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Aerobic Cellular Respiration

Aerobic Cellular Respiration. Process that extracts energy from food (mainly glucose, but also proteins and lipids) in the presence of oxygen – obligate aerobes The energy that is extracted is used to synthesize ATP ATP is used to supply energy directly to cells to drive chemical reactions.

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Aerobic Cellular Respiration

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  1. Aerobic Cellular Respiration • Process that extracts energy from food (mainly glucose, but also proteins and lipids) in the presence of oxygen –obligate aerobes • The energy that is extracted is used to synthesize ATP • ATP is used to supply energy directly to cells to drive chemical reactions

  2. Why Make ATP? • Referred to as energy currency of the cell • Provide energy for chemical reactions to take place in our body (cells)

  3. Mitochondria • Site of cellular respiration (where ATP is made) • Conists of • Outer membrane • Inner membrane • Matrix • Cristae

  4. Aerobic Cellular Respiration • Divided into 4 stages • Glycolysis • Pyruvate oxidation • Citric acid cycle • Electron transport chain and oxidative phosphorylation • Each Stage involves the transfer of FREE ENERGY • ATP is produced in two different ways • Substrate-level phosphorylation • Oxidative phosphorylation

  5. Aerobic Respiration • Location of each Stage • Glycolysis • Cytosol • Pyruvate Oxidation • Mitochondrion • Citric Acid Cycle • Mitochondrion • Electron Transport • Mitochondrion

  6. This process is for the conversion of only ONE glucose molecule!!! Glycolysis • Primitive • Process found in almost all organisms • Both prokaryotes and eukaryotes • Does not require O₂ • Involves • Soluble enzymes (10 sequential enzyme-catalyzed reactions) • Oxidation of a 6-carbon sugar glucose • Produces • 2 molecules of pyruvate (3-carbon molecule) • 4 ATP and 2 NADH • Two Phases in which this occurs • Initial energy investment phase • Energy payoff phase

  7. Glycolysis Overview

  8. Glycolysis Overview • Initial energy investment phase • 2 ATP are consumed • Energy payoff phase • 4 ATP produced • 2 NADH molecules are synthesized Overall NET reaction; Glucose + 2 ADP + 2 Pi + 2 NAD⁺ → 2 pyruvate + 2 ATP + 2 NADH + 2H⁺ • 62 kJ of energy is stored by the synthesis of 2 ATP molecules • Rest of the free energy is stored in the 2 pyruvate molecules

  9. Substrate-Level Phosphorylation • Phosphate groups are attached to ADP from a substrate forming ATP (enzyme catalyzed reaction) • ALL ATP molecules are produced this way in Glycolysis

  10. Pyruvate • Pyruvate can take 2 paths from this point: • Aerobic Respiration (with oxygen) • Pyruvate moves into mitochondria and ATP is made via Krebs Cycle and Electron Transport Chain • Anaerobic Respiration (without oxygen) • Pyruvate stays in cytoplasm and is converted into lactic acid -Lactic Acid Fermentation

  11. PyruvateOxididation • Remember glycolysis occurs in the cytosol of the cell • The Citric Acid Cycle (next step) occurs in the mitochondrial matrix • Pyruvate must pass through the inner and outer membrane of the mitochondrion

  12. Pyruvate Oxidation • Outer membrane • Pyruvate diffuses across the outer membrane through large pores of mitochondrion • Inner membrane • Pyruvate-specific membrane carrier is required • Inside Matrix • Pyruvate is converted into an acetyl group • Acetyl group is bonded to coenzyme A • Produces an acetyl-CoA complex

  13. Pyruvate Oxidation Conversion of pyruvate to acetyl-CoA Involves 2 Reactions • Decarboxylation reaction • Carboxyl group (-COO⁻) of pyruvate is removed • Produces • CO₂ • Dehydrogenation reaction • 2 electrons and a proton are transferred • Produces • NADH • H⁺ in solution Net reaction 2 pyruvate + 2 NAD⁺ + 2 CoA → 2 acetyl-CoA + 2 NADH + 2 H⁺ + 2 CO₂

  14. Pyruvate Oxidation • Acetyl group reacts with the sulfur atom of coenzyme A • Acetyl-CoA is the molecule that will start the Citric Acid Cycle

  15. Citric Acid Cycle • Discovered by • Sir Hans Krebs (1900-1981) • Consists of 8 enzyme catalyzed reaction • ALL ATP are produced by substrate-level phosphorylation

