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Chapter 4

Chapter 4. Cellular Respiration. Watch the following videos!!. To get a better understanding of how cellular respiration takes place in our bodies at a cellular level please take the time to watch the following videos! http://www.youtube.com/watch?v=00jbG_cfGuQ

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Chapter 4

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  1. Chapter 4 Cellular Respiration

  2. Watch the following videos!! To get a better understanding of how cellular respiration takes place in our bodies at a cellular level please take the time to watch the following videos! http://www.youtube.com/watch?v=00jbG_cfGuQ http://www.khanacademy.org/science/biology/cellular-respiration/v/introduction-to-cellular-respiration

  3. 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

  4. Aerobic Cellular Respiration • Divided into 4 stages • Glycolysis • Pyruvate oxidation • Citric acid cycle • Electron transport 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. Glycolysis This process is for the conversion of only ONE glucose molecule!!! http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html • 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) • 2 ATP and 2 NADH • Two Phases in which this occurs • Initial energy investment phase • Energy payoff phase

  7. Glycolysis (Initial Energy Investment Phase) • Step 1 • Glucose receives a phosphate group from ATP • Produces glucose-6-phosphate • Enzyme used • hexokinase

  8. Glycolysis (Initial Energy Investment Phase) • Step 2 • Glucose-6-phosphate is rearranged into its isomer • Produces fuctose-6-phosphate • Enzyme used • Phospho-glucomutase • Recall Isomers • Same molecular formula but different structure

  9. Glycolysis (Initial Energy Investment Phase) • Step 3 • Fructose-6-phosphate receives another phosphate group from ATP • Produces fructose-1,6-bisphosphate • Enzyme Used • Phospho-fructokinase

  10. Glycolysis (Initial Energy Investment Phase) • Step 4 • Fructose-1,6-bisphosphate is split • Produces • Glyceraldehyde-3-phosphate (G3P) • Dihydroxyacetone phosphate (DHAP) • Enzyme used • aldolase

  11. Glycolysis (Initial Energy Investment Phase) • Step 5 • Dihydroxyacetone (DHAP) is converted • Produces • glyceraldehyde-3-phosphate (G3P) • Enzyme used • Triosephosphate-isomerase • This is the last step of the initial energy investment phase • Total of 2 ATP invested • End result is 2 G3P molecules

  12. IMPORTANT!!! Because there are now 2 molecules of G3P at the end of the initial energy investment phase, all the reactions in the energy payoff phase (6 to 10) are DOUBLED!!

  13. Glycolysis (Energy Payoff Phase) • Step 6 • 2 electrons and 2 protons are removed from G3P • NAD⁺ accepts both electrons and a proton (becoming NADH) • Other proton is released into cytosol • Phosphate group is attached • Produces • Two 1,3-bisphosphoglycerate • Enzyme used • Triosephosphate-dehydrogenase

  14. Glycolysis (Energy Payoff Phase) • Step 7 • A phosphate group from 1,3-bisphosphoglycerate is transferred to ADP • Produces • 2 ATP • Two 3-phosphoglycerate • Enzyme used • Phosphoglyceratekinase • ATP is produced by • Substrate-level phosphorylation

  15. Glycolysis (Energy Payoff Phase) • Step 8 • 3-phosphoglycerate is rearranged • Phosphate group is shifted from 3-carbon to 2-carbon • Produces • Two 2-phosphoglycerate • This process is done via mutase reaction • Shifting of a chemical group to another within the same molecule • Enzyme used • phosphoglucomutase

  16. Glycolysis (Energy Payoff Phase) • Step 9 • Electrons are removed from one part of 2-phosphoglycerate and delivered to another part of the molecule • Produces • Two H₂O molecules • Two Phosphoenolpyruvate • Enzyme used • Enolase

  17. Glycolysis (Energy Payoff Phase) • Step 10 • Final phosphate group is transferred from phosphoenolpyruvate (PEP) to ADP • Produces • 2 ATP • Two Pyruvate molecules • Enzyme used • Pyruvatekinase • ATP is produced by • Substrate-level phosphorylation

  18. 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

  19. Overview of Glycolysis http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_nad__works.html • 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

  20. 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

  21. Pyruvate Oxidation • Multi-step process • 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

  22. Pyruvate Oxidation Conversion of pyruvate to acetyl-CoA Involves 2 Reactions 1. Decarboxylation reaction • Carboxyl group (-COO⁻) of pyruvate is removed • Produces • CO₂ 2. 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

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

  24. Citric Acid Cycle • Discovered by • Sir Hans Krebs (1900-1981) • Consists of 8 enzyme catalyzed reaction • ALL ATP are produced by substrate-level phosphorylation • http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html

  25. Citric Acid Cycle • Step 1 • 2-carbon acetyl group carried by coenzyme A is transferred to oxaloacetate • Produces • Citrate • Enzyme used • Citrate synthase

  26. Citric Acid Cycle • Step 2 • Citrate is rearranged into its isomer • Produces • Isocitrate • Enzyme used • Aconitase

  27. Citric Acid Cycle • Step 3 • Isocitrate is oxidized • Produces • α-ketoglutarate • NADH • CO₂ • H⁺ • Enzyme used • Isocitratedehydrogenase

  28. Citric Acid Cycle • Step 4 • α-ketoglutarate is oxidized • Produces • SuccinylCoA • CO₂ • NADH • Enzyme used • α-ketoglutaratedehydrogenase

  29. Citric Acid Cycle • Step 5 • CoA is released from succinylCoA • Produces • Succinate • Energy released converts GDP to GTP which couples production of ATP • Enzyme used • SuccinylCoAsynthetase • GTP • Activates substrate to produce ATP

  30. Citric Acid Cycle • Step 6 • Succinate is oxidized • Produces • Fumarate • FADH₂ • Enzyme used • Succinatedehydrogenase • FADH₂ • Nucleotide-based molecule • Electron carrier

  31. Citric Acid Cycle • Step 7 • Fumarate is converted with the addition of H₂O • Produces • Malate • Enzyme used • Fumarase

  32. Citric Acid Cycle • Step 8 • Malate is oxidized • Produces • Oxaloacetate • NADH • H⁺ • Enzyme used • Malatedehydrogenase

  33. Overview of Citric Acid Cycle 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

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

  35. Oxidation of ONE Glucose Molecule

  36. 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 • This energy is used to synthesize additional ATP (A lot more)

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

  38. 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

  39. 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 • http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_atp_synthesis__quiz_1_.html

  40. 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!!

  41. 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

  42. 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)

  43. Proton Gradient

  44. 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

  45. 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

  46. Efficiency of Cellular Respiration

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

  48. 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

  49. Efficiency of Cellular Respiration Only 41% of the energy in glucose in converted into ATP The rest is lost as thermal energy 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

  50. 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

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