ATP ATP. Cellular Respiration Harvesting Chemical Energy. The point is to make ATP!

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1 ellular Respiration Harvesting hemical Energy 1 The point is to make! 2 Harvesting stored energy Energy is stored in organic molecules carbohydrates, fats, proteins Heterotrophs eat these organic molecules food digest organic molecules to get raw materials for synthesis fuels for energy controlled release of energy burning fuels in a series of step-by-step enzyme-controlled reactions 3

2 Harvesting stored energy Glucose is the model catabolism of glucose to produce respiration glucose + oxygen carbon + water + energy dioxide 6 H H heat MBUSTIN = making a lot of heat energy by burning fuels in one step fuel (carbohydrates) H 2 + heat RESPIRATIN = making (& some heat) by burning fuels in many small steps glucose enzymes H 2 + (+ heat) 4 How do we harvest energy from fuels? Digest large molecules into smaller ones break bonds & move electrons from one molecule to another as electrons move they carry energy with them that energy is stored in another bond, released as heat or harvested to make loses e- gains e- oxidized reduced e - e - oxidation redox e - reduction 5 How do we move electrons in biology? Moving electrons in living systems electrons cannot move alone in cells electrons move as part of H atom move H = move electrons loses e- gains e- oxidized reduced H oxidation oxidation e p H reduction 6 H H 2 + H e - reduction 6

3 oupling oxidation & reduction REDX reactions in respiration release energy as breakdown organic molecules break - bonds strip off electrons from -H bonds by removing H atoms 6 H = the fuel has been oxidized electrons attracted to more electronegative atoms in biology, the most electronegative atom? 2 H 2 = oxygen has been reduced couple REDX reactions & use the released energy to synthesize oxidation 6 H H 2 + reduction 7 xidation & reduction xidation loss of electrons removing H releases energy exergonic Reduction gain of electrons adding H stores energy endergonic oxidation 6 H H 2 + reduction 8 Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around NAD + (reduced) NAD + nicotinamide Vitamin B3 niacin P FAD +2 FADH 2 (reduced) H N + NH 2 + H reduction oxidation P H H N + NH 2 phosphates P adenine P ribose sugar carries electrons as a reduced molecule 9

4 verview of cellular respiration 4 metabolic stages Anaerobic respiration 1. Glycolysis respiration without 2 in cytosol Aerobic respiration respiration using 2 in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain 6 H H ( + heat ) 10 The point is to make! 11 ellular respiration - overview 12

5 13 ellular Respiration Stage 1: Glycolysis 14 Glycolysis Breaking down glucose glyco lysis (splitting sugar) glucose pyruvate 6 2x 3 In the cytosol? Why does that make evolutionary sense? ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to still is starting point for ALL cellular respiration but it s inefficient generate only 2 for every 1 glucose occurs in cytosol (liquid of the cytoplasm) 15

6 Evolutionary perspective Prokaryotes first cells had no organelles Anaerobic atmosphere life on Earth first evolved without free oxygen ( 2 ) in atmosphere energy had to be captured from organic molecules in absence of 2 Prokaryotes that evolved glycolysis are ancestors of all modern life ALL cells still utilize glycolysis 16 1st half of glycolysis (5 reactions) Glucose priming get glucose ready to split phosphorylate glucose molecular rearrangement split destabilized glucose energy investment phase (Use 2 ) P H 2 H 2 H NAD + Glucose 1 hexokinase ADP Glucose 6-phosphate 2 6 phosphoglucose isomerase Fructose 6-phosphate ADP 3 phosphofructokinase Fructose 1,6-bisphosphate 4,5 aldolase isomerase Dihydroxyacetone phosphate P i 1,3-Bisphosphoglycerate (BPG) P i glyceraldehyde 3-phosphate dehydrogenase Glyceraldehyde 3 -phosphate (G3P) NAD + 1,3-Bisphosphoglycerate (BPG) P P H 2 H H 2 P H 2 H 2 H HH H 2 P HH H 2 P P H 2 H H 2 P 17 2nd half of glycolysis (5 reactions) Energy Harvest production G3P donates H oxidizes the sugar reduces NAD + NAD + production G3P pyruvate PEP sugar donates P substrate level phosphorylation ADP NAD + ADP 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) H 2 7 phosphoglycerate kinase 8 phosphoglyceromutase 9 enolase Phosphoenolpyruvate (PEP) ADP DHAP P--- Pyruvate P i 6 10 pyruvate kinase G3P ---P P i 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) Pyruvate H 2 NAD + ADP ADP - HH H 2 P - H P H 2 H - H 2 P - H 3 18

