Cellular Respiration Harvesting Chemical Energy. ATP. glucose + oxygen energy + water + carbon. dioxide. respiration. ATP. +. 6H 2 O. +. 6CO 2. + heat. . C 6 H 12 O 6. +. 6O 2. COMBUSTION = making a lot of heat energy by burning fuels in one step. ATP. glucose. O 2.
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glucose + oxygen energy + water + carbon dioxide respiration ATP + 6H2O + 6CO2 + heat C6H12O6 + 6O2 COMBUSTION = making a lot of heat energy by burning fuels in one step ATP glucose O2 O2 fuel(carbohydrates) Harvesting stored energy • Glucose is the model • catabolism of glucose to produce ATP RESPIRATION = making ATP (& some heat)by burning fuels in many small steps ATP enzymes CO2 + H2O + heat CO2 + H2O + ATP (+ heat)
+ + oxidation reduction e- 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 + – e- e- redox
e p loses e- gains e- oxidized reduced + – + + H oxidation reduction H C6H12O6 + 6O2 6CO2 + 6H2O + ATP H 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 oxidation reduction e-
oxidation C6H12O6 + 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 • C6H12O6CO2 =thefuel has been oxidized • electrons attracted to more electronegative atoms • in biology, the most electronegative atom? • O2H2O =oxygen has been reduced • couple REDOX reactions & use the released energy to synthesize ATP O2
Oxidation adding O removing H loss of electrons releases energy exergonic Reduction removing O adding H gain of electrons stores energy endergonic oxidation C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction Oxidation & reduction
like $$in the bank O– O– O– O– P P P P –O –O –O –O O– O– O– O– O O O O NAD+ nicotinamide Vitamin B3 niacin O O H H C C NH2 C C NH2 How efficient! Build once,use many ways N+ N+ reduction + H oxidation phosphates adenine ribose sugar Moving electrons in respiration • Electron carriers move electrons by shuttling H atoms around • NAD+NADH (reduced) • FAD+2FADH2 (reduced) reducing power! NADH H carries electrons as a reduced molecule
C6H12O6 + 6O2 ATP + 6H2O + 6CO2 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 (+ heat)
glucose pyruvate 6C 3C 2x Glycolysis • Breaking down glucose • “glyco – lysis” (splitting sugar) • 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 only2 ATP for every 1 glucose • occurs in cytosol In thecytosol?Why doesthat makeevolutionarysense? That’s not enoughATP for me!
Evolutionary perspective Enzymesof glycolysis are“well-conserved” • Prokaryotes • first cells had no organelles • Anaerobic atmosphere • life on Earth first evolved withoutfree 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 • ALL cells still utilize glycolysis You meanwe’re related?Do I have to invitethem over for the holidays?
enzyme enzyme enzyme enzyme enzyme enzyme enzyme enzyme ATP ATP 4 2 4 2 2 ADP NAD+ ADP 2Pi 2 2H 2Pi glucose C-C-C-C-C-C Overview 10 reactions • convert glucose (6C)to 2 pyruvate (3C) • produces:4 ATP & 2 NADH • consumes:2 ATP • net yield:2 ATP & 2 NADH fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P pyruvate C-C-C DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate
Glycolysis summary endergonic invest some ATP ENERGY INVESTMENT -2 ATP G3P C-C-C-P exergonic harvest a little ATP & a little NADH ENERGY PAYOFF 4 ATP like $$in the bank • net yield • 2 ATP • 2 NADH NET YIELD
1st half of glycolysis (5 reactions) CH2OH Glucose “priming” O Glucose 1 ATP hexokinase • get glucose ready to split • phosphorylate glucose • molecular rearrangement • split destabilized glucose ADP CH2 O P O Glucose 6-phosphate 2 phosphoglucose isomerase CH2 P O CH2OH O Fructose 6-phosphate 3 ATP phosphofructokinase P O CH2 CH2 O P O ADP Fructose 1,6-bisphosphate aldolase 4,5 H O CH2 P isomerase C O C O Dihydroxyacetone phosphate Glyceraldehyde 3 -phosphate (G3P) CHOH CH2OH CH2 O P NAD+ Pi NAD+ Pi 6 glyceraldehyde 3-phosphate dehydrogenase NADH NADH P O O CHOH 1,3-Bisphosphoglycerate (BPG) 1,3-Bisphosphoglycerate (BPG) CH2 O P
2nd half of glycolysis (5 reactions) DHAP P-C-C-C G3P C-C-C-P Energy Harvest • NADH production • G3P donates H • oxidizes the sugar • reduces NAD+ • NAD+ NADH • ATP production • G3P pyruvate • PEP sugar donates P • “substrate level phosphorylation” • ADP ATP Pi Pi NAD+ NAD+ 6 NADH NADH 7 ADP ADP O- phosphoglycerate kinase C ATP ATP CHOH 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) CH2 P O 8 O- phosphoglycero-mutase O C H C O P 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) CH2OH O- 9 H2O H2O enolase C O O C P Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) CH2 O- 10 ADP ADP C O pyruvate kinase Payola!Finally some ATP! ATP ATP C O CH3 Pyruvate Pyruvate
O- 9 H2O H2O enolase C O O C P Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) CH2 O- 10 ADP ADP C O pyruvate kinase ATP ATP C O CH3 Pyruvate Pyruvate Substrate-level Phosphorylation • In the last steps of glycolysis, where did the P come from to make ATP? • the sugar substrate (PEP) • P is transferred from PEP to ADP • kinase enzyme • ADP ATP ATP I get it! The Pi camedirectly fromthe substrate!
