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AP Biology Ms. Gaynor

AP Biology Ms. Gaynor. Chapter 9 (Part 1): Cellular Respiration. Light energy. ECOSYSTEM. Photosynthesis in chloroplasts. Organic molecules. CO 2 + H 2 O. + O 2. Cellular respiration in mitochondria. ATP. powers most cellular work. Heat energy.

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AP Biology Ms. Gaynor

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  1. AP BiologyMs. Gaynor Chapter 9 (Part 1): Cellular Respiration

  2. Light energy ECOSYSTEM Photosynthesisin chloroplasts Organicmolecules CO2 + H2O + O2 Cellular respirationin mitochondria ATP powers most cellular work Heatenergy Energy Flows into ecosystems as sunlight and leaves as heat http://wps.aw.com/bc_campbell_biology_7/

  3. Carbon Cycle

  4. Reminder…. • Anabolic pathways (“A” for add together) • Build molecules from simpler ones (ex: photosynthesis) • Consume energy (endergonic) • Catabolic pathways (“C” for cut in parts) • Break down complex molecules into simpler compounds (ex: cell respiration) • Release energy (exergonic)

  5. Cellular respiration • Most efficient catabolic pathway • Consumes O2 and organic molecules (ex: glucose) • Yields ATP To keep working cells must regenerate ATP

  6. Catabolic pathways yield energy by oxidizing organic fuels • The breakdown of organic molecules is exergonic • One catabolic process, fermentation • Is a partial degradation of sugars that occurs without oxygen • Another example is cellular respiration

  7. Cellular respiration • Occurs in mitochondria • similar to combustion of gas in an engine after O2 is mixed with hydrocarbon fuel. • Food = fuel for respiration. • The exhaust =CO2 and H2O. The overall process is: organic compounds + O2  CO2 + H2O + energy (ATP + heat) • Carbohydrates, fats, and proteins can all be used as the fuel, but most useful is glucose.

  8. Mitochondria • # of mito’s in a cell varies by organism & tissue type • has its own independent DNA (and ribosomes)  this DNA shows similarity to bacterial DNA • according to the endosymbiotic theory mitochondria (and chloroplasts) are descended from free-living prokaryotes.

  9. Mitochondrion Structure

  10. Mitochondrion Structure • Outer membrane – similar to plasma membrane; contains integral proteins • Inner membrane- NOT permeable to ions (needs help to cross); there is a membrane potential across the inner membrane; contains ATP synthase • Cristae – large surface area due to folding • Matrix- gel-like in middle or lumen; many contains enzymes for cellular respiration

  11. RECALL…Redox Reactions • Catabolic pathways yield energy • Due to the transfer of electrons • Redox reactions • Transfer e-’s from one reactant to another by oxidation and reduction • In oxidation • Substance loses e-s (it’s oxidized) • In reduction • Substance receives e-s (it’s reduced)

  12. becomes oxidized(loses electron) Na + Cl Na+ + Cl– becomes reduced(gains electron) Examples of redox reactions Xe- + Y  X + Ye- **energy must be added to remove e- X = e- donor = reducing agentand reduces Y. Y = e- recipient = oxidizing agentand oxidizes X.

  13. becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced Oxidation of Organic Fuel Molecules During Cellular Respiration • During cellular respiration • Glucose is oxidized • oxygenis reduced • E-’s lose potential energy  energy is released http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/ets_flash.html

  14. 2 e– + 2 H+ 2 e– + H+ NAD+ NADH H Dehydrogenase O O H H Reduction of NAD+ + + 2[H] C NH2 NH2 C (from food) Oxidation of NADH N N+ Nicotinamide(reduced form) Nicotinamide(oxidized form) CH2 O O O O– P O H H OH O O– HO P NH2 HO CH2 O N N H N H N O H H HO OH Figure 9.4 Electrons are not transferred directly to oxygen but are passed first to a coenzyme called NAD+ or FAD NAD+ and FAD= e- acceptor and oxidating agent

