Cellular Respiration Oxidation of Pyruvate Krebs Cycle 2005-2006

Glycolysis is only the start 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 2x 6C 3C glucose      pyruvate Can’t stop at pyruvate == not enough energy produced Pyruvate still has a lot of energy in it that has not been captured. It still has 3 carbons! There is still energy stored in those bonds. pyruvate       CO2 3C 1C 2005-2006

Cellular respiration 2005-2006

Recall: Structure of Mitochondria

Membrane-bound Enzymes 2005-2006

pyruvate    acetyl CoA + CO2 Oxidation of pyruvate Pyruvate enters mitochondria 3 step oxidation process releases 1 CO2 (count the carbons!) reduces NAD  NADH (stores energy) produces acetyl CoA Acetyl CoA enters Krebs cycle ( inside cristae) where does CO2 go? NAD NADH 3C 2C 1C pyruvate    acetyl CoA + CO2 [ 2x ] CO2 is fully oxidized carbon == can’t get any more energy out it CH4 is a fully reduced carbon == good fuel!!! Waiting to exhale? 2005-2006

Pyruvate oxidized to Acetyl CoA Onto Krebs reduction oxidation Release CO2 because completely oxidized…already released all energy it can release … no longer valuable to cell…. Because what’s the point? The Point is to make ATP!!! Yield = 2C sugar + CO2 + NADH Count sugars! 2005-2006

Pryruvic acid (pyruvate) crosses cristae MB Determine where the mbs are located (inner and outer) of the mitochondria on this picture! 2005-2006

Krebs cycle 1937 | 1953 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 billion years ago (glycolysis) free O2 2.7 billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic (oxygen) respiration (organelles) Hans Krebs 1900-1981

Count the carbons! x2 3C 2C 4C 6C 4C 6C 5C 4C 4C 4C pyruvate 3C 2C acetyl CoA citrate 4C 6C x2 4C 6C This happens twice for each glucose molecule oxidation of sugars CO2 5C 4C CO2 4C 4C

reduction of electron carriers Count the electron carriers! pyruvate 3C 2C acetyl CoA citrate 4C 6C NADH x2 4C 6C This happens twice for each glucose molecule CO2 reduction of electron carriers NADH 5C 4C CO2 FADH2 4C 4C NADH 2005-2006 ATP

Glucose is now fully oxidized! C6H12O6  CO2 & ended up with 4 ATP! What’s the Point? 2005-2006

What’s so important about NADH? NADH & FADH2 Krebs cycle produces large quantities of electron carriers NADH FADH2 stored energy! go to ETC What’s so important about NADH? 2005-2006

Energy accounting of Krebs cycle [ Energy accounting of Krebs cycle ] Net gain = 2 ATP = 8 NADH + 2 FADH2 4 NAD + 1 FAD 4 NADH + 1 FADH2 2x pyruvate          CO2 1 ADP 1 ATP 3C 3x 1C 2005-2006

So why the Krebs cycle? If the yield is only 2 ATP, then why? Because of value of NADH & FADH2 electron carriers reduced molecules store energy! to be used in the Electron Transport Chain 2005-2006

What’s the point? ATP The Point is to Make ATP! 2005-2006

Any Questions?? 2005-2006