7 Energy accounting of glycolysis 2 2 ADP glucose pyruvate 6 2x 3 4 ADP 4 2 NAD + 2 Net gain = some energy investment (-2 ) small energy return (4 + 2 ) 1 6 sugar 2 3 pyruvate 19 Substrate-level Phosphorylation In the last steps of glycolysis, where did the P come from to make? the sugar substrate (PEP) P is transferred from PEP to ADP kinase enzyme ADP H 2 9 enolase Phosphoenolpyruvate (PEP) ADP Pyruvate 10 pyruvate kinase Phosphoenolpyruvate (PEP) Pyruvate H 2 ADP - H 2 - H 3 P The P i came directly from the substrate! therefore... substrate level phosphorylation Is that all there is? Not a lot of energy for 1 billon years + this is how life on Earth survived no 2 = slow growth, slow reproduction only harvest 3.5% of energy stored in glucose more carbons to strip off = more energy to harvest 2 2 glucose pyruvate 6 2x

8 Glycolysis summary ENERGY INVESTMENT endergonic invest some -2 ENERGY PAYFF G3P ---P 4 exergonic harvest a little & a little NET YIELD like $$ in the bank net yield Pyruvate is a branching point Pyruvate 2 2 fermentation anaerobic respiration mitochondria Krebs cycle aerobic respiration 23 How is recycled to NAD +? Another molecule must accept H from H 2 with oxygen aerobic respiration NAD + pyruvate without oxygen anaerobic respiration fermentation 2 recycle 2 which path you use depends on who you are acetyl-oa Krebs cycle NAD + lactate lactic acid fermentation acetaldehyde NAD + ethanol alcohol fermentation 24

9 Fermentation (anaerobic) Bacteria, yeast pyruvate ethanol NAD + beer, wine, bread back to glycolysis Animals, some fungi pyruvate lactic acid 3 3 NAD + cheese, anaerobic exercise (no 2 ) back to glycolysis 25 Alcohol Fermentation pyruvate ethanol NAD + back to glycolysis Dead end process at ~12% ethanol, kills yeast can t reverse the reaction bacteria yeast recycle 26 Lactic Acid Fermentation pyruvate lactic acid 3 3 NAD + Reversible process once 2 is available, lactate is converted back to pyruvate by the liver 2 back to glycolysis animals some fungi recycle 27

10 Pyruvate is a branching point Pyruvate 2 2 fermentation anaerobic respiration mitochondria Krebs cycle aerobic respiration 28 ellular Respiration Stage 2 & 3: xidation of Pyruvate Krebs ycle 29 The point is to make! 30

11 ellular respiration 31 Glycolysis is only the start Glycolysis glucose 2 pyruvate 6 2x 3 Pyruvate has more energy to yield 3 more to strip off (to oxidize) if 2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to 2 pyruvate x 1 32 Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins matrix fluid-filled space between membranes 33

12 Mitochondria Structure Double membrane energy harvesting organelle smooth outer membrane highly folded inner membrane intermembrane space matrix have own DNA, ribosomes enzymes cristae fluid-filled space between membranes inner fluid-filled space intermembrane free in matrix & membrane-bound space outer membrane inner membrane cristae matrix What cells would have a lot of mitochondria? mitochondrial DNA Mitochondria Function 34 Form fits function! Dividing mitochondria Membrane-bound proteins Who else divides like that? Enzymes bacteria! What does this tell us about the evolution of eukaryotes? Endosymbiosis Advantage of highly folded inner membrane? More surface area for membranebound enzymes xidation of pyruvate Pyruvate enters mitochondrial matrix [ 2x pyruvate acetyl oa NAD 35 ] 3 step oxidation process releases 2 2 (count the carbons!) reduces 2 NAD 2 (moves e-) produces 2 acetyl oa Acetyl oa enters Krebs cycle 36