  15. 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis ofATP 2 H+ + 2 e– ATP ATP Free energy, G Electron transport chain ATP 2 e– 1/2 O2 2 H+ H2O Electron Flow = (b) Cellular respiration food  NADH/FADH2 ETC  oxygen

  16. The Stages of Cellular Respiration • Respiration is a cumulative process of 3 metabolic stages 1. Glycolysis 2. The citric acid cycle 3. Oxidative phosphorylation

  17. The 3 Stages • Glycolysis • Breaks down glucose into 2 molecules of pyruvate • Makes NADH • Kreb’s Cycle (Citric acid cycle) • Completes the breakdown of glucose • Makes NADH and FADH2 • Oxidative phosphorylation • Driven by the electron transport chain • Generates ATP

  18. Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidativephosphorylation:electron transport andchemiosmosis Citric acid cycle Glycolsis 2 Pyruvate Glucose Cytoplasm Mitochondrion Matrix ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation Figure 9.6 • An overview of cellular respiration Inner Mitochondrion Membrane (Cristae)

  19. Enzyme Enzyme ADP P Substrate + ATP Product Figure 9.7 • Both glycolysis and the citric acid cycle • Can generate ATP by substrate-level phosphorylation (not using ATP synthase!)

  20. Stage #1: Glycolysis • Glycolysis produces energy by oxidizing glucose  pyruvate • Glycolysis • Means “splitting of sugar” • Breaks down glucose into pyruvate • Occurs in the cytoplasmof the cell 1 glucose breaks down  4 ATP made + 2 pyruvate molecules (net gain of 2 ATP…NOT 4 ATP)

  21. Glycolysis Oxidativephosphorylation Citricacidcycle ATP ATP ATP Energy investment phase 1 Glucose 2 ADP + 2 used P 2 ATP Energy payoff phase formed 4 ATP 4 ADP + 4 P 2 NAD+ + 4 e- + 4 H + 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NADH 2 NAD+ + 4 e– + 4 H + • Glycolysis consists of two major phases 1. Energy investment phase (endergonic= uses 2 ATP) 2. Energy payoff phase (exogonic = makes 4 ATP)

  22. Glycolysis NET • Glucose  2 pyruvate (pyruvic acid) + 2 H2O • 4 ATP formed – 2 ATP used  2 ATP GAIN • substrate-level phosphorylation used • 2 NAD+ + 4e- + 4H+  2 NADH + 2H+ **Glycolysis can proceed WITHOUT O2

  23. The energy investment & Payoff phases of Glycolysis • Let’s take a closer look…. • Page 166-167 in textbook • 10 steps in glycolysis occuring in 2 phases

  24. CH2OH Citric acid cycle H H Oxidative phosphorylation H Glycolysis H HO HO OH H OH Glucose 1 2 3 5 4 ATP Hexokinase ADP CH2OH P O H H H H OH HO H OH Glucose-6-phosphate Phosphoglucoisomerase CH2O P O CH2OH H HO HO H H HO Fructose-6-phosphate ATP Phosphofructokinase ADP CH2 O O CH2 P P O HO H OH H HO Fructose- 1, 6-bisphosphate Aldolase H O CH2 P Isomerase C O O C CHOH CH2OH O CH2 P Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Figure 9.9 A Phase #1: The Investment Phase of Glycolysis(endergonic)

  25. Phase #2: The Payoff Phase of Glycolysis (exogonic) 2 NAD+ Triose phosphate dehydrogenase P i 2 2 NADH + 2 H+ 10 7 9 6 8 2 O C O P CHOH P CH2 O 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase (PFK) 2 ATP O– 2 C CHOH O P CH2 3-Phosphoglycerate Phosphoglyceromutase O– 2 C O C P H O CH2OH 2-Phosphoglycerate Enolase 2 H2O O– 2 C O P C O CH2 Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP O– 2 C O C O CH3 Figure 9.8 B Pyruvate • Phosphofructoskinase (PFK) • is an allosteric enzyme • ATP acts as an allosteric inhibitor to PFK • High [ATP]  stops glycolysis via inhibition (blocks active site)