  16. Citric Acid Cycle Overview • 2 molecules of pyruvate are converted to Acetyl-CoA • Citric Acid Cycle goes through two turns for every single glucose molecule that is oxidized 1 Turn • Acetyl-CoA + 3 NAD⁺ + FAD + ADP + Pi → 2 CO₂ + 3 NADH + 3 H⁺ + FADH₂ + ATP + CoA • ATP is synthesized by substrate level phosphorylation coupled by GTP

  17. Citric Acid Cycle Overview

  18. Citric Acid Cycle • ALL of the carbon atoms that make up a glucose molecule are converted into CO₂ • oxidation of pyruvate • acetyl groups 6CO₂

  19. Oxidation of ONE Glucose Molecule

  20. Electron Transport Chain (Chemiosmosis) • Process that extracts potential energy that is stored in NADH and FADH₂ • These molecules were formed during glycolysis, pyruvate oxidation, and citric acid cycle • Redox reactions – transfer of electrons • This energy is used to synthesize additional ATP (A lot more) via oxidative phosphorylation

  21. The Electron Transport Chain • Occurs on the inner mitochondrial membrane • Facilitates the transfer of electrons from NADH and FADH₂ to O₂

  22. The Electron Transport Chain • Composed of • 4 Complexes • Complex I, NADH dehydrogenase • Complex II, succinatedehydrogenase • Complex III, cytochrome complex • Complex IV, cytochromeoxidase • 2 Electron shuttles • Ubiquinone (UQ) • Hydrophobic molecule – shuttles electrons from complex I and II to complex III • Cytochrome C (cyt c) • Shuttles electrons from complex III to complex IV

  23. The Driving Force Behind Electron Transport • Complexes I, III, IV • Each has a cofactor • Each cofactor has increasing electronegativity • Alternate between reduced and oxidized states • Electrons move towards more electronegative molecules (downstream) • Final electron acceptor – OXYGEN (most electronegative) • Pulls electrons from complex IV

  24. How a Single Oxygen Atom Works (O) • Final electron acceptor • Removes two electrons from complex IV • Reacts with 2 H⁺ to produce H₂O • BUT WE BREATH IN O₂ NOT A SINGLE O • So for every O₂ molecule • Pulls a total of 4 electrons through the electron transport chain • 2 H₂O molecules are produced • Pulling 4 electrons from complex IV triggers a chain reaction between other complexes!!

  25. What happens in this chain of reactions? • Starts with O₂ • Pulls electrons through the chain of complexes • NADH is least electronegative but contains most free energy • O₂ has highest electronegativity but contains least amount of free energy

  26. Proton Gradient • Electron Transport from NADH or FADH₂ to O₂ does not produce any ATP!! • What does? • Proton Gradient • Transport of H⁺ ions across the inner mitochondrial membrane from the matrix into the inter-membrane space • Creates • Proton-Motive Force • Chemical gradient (difference in concentrations) • Electro potential gradient is created (because of the positive charge on Hydrogen atom)

  27. Proton Gradient

  28. Chemiosmosis • The ability of cells to use the proton-motive force to do work • Synthesizes ATP using electrochemical gradient • Uses ATP synthase enzyme • ATP is synthesized using oxidative phosphorylation

  29. Oxidative Phosphorylation • Relies on ATP synthase • Forms a channel which H⁺ ions can pass freely • H⁺ ions cause the synthase to rotate harnessing potential energy to synthesize ATP

  30. Efficiency of Cellular Respiration

  31. NADH and FADH₂ • NADH produced during glycolysis is in cytosol • Transported into mitochondria via two shuttle systems • Malate-aspartate shuttle • Glycerol-phosphate shuttle

  32. NADH and FADH₂ • For every NADH that is oxidized • About 3 ATP are synthesized • 10 NADH x 3 ATP = 30 ATP • For every FADH₂ • About 2 ATP are synthesized • 2 FADH₂ x 2 ATP = 4 ATP • Total of 34 ATP synthesized by electron transport chain

  33. Efficiency of Cellular Respiration • 38 ATP produced • Hydrolysis of ATP yields 31kJ/mol • 31 kJ/mol x 38 ATP = 1178 kJ/mol • Glucose contains 2870 kJ/mol of energy Only 41% of the energy in glucose in converted into ATP The rest is lost as thermal energy

  34. Cells that need a constant supply of ATP • Brain cells, muscle cells • Need burst of ATP during periods of activity • Creatine phosphate pathway • Creatine is phosphorylated • High energy molecule • Stored within cell • Used to generate additional ATP when needed creatine + ATP → creatine phosphate + ADP creatine phosphate → creatine + ATP

  35. Cellular Respiration • Regulated • Feedback inhibition • Enzyme used • Phosphofructokinase • Inhibited by • High levels of ATP • High levels of citrate • Activated by • High levels of ADP • High levels of AMP • Glucose • Stored as glycogen

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