2 ATP 2 ADP 2 NAD+ 4 ADP ATP 4 2 Energy accounting of glycolysis • Net gain = 2 ATP + 2 NADH • some energy investment (-2 ATP) • small energy return (4 ATP + 2 NADH) • 1 6C sugar 2 3C sugars glucose pyruvate 6C 3C 2x All that work! And that’s all I get? Butglucose hasso much moreto give!
glucose pyruvate 6C 3C 2x pyruvate CO2 Glycolysis is only the start • Glycolysis • 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 3C 1C
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?
Oooooh!Form fits function! Mitochondria – Function Dividing mitochondria Who else divides like that? Membrane-bound proteins Enzymes & permeases bacteria! Advantage of highly folded inner membrane? More surface area for membrane-bound enzymes & permeases What does this tell us about the evolution of eukaryotes? Endosymbiosis!
[ ] 2x pyruvate acetyl CoA + CO2 NAD Oxidation of pyruvate • Pyruvate enters mitochondrial matrix • 3 step oxidation process • releases 2 CO2(count the carbons!) • reduces 2NAD 2 NADH (moves e-) • produces 2acetyl CoA • Acetyl CoA enters Krebs cycle 1C 3C 2C Wheredoes theCO2 go? Exhale!
NAD+ 2 x [ ] Pyruvate oxidized to Acetyl CoA reduction Acetyl CoA Coenzyme A CO2 Pyruvate C-C C-C-C oxidation Yield = 2C sugar + NADH + CO2
1937 | 1953 Citric Acid cycle • aka Krebs Cycle • in mitochondrial matrix • 8 step pathway • each catalyzed by specific enzyme • step-wise catabolism of 6C citrate molecule • Evolved later than glycolysis • does that make evolutionary sense? • bacteria 3.5 billion years ago (glycolysis) • free O22.7 billion years ago (photosynthesis) • eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria) Hans Krebs 1900-1981
2C 6C 5C 4C 3C 4C 4C 4C 4C 6C CO2 CO2 Count the carbons! pyruvate acetyl CoA citrate oxidationof sugars This happens twice for each glucose molecule x2
2C 6C 5C 4C 3C 4C 6C 4C 4C 4C NADH ATP CO2 CO2 CO2 NADH NADH FADH2 NADH Count the electron carriers! pyruvate acetyl CoA citrate reductionof electroncarriers This happens twice for each glucose molecule x2
Whassup? So we fully oxidized glucose C6H12O6 CO2 & ended up with 4 ATP! What’s the point?
H+ H+ H+ H+ H+ H+ H+ H+ H+ Electron Carriers = Hydrogen Carriers • Citric Acid cycle produces large quantities of electron carriers • NADH • FADH2 • go to Electron Transport Chain! ADP+ Pi ATP What’s so important about electron carriers?
4 NAD+1 FAD 4 NADH+1FADH2 2x 1C 3x 1 ADP 1 ATP Energy accounting of Citric Acid cycle Net gain = 2 ATP = 8 NADH + 2 FADH2 pyruvate CO2 3C ATP
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