acceptor: CO2, convert to CH4 ! Sulfate-reducing Bacteria Final electron acceptor: SO4, convert to to H2S IV. Catabolism of Macromolecules How is cellular E carried between coupled rxns? Example: Using glucose E to build a protein