  26. Glycolysis • http://www.northland.cc.mn.us/biology/Biology1111/animations/glycolysis.html • http://www.hippocampus.org/AP%20Biology%20II • Watch Glycolysis

  27. Stage #2: The Kreb’s Cycle • The citric acid cycle • Takes place in the matrix of the mitochondrion **NEEDS O2 TO PROCEED (unlike glycolysis)

  28. CYTOSOL MITOCHONDRION NAD+ + H+ NADH O– CoA S 2 C O C O C O CH3 1 3 Acetyle CoA CH3 Coenzyme A (a vitamin) CO2 Pyruvate Transport protein Figure 9.10 • Stage #1 ½ : The Citric Acid Cycle • Before the citric acid cycle can begin • Pyruvate must first be converted to acetyl CoA, which links the citric acid cycle to glycolysis Acetyl group= unstable Uses active transport Diffuses out of cell

  29. The Kreb’s Cycle • Also called the “Tricarboxylic Acid Cycle”or the“Citric Acid cycle” • NAD+ and FAD (both are coenzymes) = electron “carriers”; proton acceptors • They are reduced and carry e-’s from Citric cycle to ETC • Dehydrogenase catalyzes hydrogen transfer reaction

  30. NAD+ and FAD Oxidized Form Reduced Form NAD+ NADH (2 e-, 1 H) FAD FADH2(4 e-, 2 H) THINK: FADH2 come into play in the 2nd stage of cellular respiration; it is also the 2nd electron carrier 

  31. Pyruvate (from glycolysis,2 molecules per glucose) Glycolysis Citricacidcycle Oxidativephosphorylation ATP ATP ATP CO2 CoA NADH + 3 H+ Acetyle CoA CoA CoA Citricacidcycle 2 CO2 3 NAD+ FADH2 FAD 3 NADH + 3 H+ ADP + P i ATP Figure 9.11 An overview of the citric acid cycle (this occurs for EACH pyruvate molecule)

  32. The Kreb’s Cycle • Let’s take a closer look…. • Page 169 in textbook • 8 steps in citric cycle in MATRIX • 1 turn of cycle  2 reduced carbons enter  2 oxidized carbons leave

  33. Citric acid cycle Oxidative phosphorylation Glycolysis S CoA C O CH3 Acetyl CoA CoA SH O C COO– H2O NADH 1 COO– CH2 + H+ COO– CH2 COO– NAD+ Oxaloacetate C 8 COO– HO CH2 2 CH2 HC COO– COO– COO– HO CH HO CH Malate Citrate COO– CH2 Isocitrate COO– CO2 Citric acid cycle 3 H2O 7 NAD+ COO– NADH COO– CH + H+ Fumarate CH2 CoA SH HC a-Ketoglutarate CH2 COO– C O 4 6 SH CoA COO– COO– COO– CH2 5 CH2 FADH2 CO2 CH2 CH2 NAD+ FAD C O COO– Succinate NADH CoA P i S + H+ Succinyl CoA GDP GTP ADP ATP Figure 9.12 Figure 9.12

  34. Kreb’s Cycle Summary • pyruvate  Acetyl-CoA + 1 NADH • Each turn of cycle uses 1 pyruvate • So… 1 glucose molecule produces 2 turns of Kreb’s cycle • 1 turn of cycle yields 4 NADH, 1 ATP, and 1 FADH2 and 3 CO2 (as waste product) Remember to multiply by 2…why? • http://www.hippocampus.org/AP%20Biology%20II • Watch Pyruvate

  35. Stage #3: Oxidative Phosphorylation(Electron Transport Chain (ETC) + Chemiosmosis) • Chemiosmosiscouples electron transport to ATP synthesis • NADH and FADH2 • Donate e-s to ETC, which powers ATP synthesis using oxidative phosphorylation **OCUURS IN CRISTAE (folds of inner membrane)

