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Cellular Respiration Harvesting Chemical Energy ATP AP Biology 2006-2007 Harvesting stored energy Glucose is the model respiration catabolism of glucose to produce ATP glucose + oxygen energy + water + carbon dioxide C6H12O6 + 6O2 ATP + 6H2O + 6CO2 + heat COMBUSTION = making a lot of heat energy by burning fuels in one step fuel AP Biology carbohydrates) RESPIRATION = making ATP (& some heat) by burning fuels in many small steps ATP enzymes O2 ATP O2 CO2 + H2O + ATP (+ heat) glucose CO2 + H2O + heat 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 ATP loses e- gains e- + oxidized reduced + + eoxidation AP Biology e- – ereduction redox 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 e p move H = move electrons loses e- gains e- oxidized + + oxidation reduced + – H reduction H oxidation C6H12O6 + AP Biology H e- 6O2 6CO2 + 6H2O + ATP reduction Coupling oxidation & reduction REDOX reactions in respiration release energy as breakdown organic molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms C6H12O6 CO2 = the fuel has been oxidized electrons attracted to more electronegative atoms in biology, the most electronegative atom? O2 H2O = oxygen has been reduced O couple REDOX reactions & 2 use the released energy to synthesize ATP oxidation C6H12O6 + AP Biology 6O2 6CO2 + 6H2O + ATP reduction Oxidation & reduction Oxidation Reduction adding O removing H loss of electrons releases energy exergonic removing O adding H gain of electrons stores energy endergonic oxidation C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction AP Biology like $$ in the bank Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around NAD+ NADH (reduced) FAD+2 FADH2 (reduced) NAD+ nicotinamide Vitamin B3 niacin O– O – P –O O phosphates O– O – P –O O AP Biology H reducing power! NADH O H H C NH2 N+ + adenine ribose sugar C NH2 reduction O– – – oxidation O P O O O– O – P –O O carries electrons as H O a reduced molecule N+ How efficient! Build once, use many ways Overview of cellular respiration 3 metabolic stages Anaerobic respiration 1. Glycolysis respiration without O2 in cytosol Aerobic respiration respiration using O2 in mitochondria 2. Krebs cycle 3. Electron transport chain C H O6 + AP Biology 6 12 6O2 ATP + 6H2O + 6CO2 (+ heat) Cellular Respiration Stage 1: Glycolysis AP Biology 2007-2008 Glycolysis Breaking down glucose “glyco – lysis” (splitting sugar) glucose pyruvate 2x 3C 6C ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to ATP still is starting point for ALL cellular respiration but it’s inefficient generate only 2 ATP for every 1 glucose occurs in cytosol AP Biology That’s not enough ATP for me! In the cytosol? Why does that make evolutionary sense? Evolutionary perspective Prokaryotes first cells had no organelles Enzymes of glycolysis are “well-conserved” Anaerobic atmosphere life on Earth first evolved without free oxygen (O2) in atmosphere energy had to be captured from organic molecules in absence of O2 Prokaryotes that evolved glycolysis are ancestors of all modern life AP Biology ALL cells still utilize glycolysis You mean we’re related? Do I have to invite them over for the holidays? Overview glucose C-C-C-C-C-C 10 reactions enzyme 2 ATP enzyme 2 ADP convert fructose-1,6bP glucose (6C) to P-C-C-C-C-C-C-P enzyme enzyme 2 pyruvate (3C) enzyme DHAP G3P produces: 4 ATP & 2 NADH P-C-C-C C-C-C-P 2H consumes: 2Pi enzyme 2 ATP enzyme net yield: 2Pi enzyme 2 ATP & 2 NADH DHAP = dihydroxyacetone phosphate AP Biology G3P = glyceraldehyde-3-phosphate pyruvate C-C-C 2 NAD+ 2 4 ADP 4 ATP Glycolysis summary endergonic invest some ATP ENERGY INVESTMENT -2 ATP ENERGY PAYOFF G3P C-C-C-P 4 ATP exergonic harvest a little ATP & a little NADH like $$ in the bank NET YIELD AP Biology net yield 2 ATP 2 NADH 1st half of glycolysis (5 reactions) Glucose “priming” get glucose ready to split phosphorylate CH2 O O P Glucose 6-phosphate 2 P O ADP CH2 O O P CH2 CH2 CH2OH O Fructose 1,6-bisphosphate O CH2 C 4,5 aldolase isomerase O Dihydroxyacetone CH2OH phosphate Glyceraldehyde 3 -phosphate (G3P) Pi NAD+ Pi 6 glyceraldehyde NADH NADH 3-phosphate P dehydrogenase 1,3-Bisphosphoglycerate 1,3-Bisphosphoglycerate (BPG) (BPG) H C O CHOH CH2 O NAD+ AP Biology O Fructose 6-phosphate 3 ATP phosphofructokinase split destabilized glucose P ADP phosphoglucose isomerase