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Chapter 9~ Cellular Respiration: Harvesting Chemical Energy • All energy can be traced back to the sun. • Energy flows in as sunlight and leaves as heat. Chem elements are recycled. Principles of Energy Harvest • Catabolic pathway – releases energy by oxidizing organic fuels • Energy – stored in chem bonds – released when bonds break – Used for work and given off as heat • Fermentation – partial degradation of sugars that occurs w/out O2 • Cellular Respiration – most efficient – C6H12O6 + 6O2 ---> 6CO2 + 6H2O + E (ATP + heat) Redox reactions • Oxidation/reduction – Aka redox • Oxidation is e- loss; reduction is e- gain • Reducing agent: e- donor • Oxidizing agent: e- acceptor See board Oxidizing agent in respiration • NAD+ (nicotinamide adenine dinucleotide) – coenzyme – eacceptor • Removes electrons from food (series of reactions) • NAD+ is reduced to NADH • Enzyme action: dehydrogenase – Removes a pair of H atoms from the substrate (sugar) & delivers 2e- and 1 proton (H+) to NAD+ - releases other H+ • Oxygen is the eventual eacceptor Electron transport chains • Sequence of reactions that prevents energy release in 1 explosive step • Electron carrier molecules (mitochondrial membrane proteins) • Shuttle electrons that release energy used to make ATP • Electron route: food--> NADH-->electron transport chain-->oxygen – O2 is more electronegative and pulls e- down chain Cellular respiration • Glycolysis: cytosol; degrades glucose into pyruvate • Kreb’s Cycle (Citric Acid Cycle): mitochondrial matrix; pyruvate into carbon dioxide • Electron Transport Chain (ETC): inner membrane of mitochondrion; electrons passed to oxygen Glycolysis I • • • • “splitting sugar” Occurs in cytosol w/ or w/out oxygen 1 Glucose ---> 2 pyruvate molecules • Net energy yield per glucose molecule: 2 ATP plus 2 NADH; no CO2 is released; occurs aerobically or anaerobically Glycolysis II • Energy investment phase: cell uses ATP to phosphorylate fuel – Glucose is phosphorylated by 2 ATP molecules – 2 Glyceraldehyde-3-phosphate molecules are produced • Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation • Every product is doubled because step 4 splits sugar in ½ – NADH, 2ATP, H20, and pyruvate (C3H3O3) are produced for each glyceraldehyde-3-phosphate Kreb’s Cycle I • • • • In mitochondrial matrix If molecular oxygen is present… Junction steps (1) Carboxyl group (-COO-) removed from pyruvate & released as CO2 • (2) Remaining fragment oxidized → acetate; NAD+ is reduced →NADH • (3) Coenzyme A is attached to acetate → acetyl CoA Kreb’s Cycle II • Citric Acid Cycle – Acetyl group of acetyl CoA added to oxaloacetate → Citrate – In several steps - CO2 is removed; NADH, FADH2, and ATP are produced – Oxaloacetate is regenerated (the “cycle”) – For each pyruvate that enters: • 3 NAD+ reduced to NADH • 1 FAD+ reduced to FADH2 • 1 ATP molecule • 2 CO2 – Remember: have 2 pyruvate from 1 glucose • All of the numbers will be doubled Electron transport chain • Inner membrane of mitochondria • Multiprotein Complex (I, II, III, IV) • Many of the proteins are cytochromes – have a heme group (iron) which accepts protons • NADH and FADH2 enter and release e• e- are passed down the complexes until they reach oxygen (which also picks up 2 H atoms from surrounding solution to form H2O) ATP Synthase I • Uses the energy of an existing ion gradient to power ATP synthesis (chemiosmosis – energy coupling mechanism) • Driven by difference in H+ concen on either side of inner membrane • H+ difference is created when ETC breaks down NADH and FADH2 • Synthase is the only place where H+ may flow down gradient ATP Synthase II • 4 parts: stator, rotor, rod, knob • H+ flows down btw stator and rotor • Causes rotor and rod to rotate • Rotating rod causes conformational changes to knob – Activiates catalytic sites which combine ADP and P forming ATP Review: Cellular Respiration • Glycolysis: – 2 ATP , 2 NADH, 2 Pyruvate • Kreb’s Cycle: – 2 ATP, 6 NADH, 2 FADH2, 4 CO2 • Electron transport & oxidative phosphorylation: – 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 Related metabolic processes • Fermentation: anaerobic conditions – glycolysis still occurs first – purpose to form NAD+ • Alcohol~ pyruvate to ethanol, CO2, & NAD+ • Lactic acid~ pyruvate to lactate & NAD+ • Facultative anaerobes – can do both (yeast/bacteria) • Beta-oxidation – lipid catabolism – breaks fatty acids down to 2-C fragments which entre Citric Acid Cycle – 1g fat produces more than 2X ATP as carbs