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glucose C-C-C-C-C-C 2 ATP OVERVIEW 2 ADP • 10 reactions fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P 2Pi 2H 2 NAD+ 2 2Pi pyruvate C-C-C 4 ADP 4 ATP • Convert glucose (6C) to 2 pyruvate (3C) • Produces: 4 ATP & 2 NADH • Consumes: 2 ATP • Net yield: 2 ATP & 2 NADH DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate CELLULAR RESPIRATION Stage 2 & 3: Oxidation of Pyruvate Also called Link Reaction Krebs Cycle GLYCOLYSIS IS ONLY THE START • Glycolysis glucose pyruvate 2x 3C 6C • Pyruvate has more energy to yield • 3 more C to strip off (oxidize) • If O2 is available, pyruvate enters mitochondria • Enzymes of Krebs cycle complete the full oxidation of sugar to CO2 pyruvate CO2 3C 1C CELLULAR RESPIRATION 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 outer intermembrane membrane inner space membrane cristae matrix What cells would have a lot of mitochondria? mitochondrial DNA Oooooh! Form fits function! MITOCHONDRIA - 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! Advantage of highly folded inner membrane? More surface area for membranebound enzymes & permeases MITOCHONDRIA - STRUCTURE • Pyruvate enters mitochondrial matrix [ 2x pyruvate acetyl CoA + CO2 3C 2C 1C ] NAD • • • • 3 step oxidation process Releases 2 CO2 Reduces 2 NAD 2NADH Produces 2 acetyl-CoA • Acetyl-CoA enters Krebs cycle Where does the CO2 go? Exhale! 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 ] KREBS CYCLE • aka Citric Acid 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 bya (glycolysis) • Free O2 2.7 bya (photosynthesis) • Eukaryotes 1.5 bya (aerobic prokaryote mitochondria = organelle) Hans Krebs 1900-1981 COUNT THE CARBONS pyruvate 3C 2C 6C 4C This happens twice for each glucose molecule 4C acetyl CoA citrate oxidation of sugars CO2 x2 4C 4C 6C 5C 4C CO2 COUNT THE ELECTRON CARRIERS pyruvate 3C 4C acetyl CoA 6C 4C NADH This happens twice for each glucose molecule 2C citrate reduction of electron carriers x2 4C FADH2 4C ATP 6C CO2 NADH 5C 4C CO2 NADH WHAT’S HAPPENED SO FAR? • We have fully oxidized glucose …C6H12O6 ...…CO2 & ended up with 4 ATP What’s the point? • Krebs cycle produces large quantities of electron carriers • NADH • FADH2 • Go to Electron Transport Chain What’s so important about electron carriers? ELECTRON CARRIERS = HYDROGEN CARRIERS H+ H+ + H+ H+ H + H + H H+ ADP + Pi ATP H+ ENERGY ACCOUNTING OF KREBS 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 VALUE OF KREBS CYCLE • If the yield is only 2 ATP, then how was the Krebs cycle a successful adaptation? • The value is in 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 What’s the point? The point is to make ATP! ATP AND HOW DO WE DO THAT? H+ • ATP Synthase H+ • Set up a H+ gradient • Allow H+ to flow through ATP synthase • Conformational change bonds Pi to ADP ADP + Pi ATP But… How do we get here? H+ H+ H+ H+ H+ H+ ADP + P ATP H+ We’re not done yet! Any questions so far?