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Chapter 9.2 Cellular Respiration: Pyruvate Oxidation & Citric Acid Cycle OVERVIEW OF GLYCOLYSIS 1 2 3 6-carbon glucose (Starting material) 2 ATP P P 6-carbon sugar diphosphate P P 6-carbon sugar diphosphate P P 3-carbon sugar 3-carbon sugar phosphate phosphate P 3-carbon sugar 3-carbon sugar phosphate phosphate NADH 2 ATP reactions. Glycolysis begins with the addition of energy. Two high-energy phosphates from two molecules of ATP are added to the six-carbon molecule glucose, producing a sixcarbon molecule with two phosphates. NADH 2 ATP 3-carbon pyruvate Priming reactions. Priming P 3-carbon pyruvate Cleavage reactions. Then, the Energy-harvesting reactions. six-carbon molecule with two phosphates is split in two, forming two three-carbon sugar phosphates. Finally, in a series of reactions, each of the two three-carbon sugar phosphates is converted to pyruvate. In the process, an energy-rich hydrogen is harvested as NADH, and two ATP molecules are formed. Glycolysis is only the start Glycolysis glucose pyruvate 6C 2x 3C but pyruvate has more energy to yield! 3 more C to strip off (to oxidize) if O2 is not available, pyruvate is reduced to regenerate NAD+ (meaning that NADH is oxidized to NAD+) Glycolysis is only the start Glycolysis glucose pyruvate 6C 2x 3C but 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 oxidation of sugar to CO2 pyruvate CO2 3C 1C Cellular Respiration Oxidation of Pyruvate Pyruvate enters mitochondria 2x [ pyruvate acetyl CoA + CO2 3C 2C NAD Waiting to exhale? 1C ] NADH 3 step oxidation process (on next slide) releases 1 CO2 (count the carbons!) reduces NAD NADH (stores energy—endergonic) 2C combines with CoA, producing acetyl CoA Acetyl CoA enters Krebs cycle where does CO2 go? Pyruvate oxidized to Acetyl CoA reduction x2 oxidation Yield = 2C compound + CO2 + NADH x2 Krebs cycle a.k.a. Citric Acid Cycle in mitochondrial matrix 8 step pathway each catalyzed by specific enzyme Hans Krebs 1900-1981 step-wise catabolism of 6C citrate molecule Evolved AFTER 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 respiration) Count the carbons! pyruvate 3C 2C acetyl CoA 6C 4C citrate x2 4C This happens twice for each glucose molecule! 6C oxidation of sugars CO2 5C 4C 4C 4C CO2 Count the electron carriers! pyruvate 3C 2C acetyl CoA 6C 4C NADH x2 4C 4C citrate 6C reduction of electron carriers ADP FADH2 4C ATP This happens twice for each glucose molecule! 4C CO2 NADH 5C CO2 NADH So we fully oxidized glucose C6H12O6 CO2 & ended up with a net gain of 4 ATP! What Is 4 ATP was all thewe point? get? NADH & FADH2 Krebs cycle produces large quantities of electron carriers NADH FADH2 stored energy! they go to ETC What’s so important about NADH and FADH2? Energy stored from Pyruvate Oxidation and Krebs Cycle 4 NAD + 1 FAD 2x 4 NADH + 1 FADH2 pyruvate CO2 3C 3x 1C 1 ADP Stored energy? What good is that? 1 ATP Net gain = 2 ATP = 8 NADH = 2 FADH2 So why the Krebs cycle? If the yield is only 2 ATP, then why? value of NADH & FADH2 electron carriers reduced molecules store energy! to be used in the Electron Transport Chain Ohhhh! I see. We just are slowly releasing the chemical energy from the bonds of glucose! Not so bad, right? RIGHT?!? Cellular Respiration What’s the point? ATP The Point is to Make ATP! Any Questions??