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Chapter 9. Cellular Respiration Oxidation of Pyruvate Krebs Cycle AP Biology 2005-2006 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 oxidation of sugar to CO2 pyruvate → → → → → → CO2 AP Biology 3C 1C 2005-2006 Cellular respiration AP Biology 2005-2006 What’s the point? ATP The Point is to Make ATP! AP Biology 2005-2006 Oxidation of pyruvate Pyruvate enters mitochondria [ 2x pyruvate → → → acetyl CoA + CO2 3C 2C 1C NAD ] NADH 3 step oxidation process releases 1 CO2 (count the carbons!) reduces NAD → NADH (stores energy) produces acetyl CoA Acetyl CoA enters Krebs cycle AP Biology where does CO2 go? Waiting to exhale? 2005-2006 Pyruvate oxidized to Acetyl CoA reduction oxidation Yield = 2C sugar + CO2 + NADH AP Biology 2005-2006 Krebs cycle 1937 | 1953 aka Citric Acid Cycle in mitochondrial matrix 8 step pathway Hans Krebs 1900-1981 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 O2 →2.7 billion years ago (photosynthesis) AP Biology eukaryotes →1.5 billion years ago (aerobic respiration (organelles) 2005-2006 Count the carbons! pyruvate 3C 2C 6C 4C This happens twice for each glucose molecule AP Biology acetyl CoA citrate x2 4C 6C oxidation of sugars CO2 5C 4C 4C 4C CO2 2005-2006 Count the electron carriers! pyruvate 3C FADH2 AP Biology citrate x2 4C 4C acetyl CoA 6C 4C NADH This happens twice for each glucose molecule 2C 6C reduction of electron carriers 4C ATP 4C CO2 NADH 5C CO2 NADH 2005-2006 Whassup? So we fully oxidized glucose C6H12O6 ↓ CO2 & ended up with 4 ATP! AP Biology What’s the Point? 2005-2006 NADH & FADH2 Krebs cycle produces large quantities of electron carriers NADH FADH2 stored energy! go to ETC AP Biology What’s so important about NADH? 2005-2006 Energy accounting of Krebs cycle [ 4 NAD + 1 FAD 2x pyruvate → → → → → → → → → CO2 3C 3x 1C 1 ADP ] 4 NADH + 1 FADH2 1 ATP Net gain = 2 ATP = 8 NADH + 2 FADH2 AP Biology 2005-2006 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 AP Biology 2005-2006 What’s the point? ATP The Point is to Make ATP! AP Biology 2005-2006 Any Questions?? AP Biology 2005-2006