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http://www.youtube.com/watch?v=VCpNk92uswY What’s the point? Cellular Respiration The point Stage 4: is to make ATP! Electron Transport Chain ATP AP Biology 2013-2014 Cellular respiration AP Biology ATP accounting so far… Glycolysis 2 ATP Kreb’s cycle 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! Even we need a lot more ATP! AP Biology There’s got to be a better way! I need a lot more ATP! A working muscle recycles over 10 million ATPs per second There is a better way! Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradient yields ~36 ATP from 1 glucose! only in presence of O 2 (aerobic respiration) AP Biology That sounds more like it! O2 Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space fluid-filled space between membranes AP Biology Oooooh! Form fits function! Electron Transport Chain Inner mitochondrial membrane Intermembrane space C Q NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex Mitochondrial matrix AP Biology Q = ubiquinone c = cytochrome c Remember the Electron Carriers? Glycolysis glucose Krebs cycle G3P 2 NADH 2x =2 8 NADH 2 FADH2 Time to break open the piggybank! x2 = 6 AP Biology Electron Transport Chain H+ H+ H+ H+ H e- + H+ H+ C e– NAD+ NADH dehydrogenase intermembrane space inner mitochondrial membrane e– H FADH2 H+ e– Q AP Biology H+ H+ NADH H H+ Building proton gradient! NADH NAD+ + H e p H+ FAD 2H+ + cytochrome bc complex 1 2 O2 H 2O cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps?… e– e– NADH NAD+ + H Stripping H from Electron Carriers Electron carriers pass electrons & H+ to ETC H cleaved off NADH & FADH2 electrons stripped from H atoms H+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) flowing electrons = energy to do work H e- + H+ transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space TA-DA!! Moving electrons do the work! H+ + H+ + H+ H H H H+ + H+ H + H+ H H+ H+ C Q e– NADH AP Biology + H+ FADH2 NAD+ NADH dehydrogenase e– e– FAD 2H+ cytochrome bc complex + 1 2 O2 H2O cytochrome c oxidase complex ADP + Pi ATP H+ e p http://www.johnkyrk.com/mitochondrion.html But what “pulls” the electrons down the ETC? H2O O2 AP Biology electrons flow downhill to O2 oxidative phosphorylation Electron transport chain Consists of several protein complexes AP Biology Aren’t you glad you do not have to memorize this?? http://www.youtube.com/watch?v=QXhBJycQ7y0 http://www.youtube.com/watch?v=_lhVIbifKGU Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy make ATP instead of fire! AP Biology Figure 9.13 NADH 50 2 e NAD FADH2 Free energy (G) relative to O2 (kcal/mol) 2 e 40 FMN Fe S Fe S II Q III Cyt b 30 Multiprotein complexes FAD I Fe S Cyt c1 IV Cyt c Cyt a Cyt a3 20 10 2 e (originally from NADH or FADH2) 0 http://media.pearsoncmg.com/bc/bc_0media_bio/de mo/bioflix/bf_cellularrespiration_demo.html 2 H + 1/2 O2 H2 O http://www.youtube.com/watch?v=-zsEepV0N-I We did it! Set up a H+ “proton-motive” force H+ H+ H+ gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + Pi ATP Are we there yet? AP Biology H+ H+ H+ H+ H+ ADP + Pi ATP H+ Chemiosmosis: The Energy-Coupling Mechanism The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Electron transfer in the etc causes Chemiosmosis links the Electron Transport Chain to ATP synthesis proteins to pump H+ from the mitochondrial matrix to the intermembrane space H+ then moves back across the membrane, passing through the ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ADP to ATP This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work AP Biology So that’s the point! 1961 | 1978 Peter Mitchell Proposed chemiosmotic hypothesis revolutionary idea at the time proton motive force 1920-1992 AP Biology Pyruvate from cytoplasm Inner mitochondrial H+ membrane H+ Intermembrane space Electron transport C system Q NADH e- 1. Electrons are harvested and carried to the Acetyl-CoA transport system. NADH e- Krebs cycle FADH2 e- 2. Electrons provide energy to pump protons across the membrane. e- H2O 3. Oxygen joins with protons to form water. 