  36. What is “oxidative phosphorylation”? • Recall… • Take H+/e-s away, molecule = “oxidized” • Give H+/e-s, molecule = “reduced” • Give phosphate, molecule = “phosphorylated” • So…oxidative phosphorylation = process that couples removal of H+’s/ e-’s from one molecule & giving phosphate molecules to another molecule

  37. The Pathway of Electron Transport • In the ETC… • e-s from NADH and FADH2 lose energy in several steps **NEEDS O2 TO PROCEED (unlike glycolysis)

  38. ETC Characteristics • Lots of proteins (cytochromes) in cristae  increases surface area • 1000’s (many) copies of ETC • ETC carries e-’s from NADH/FADH2 O2 • O2 = pulls e-s “down” ETC due to electronegativity (high affinity for e-s)

  39. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesishttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesis Inner Mitochondrial membrane Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complex of electron carriers Intermembrane space Q IV I III ATP synthase II Inner mitochondrial membrane H2O FADH2 2 H+ + 1/2 O2 FAD+ NADH+ NAD+ ATP ADP + P i (Carrying electrons from, food) H+ Mitochondrial matrix Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Oxidativephosphorylation Figure 9.15 Protin motive force is used! • Chemiosmosis and the electron transport chain

  40. What happens at the end of the ETC chain? • At the end of the chain • Electrons are passed to oxygen, forming water • O2 = final e- acceptor • NAD delivers e- higher than FAD  NAD provides 50% more ATP

  41. ETC is a Proton (H+) Pump • Uses the energy from “falling” e-s (exergonic flow) to pump H+’s from matrix  to outer compartment • A H+ (proton) gradient forms inside mitochondria • ETC does NOT make ATP directly but provides stage for CHEMIOSOMOSIS to occur

  42. RECALL…Chemiosmosis • Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work • Uses ATP synthase • Makes ~90% of ATP in Cell Resp. • Proposed by Peter Mitchell (1961)

  43. A rotor within the membrane spins clockwise whenH+ flows past it down the H+ gradient. INTERMEMBRANE SPACE H+ H+ H+ H+ H+ H+ H+ A protein anchoredin the membraneholds the knobstationary. A rod (or “stalk”)extending into the rotor/ knob alsospins, activatingcatalytic sites inthe knob. H+ Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. ADP + ATP P i MITOCHONDRIAL MATRIX Figure 9.14 Chemiosmosis: The Energy-Coupling Mechanism • ATP synthase • Is the enzyme that actually makes ATP http://www.sigmaaldrich.com/life-science/metabolomics/learning-center/metabolic-pathways/atp-synthase.html

  44. A Comparison of Chemiosmosis in Chloroplasts and Mitochondria • Chloroplasts and mitochondria • Generate ATP by the SAME basic mechanism: chemiosmosis • But use different sources of energy to accomplish this • http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/atpase_flash.html

  45. The spatial organization of chemiosmosis • Differs in chloroplasts and mitochondria • In both organelles • electron transport chains generate a H+ gradient across a membrane • ATP synthase • Uses this proton-motive force to make ATP

  46. At certain steps along the ETC • Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix  intermembrane space • Inside (matrix) = low [H+] • Outside = high [H+]

  47. The resulting H+ gradient… • Stores energy • Drives chemiosmosis in ATP synthase • Is referred to as a proton-motive force

  48. Electron shuttles span membrane MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 FADH2 2 NADH 2 NADH 6 NADH Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA 2 Pyruvate Glucose + 2 ATP + about 32 or 34 ATP by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation About 36 or 38 ATP Maximum per glucose: Figure 9.16 • There are three main processes in this metabolic enterprise + 2 ATP

  49. About 40% of the energy in a glucose molecule • Is transferred to ATP during cellular respiration, making ~36- 38 ATP

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