13 Pyruvate oxidized to Acetyl oa NAD + reduction Pyruvate -- 2 oenzyme A oxidation Acetyl oa - 2 x [ Yield = 2 sugar + NAD 2 ] 37 Krebs cycle aka itric Acid ycle in mitochondrial matrix 8 step pathway each catalyzed by specific enzyme step-wise catabolism of 6 citrate molecule Evolved later than glycolysis does that make evolutionary sense? bacteria 3.5 billion years ago (glycolysis) free billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria) Hans Krebs

14 ount the carbons! pyruvate acetyl oa 6 citrate This happens twice for each glucose molecule 4 4 oxidation of sugars x ount the electron carriers! pyruvate acetyl oa citrate 2 This happens twice for each glucose molecule 4 4 reduction of electron carriers x FADH So we fully oxidized glucose 6 H & ended up with only... 4! 42

15 Electron arriers = Hydrogen arriers Krebs cycle produces large quantities of electron carriers FADH 2 go to Electron Transport hain! ADP + P i H+ 43 Energy accounting of Krebs cycle 4 NAD + 1 FAD 4 NAD 1 FADH 2 2x Acetyl oa 2 2 2x 1 1 ADP 1 Net gain = 2 = 8 NAD 2 FADH 2 44 Value of Krebs cycle? If the yield is only 2 then how was the Krebs cycle an adaptation? value of & FADH 2 electron carriers & H carriers reduced molecules move electrons reduced molecules move ions to be used in the Electron Transport hain 45

16 46 ellular Respiration Stage 4: Electron Transport hain 47 The point is to make! 48

17 ellular respiration accounting so far Glycolysis 2 Kreb s cycle 2 Life takes a lot of energy to run, need to extract more energy than 4! There s got to be a better way! A working muscle recycles over 10 million s per second 51

18 There is a better way! Electron Transport hain series of proteins built into inner memebrane along cristae transport proteins & enzymes transport of electrons down ET linked to pumping of to create gradient yields 34 from 1 glucose! only in presence of 2 (final electron acceptor) 52 Electron Transport hain Q FADH 2 dehydrogenase Mitochondrial matrix cytochrome bc complex cytochrome c oxidase complex 53 Remember the Electron arriers? Glycolysis glucose G3P Krebs cycle FADH 2 1 = 3 1 FADH 2 = 2 54

19 55 Electron Transport hain NAD + + H e p H e- + Q e FADH 2 H NAD + dehydrogenase H e FAD Building proton gradient! cytochrome bc complex e intermembrane space inner mitochondrial membrane H 2 cytochrome c oxidase complex mitochondrial matrix What powers the proton ( ) pumps? 56 Stripping H from Electron arriers Electron carriers pass electrons & to ET H cleaved off & FADH 2 electrons stripped from H atoms (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ET) flowing electrons = energy to do work transport proteins in membrane pump H + (protons) across inner membrane to intermembrane space H+ Q e FADH 2 NAD + dehydrogenase e FAD cytochrome bc complex e H 2 cytochrome c oxidase complex ADP + P i 57

20 But what pulls the electrons down the ET? oxygen 2 58 Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy 59 hemiosmosis build up of proton gradient just so H+ can flow through synthase enzyme to build 60

21 proton-motive force Set up a gradient Allow the protons to flow through synthase Synthesizes ADP + P i ADP + P i Peter Mitchell Proposed chemiosmotic hypothesis revolutionary idea at the time proton motive force

22 Pyruvate from cytoplasm Inner mitochondrial membrane Q Intermembrane space Electron transport system e - 2. Electrons provide energy Acetyl-oA 1. Electrons are harvested to pump protons and carried to the transport across the system. membrane. Krebs cycle 2 FADH 2 e - e - 3. xygen joins with protons to form water. H e Mitochondrial matrix 4. Protons diffuse back in down their concentration gradient, driving the synthesis of. synthase 64 ellular respiration ~38 65 Summary of cellular respiration 6 H H 2 + ~40 Where did the glucose come from? Where did the 2 come from? Where did the 2 come from? Where did the 2 go? Where did the H 2 come from? Where did the come from? What else is produced that is not listed in this equation? 66

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