glucose molecular rearrangement CH2OH Glucose 1 ATP hexokinase O P O CHOH CH2 O P O P 2nd half of glycolysis (5 reactions) DHAP P-C-C-C Energy Harvest NADH production G3P donates H oxidizes the sugar reduces NAD+ NAD+ NADH NAD+ Pi phosphorylation” ADP ATP AP Biology NAD+ NADH 7 phosphoglycerate kinase ADP ATP 3-Phosphoglycerate (3PG) ADP ATP 3-Phosphoglycerate (3PG) 8 phosphoglyceromutase 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) CHOH CH2 O P C O H C O CH2OH P OH2O Phosphoenolpyruvate (PEP) 10 pyruvate kinase ADP ATP Pyruvate C C O O CH2 OC ATP Pyruvate OC O- 2-Phosphoglycerate (2PG) 9 enolase H2O ADP Payola! Finally some ATP! Pi 6 NADH ATP production G3P pyruvate PEP sugar donates P “substrate level G3P C-C-C-P O C O CH3 P Substrate-level Phosphorylation In the last steps of glycolysis, where did the P come from to make ATP? 9 the sugar substrateH O(PEP) enolase OH2O 2 P is transferred from PEP to ADP kinase enzyme ADP ATP AP Biology Phosphoenolpyruvate (PEP) ADP Phosphoenolpyruvate (PEP) 10 pyruvate kinase Pyruvate I get it! The Pi came directly from the substrate! Pyruvate C CH2 O O OC ATP ATP ATP ADP C O C O CH3 P Energy accounting of glycolysis 2 ATP 2 ADP glucose pyruvate 2x 3C 6C 4 ADP 4 ATP 2 NAD+ 2 Net gain = 2 ATP + 2 NADH All that work! And that’s all I get? But glucose has so much more to give! some energy investment (-2 ATP) small energy return (4 ATP + 2 NADH) AP 1Biology 6C sugar 2 3C sugars Cellular Respiration Stage 2: Citric Acid Cycle or Krebs Cycle AP Biology 2006-2007 Glycolysis is only the start Glycolysis glucose pyruvate 6C 2x 3C Pyruvate has more energy to yield 3 more C to strip off (to oxidize) if O2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to CO2 pyruvate CO2 AP Biology 3C 1C Cellular respiration AP Biology 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 & What cells would have AP Biology a lot of mitochondria? outer intermembrane membrane inner membrane-bound space membrane cristae matrix mitochondrial DNA Mitochondria – Function Oooooh! Form fits function! Dividing mitochondria Membrane-bound proteins Who else divides like that? Enzymes & permeases bacteria! What does this tell us about the evolution of eukaryotes? Endosymbiosis! AP Biology Advantage of highly folded inner membrane? More surface area for membranebound enzymes & permeases Oxidation of pyruvate Pyruvate enters mitochondrial matrix [ 2x pyruvate acetyl CoA + CO2 3C 2C 1C NAD Where does the CO2 go? Exhale! 3 step oxidation process releases 2 CO2 (count the carbons!) reduces 2 NAD 2 NADH (moves e ) produces 2 acetyl CoA Acetyl CoA enters Krebs cycle AP Biology ] Pyruvate oxidized to Acetyl CoA reduction NAD+ Pyruvate C-C-C [ Coenzyme A CO2 Acetyl CoA C-C oxidation 2 x Yield = 2C sugar + NADH + CO2 AP Biology ] Citric Acid cycle 1937 | 1953 aka Krebs Cycle in mitochondrial matrix 8 step pathway Hans Krebs each catalyzed by specific enzyme 1900-1981 step-wise catabolism of 6C citrate molecule Evolved later than glycolysis does that make evolutionary sense? bacteria 3.5 billion years ago (glycolysis) free O2 2.7 billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic AP Biology respiration = organelles mitochondria) Count the carbons! pyruvate 3C 2C 6C 4C This happens twice for each glucose molecule 4C citrate oxidation of sugars 4C 6C CO2 x2 4C AP Biology acetyl CoA 5C 4C CO2 Count the electron carriers! pyruvate 3C 6C 4C NADH This happens twice for each glucose molecule 2C 4C citrate reduction of electron carriers x2 4C FADH2 4C AP Biology acetyl CoA ATP CO2 NADH 6C CO2 NADH 5C 4C CO2 NADH Whassup? So we fully oxidized glucose C6H12O6 CO2 & ended up with 4 ATP! What’s the point? AP Biology Electron Carriers = Hydrogen Carriers H+ Citric Acid cycle produces large quantities of electron carriers NADH FADH2 go to Electron Transport Chain! AP Biology What’s so important about electron carriers? H+ H+ H+ + H+ H H+ H+ ADP + Pi ATP H+ Energy accounting of Citric Acid cycle 4 NAD + 1 FAD 4 NADH + 1 FADH2 2x pyruvate CO2 3C 3x 1C 1 ADP 1 ATP ATP Net gain = 2 ATP = 8 NADH + 2 FADH2 AP Biology Value of Citric Acid cycle? If the yield is only 2 ATP then how was the Citric Acid cycle an adaptation? value of NADH & FADH2 electron carriers & H carriers reduced molecules move electrons reduced molecules move H+ ions to be used in the Electron Transport Chain like $$ in the bank AP Biology