1 O 2 +2 2H+ O2 H+ CO2 ATP Mitochondrial matrix AP Biology H+ ATP ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ ATP synthase Cellular respiration 2 ATP AP Biology + 2 ATP + ~36 ATP Summary of cellular respiration C6H12O6 + 6O2 6CO2 + 6H2O + ~40 ATP Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? AP Biology Taking it beyond… What is the final electron acceptor in H+ H+ H+ C Q Electron Transport Chain?e e– e– – NADH O2 FADH2 NAD+ NADH dehydrogenase FAD 2H+ + cytochrome bc complex 1 2 O2 H2O cytochrome c oxidase complex So what happens if O2 unavailable? ETC backs up nothing to pull electrons down chain NADH & FADH2 can’t unload H AP Biology ATP production ceases cells run out of energy and you die! Beyond glucose: Other carbohydrates Glycolysis accepts a wide range of carbohydrates fuels polysaccharides glucose hydrolysis ex. starch, glycogen other 6C sugars glucose modified ex. galactose, fructose AP Biology Beyond glucose: Proteins Proteins amino acids hydrolysis waste H O H | || N —C— C—OH | H R amino group = waste product excreted as ammonia, urea, or uric acid AP Biology glycolysis Krebs cycle carbon skeleton = enters glycolysis or Krebs cycle at different stages Beyond glucose: Fats Fats hydrolysis glycerol & fatty acids glycerol (3C) PGAL glycolysis fatty acids 2C acetyl acetyl Krebs groups coA cycle glycerol enters glycolysis as AP PGAL Biology fatty acids enter Krebs cycle as acetyl CoA Carbohydrates vs. Fats Fat generates 2x ATP vs. carbohydrate more C in gram of fat more O in gram of carbohydrate so it’s already partly oxidized fat carbohydrate AP Biology Metabolism Coordination of digestion & synthesis by regulating enzyme Digestion digestion of carbohydrates, fats & proteins all catabolized through same pathways enter at different points AP Biology cell extracts energy from every source CO2 Metabolism Coordination of digestion & synthesis by regulating enzyme Synthesis enough energy? build stuff! cell uses points in glycolysis & Krebs cycle as links to pathways for synthesis run the pathways “backwards” eat too much fuel, build fat pyruvate glucose Krebs cycle intermediaries AP Biology acetyl CoA amino acids fatty acids Cells are versatile & thrifty METABOLISM Chapter 8 An Introduction to Metabolism Metabolism = total of an organism’s chemical reactions AP Biology Glycan Metabolism Lipid Metabolism AP Biology Nucleotide Metabolism Carbohydrate Metabolism Amino Acid Metabolism Cofactors & Vitamins Control of Respiration Feedback Control AP Biology 2005- Feedback Inhibition Regulation & coordination of production production is self-limiting final product is inhibitor of earlier step allosteric inhibitor of earlier enzyme no unnecessary accumulation of product ABCDEFG 1 2 3 4 5 6 X enzyme enzyme enzyme enzyme enzyme enzyme AP Biology allosteric inhibitor of enzyme 1 Respond to cell’s needs Key points of control phosphofructokinase allosteric regulation of enzyme “can’t turn back” step before splitting glucose AMP & ADP stimulate ATP inhibits citrate inhibits Why is this regulation important? Balancing act: availability of raw materials vs. energy AP Biologydemands vs. synthesis Regulation Feedback mechanisms help regulate cellular respiration Ex. Feedback inhibition Phosphofructokinase (PFK) is the major enzyme in glycolysis that is controlled ATP, Citrate inhibits ADP, AMP stimulates AP Biology Versatility Glucose is not the only fuel that can be used in cellular respiration Other biomolecules can be converted into intermediates and used in cellular respiration AP Biology What’s the point? The point is to make ATP! ATP AP Biology 2013-2014