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Cellular Respiration Harvesting Chemical Energy
The process of converting organic “sugar” (potential) energy into a more usable form ATP.
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Principles of Energy Harvest
Catabolic pathway C6H12O6 + 6O2 ---> 6CO2 + 6H2O + E (ATP + heat) 2 pathways: Fermentation (Anaerobic) Without O2 Less efficient at producing ATP. By products: alcohol, or lactic acid Cellular Respiration (Aerobic) With O2 Most prevalent and efficient process for producing ATP
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Where in the world is …..??? Mitochondria of eukaryotes.
Cytoplasm of prokaryotes.
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Negative Feedback When ATP concentration down, respiration speeds up.
When ATP concentration up, respiration slows down.
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Redox reactions Oxidation-reduction LEO GER
OIL RIG (adding e- reduces + charge) Oxidation is e- loss Reduction is e- gain Reducing agent: e- donor Oxidizing agent: e- acceptor
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Oxidizing agent in respiration
NAD+ (nicotinamide adenine dinucleotide) Removes electrons from food NAD+ is reduced to NADH Enzyme action: dehydrogenase Oxygen is the eventual e- acceptor
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Electron transport chains
Electron carrier molecules (membrane proteins) Electron route: Food NADH ETC O2 Chemiosmosis: energy coupling mechanism Shuttles electrons that release energy creating a proton gradient used to make ATP
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Cellular respiration Glycolysis: degrades glucose into pyruvate
In cytosol Kreb’s Cycle: pyruvate into carbon dioxide In mitochondrial matrix Electron Transport Chain: electrons passed to oxygen In inner membrane of mitochondrion
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Glycolysis 1 Glucose ---> 2 pyruvate molecules
Energy investment phase: cell uses ATP as fuel Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation Net energy yield per glucose molecule: 2 ATP plus 2 NADH no CO2 is released occurs aerobically or anaerobically
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The Transition Reaction
In the presence of oxygen, the two pyruvate molecules produced by glycolysis travel to mitochondria Pyruvate is converted into acetyl CoA by removing CO2. NAD+ is converted into NADH. Coenzyme A (from B vitamin), attaches to the remaining 2-C (acetyl) unit, forming acetyl Co-A.
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Kreb’s Cycle (citric acid cycle)
Occurs in mitochondrial matrix Krebs Cycle has 8 steps, each step is catalyzed by a different enzyme Each cycling requires the input of 2-carbon acetyl-CoA and two carbons are released as C02 4-C Oxaloacetate is regenerated (the “cycle”) For each pyruvate that enters: 3 NAD+ reduced to NADH 1 FAD+ reduced to FADH2 1 ATP molecule Each are used in the electron transport system to create large amounts of ATP
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Electron transport chain
Electron transport chain Cytochromes carry e-’s from carrier molecules (NADH & FADH2) down to oxygen Produces H+ gradient pumped into the inner membrane space from E of passing e-’s ATP synthase: Enzyme harnesses E from the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)
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NET RESULTS: Aerobic Respiration
Glycolysis: 2 ATP Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) Electron transport & oxidative phosphorylation: 1 NADH = 3ATP 1 FADH2 = 2ATP Totals: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose 2 ATP used to move NADH to the mitochondria grand total of 36 ATP/glucose
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Related metabolic processes
Fermentation: Anaerobic conditions (O2 Absent) Occurs solely in cytoplasm alcohol~ pyruvate to ethanol (yeast) lactic acid~ pyruvate to lactate (humans) Facultative anaerobes Can carry out metabolism in the presence or absence of O2 (Humans) Beta-oxidation lipid catabolism
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