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2.2 Cellular Respiration: The Details

2.2 Cellular Respiration: The Details. Goals; Break the bonds b/w the 6 C atoms of glucose, resulting in 6 CO 2 molecules Move H atom electrons from glucose to oxygen, forming 6 water molecules Trap as much of the free energy released in the process as possible in the form of ATP. .

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2.2 Cellular Respiration: The Details

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  1. 2.2 Cellular Respiration: The Details • Goals; • Break the bonds b/w the 6 C atoms of glucose, resulting in 6 CO2 molecules • Move H atom electrons from glucose to oxygen, forming 6 water molecules • Trap as much of the free energy released in the process as possible in the form of ATP

  2. C6H12O6 + 6O2 ATP + 6H2O + 6CO2 Overview of cellular respiration • 4 metabolic stages • Anaerobic respiration 1. Glycolysis (substrate level phosphorylation) • respiration without O2 • in cytosol • Aerobic respiration • respiration using O2 • in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain and chemiosmosis (oxidative phosphorylation) (+ heat)

  3. Energy Transfer • How is the chemical potential energy in glucose transformed into ATP? • Substrate-Level Phosphorylation • Oxidative Phosphorylation

  4. Substrate-Level Phosphorylation • A molecule containing a phosphate transfers it to ADP (with the aid of enzymes), forming ATP. 31kJ/mol of free energy is also transferred. • For each glucose molecule, 4 ATP are made this way in glycolysis (stage 1) and 2 ATP in the Kreb’s cycle (stage 3)

  5. Oxidative Phosphorylation • ATP is formed indirectly through a series of enzyme-catalyzed redox reactions involving oxygen as the final electron acceptor • It begins when the compound NAD+ (nicotinamide adenine dinucleotide), which is a coenzyme, removes 2 H atoms (2 protons and 2 electrons) from glucose. • 2 electrons and 1 proton attach and reduce NAD+ to NADH, while the left over proton dissolves in surrounding solution H+(aq)

  6. Oxidative Phosphorylation • NADH is formed during glycolysis, pyruvate oxidation and 3 times in the Kreb’s cycle • A dehydrogenase enzyme catalyzes this rxn. • FAD (flavin adenine dinucleotide) also acts like NAD+ and is reduced by 2 H atoms from glucose to form FADH2 (occurs in Kreb’s cycle) • These reductions are both energy harvesting rxns that will later transfer most of their free energy to ATP

  7. Oxidative Phosphorylation • These co-enzymes (reduced FADH2 and NADH) function as energy carriers • So, how does the free energy get transferred to ATP? It occurs in Stage 4 (electron transport and chemiosmosis) and requires oxygen…discussed later!

  8. Aerobic respiration happens in 4 stages: Stage 1 – Glycolysis (10 step process occurring in cytoplasm) glycolysis glucose splitting

  9. Stage 2-Pyruvate oxidation-1 step process occurring in the mitochondrial matrix • Stage 3-Kreb’s Cycle (citric acid cycle) 8 step cyclical process occurring in the mitochondrial matrix • Stage 4 Electron Transport and chemiosmosis (oxidative phosphorylation) multi step process occurring in the inner mitochondrial membrane (cristae)

  10. outer membrane intermembrane space inner membrane cristae matrix mitochondrialDNA Mitochondria — Structure • Double membrane energy harvesting organelle • smooth outer membrane • highly folded inner membrane • cristae • intermembrane space • fluid-filled space between membranes • matrix • inner fluid-filled space • DNA, ribosomes • enzymes • free in matrix & membrane-bound What cells would have a lot of mitochondria?

  11. In glycolysis, a glucose molecule (6 carbon) is broken down into two 3-carbon pyruvate (pyruvic acid) molecules. glucose series of enzyme controlled reactions energy released to make small quantity of ATP (2 molecules) pyruvic acid Glycolysis does not require oxygen

  12. -ate or acid??? • -ate replaces the word acid in organic acids to indicate the ionized form of the acid • E.g. pyruvic acid-pyruvate • E.g. aspartic acid-aspartate

  13. Fig 11 (p.98) • The overall chemical equation for glycolysis glucose + 2ADP + 2Pi + 2NAD+ 2 pyruvate + 2ATP + 2(NADH + H+) • The energy yield for glycolysis 4 ATP produced 2 ATP used 2 ATP produced net (can be used immediately) 2 NADH produced (used later to obtain more ATP)

  14. Glycolysis • Alone, this process is not efficient in transferring energy from glucose (only 2.2%) • Some is lost as heat but most of the energy is trapped in the pyruvate and NADH • Glycolysis is thought to be the earliest form of energy metabolism. • Video -http://www.youtube.com/watch?v=x-stLxqPt6E • Song-http://www.youtube.com/watch?v=6JGXayUyNVw

  15. Your turn… • Read p.94-100 and note sheets • Answer Q 1-10 on p.115 • Fill out glycolytic Pathway • Quiz on Wednesday, October 13th (all 10 steps with enzymes)

  16. Stage 2 – Pyruvate oxidation • The pyruvic acid made in glycolysis (stage1) still contains a lot of energy and are transported through the mitochondrial membranes into the matrix • A multi-enzyme complex catalyzes 3 changes

  17. Pyruvate oxidation • A carboxyl group is removed as CO2 (a decarboxylation rxn using the enzyme pyruvate decarboxylase) • NAD+ is reduced by 2 H atoms (food) to form NADH. The NAD+ oxidizes the 2-C portion and becomes acetic acid. This is a redox rxn as pyruvate is oxidized and NAD+ is reduced • Coenzyme A (contains S) is attached to the remaining acetic acid portion to form acetyl-CoA in an unstable bond (sets it up for stage 3)

  18. Pyruvate oxidation equation 2 pyruvate + 2 NAD+ + 2 CoA 2 acetyl-CoA + 2 NADH + 2 H+ + 2 CO2 Where do the products go? • Acetyl-CoA move to stage 3-Krebs Cycle • NADH move to stage 4-Electron Transport/Chemiosmosis (produce ATP by oxidative phosphorylation) • CO2 exits as waste • H+ remain dissolved in the matrix

  19. It is multifunctional; If the body needs energy it moves into the Kreb’s cycle, if not it produces lipids (energy storing) Many nutrients catabolized for energy are converted to acetyl-CoA and then channeled toward fat or ATP production-depending on energy needs. What exactly is Acetyl CoA?

  20. Anaerobic Respiration(in animals) anaerobic = in the absence of oxygen

  21. In low oxygen conditions or during heavy exercise, when not enough oxygen can be supplied, muscle cells swap to anaerobicrespiration

  22. glucose glycolysis still happens as it does not require oxygen 2 ADP + 2 Pi 2 ATP pyruvic acid in absence of oxygen pyruvic acid is turned into lactic acid. lactic acid

  23. A build up of lactic acid produces musclefatigue. Muscle fatigue makes muscles ache and contract less powerfully.A recovery period is needed. During this time more oxygen is taken in to convert the lactic acid back into pyruvic acid again.The volume of oxygen needed is called the oxygendebt.

  24. Summary glucose pyruvic acid oxygen debt e.g. during hard exercise oxygen debt repaid during recovery time lactic acid

  25. Anaerobic Respiration in plants The same process occurs in plants and yeast in low oxygen conditions, e.g. muddy, flooded soils.

  26. glucose pyruvic acid 2 ADP + 2 Pi 2 ATP glycolysis still happens, producing 2 ATP molecules This time in absence of oxygen, pyruvic acid is turned into carbon dioxide and ethanol This is irreversible ethanol + carbon dioxide

  27. Comparison of aerobic and anaerobic respiration

  28. pyruvate  ethanol + CO2 3C 2C 1C pyruvate  lactic acid NADH NADH NAD+ NAD+ 3C 3C Fermentation (anaerobic) • Bacteria, yeast back to glycolysis • beer, wine, bread • Animals, some fungi back to glycolysis • cheese, anaerobic exercise (no O2)

  29. pyruvate  ethanol + CO2 3C 2C 1C NADH NAD+ recycleNADH Alcohol Fermentation bacteria yeast back to glycolysis • Dead end process • at ~12% ethanol, kills yeast • can’t reverse the reaction

  30. O2 pyruvate  lactic acid NADH NAD+ 3C 3C recycleNADH Lactic Acid Fermentation animalssome fungi  back to glycolysis • Reversible process • once O2 is available, lactate is converted back to pyruvate by the liver

  31. O2 O2 Pyruvate is a branching point Pyruvate fermentation anaerobicrespiration mitochondria Krebs cycle aerobic respiration

  32. Stage 3: Kreb’s Cycle • 8-step process catalyzed by enzymes • Considered cyclic b/c oxaloacetate (the product of step 8) is the reactant in step 1 • Cycles through twice for every glucose molecule as there are 2 molecules of acetyl CoA. • Equation; Oxaloacetate + acetyl-CoA +ADP +Pi +3 NAD+ + FAD CoA + ATP + 3 NADH + 3H+ + FADH2 + 2 CO2 + oxaloacetate

  33. The Krebs Cycle • Occurs in the matrix of the mitochondrion. Transfers energy from organic molecules to ATP, NADH, FADH2 and removes C atoms as CO2 • Aerobic phase (requires oxygen). By the end of the Kreb’s Cylce the original glucose molecule is entirely consumed Steps • 2-carbon acetyl CoA joins with a 4-carbon compound (oxaloacetate) to form a 6- carbon compound called Citrate. CoA is released (recycled)

  34. The Krebs Cycle Steps • Citrate (6-C) is re-arranged to isocitrate (6-C) • Isocitrate is converted to alpha-ketoglutarate (5-C) by losing a CO2 and 2 H atoms that reduce NAD+ to NADH

  35. The Krebs Cycle Steps 4. Alpha-ketoglutarate (5-C) is converted into succinyl CoA (4-C). One CO2 is removed, coenzyme A is added and 2 H atoms reduce NAD+ to NADH. 5. Succinyl CoA (4-C) is converted to succinate (4-C). ATP is formed by substrate level phosphorylation and coenzyme A is released

  36. The Krebs Cycle Steps 6. Succinate (4-C) is converted to fumarate (4-C). Two H reduce FAD to FADH2 7. Fumarate (4-C) is converted to malate (4-C). This is a hydrolysis rxn 8. Malate (4-C) is converted to oxaloacetate (4-C). Two H reduce NAD+ to NADH

  37. Highlights • Video-http://www.youtube.com/watch?v=XVWdeKoiEOc • Energy is harvested in steps 3 (NADH), 4 (NADH) , 5 (ATP-substrate-level phosphorylation), 6 (FADH2), 8 (NADH) • The last 4 C atoms of the original glucose leave as CO2 (waste)

  38. Grand Total so far… • Glycolysis (2 ATP, 2 NADH) • Pyruvate oxidation (2 NADH, 2 CO2) • Kreb’s Cycle (after 2 cycles) • 6 NADH • 2 FADH2 • 2 ATP • 4 CO2 • The 12 reduced coenzymes (energy carriers) will eventually be transferred to ATP in stage 4

  39. Where did all the carbons go? • 6-C (glucose) at the end of glycolysis is transformed into two 3-C pyruvate • After pyruvate oxidation you are left with two CO2 and two acetyl CoA (2 carbons each) • Once the Kreb’s Cycle is completed you lose the last four original carbons as CO2

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