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Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle AP Biology 2006-2007 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) u if O2 is available, pyruvate enters mitochondria u enzymes of Krebs cycle complete the full oxidation of sugar to CO2 u pyruvate → → → → → → CO2 AP Biology 3C 1C Cellular respiration AP Biology Mitochondria — Structure § Double membrane energy harvesting organelle u u smooth outer membrane highly folded inner membrane § ________________ u ____________________________ § fluid-filled space between membranes u ____________________________ § inner fluid-filled space u u mitochondrial DNA, ribosomes enzymes § free in matrix & What cells would have AP Biology a lot of mitochondria? outer intermembrane membrane-bound membrane inner space membrane cristae matrix mitochondrial DNA Mitochondria – Function Oooooh! Form fits function! Dividing mitochondria Membrane-bound proteins Who else divides like that? Enzymes & permeases What does this tell us about the evolution of eukaryotes? __________________________ AP Biology Advantage of highly folded inner membrane? ____________________________ ____________________________ Oxidation of pyruvate § Pyruvate enters mitochondrial matrix [ 2x pyruvate → → → acetyl CoA + CO2 3C 2C 1C NAD ] Where does the CO2 go? Exhale! 3 step oxidation process u releases _______ (count the carbons!) u reduces _______________ (moves e-) u produces __________________ u § Acetyl CoA enters ________________ AP Biology Pyruvate oxidized to Acetyl CoA reduction NAD+ Pyruvate C-C-C [ CO2 Coenzyme A oxidation Acetyl CoA C-C 2 x Yield = 2C sugar + NADH + CO2 AP Biology ] Krebs cycle 1937 | 1953 § aka Citric Acid Cycle in _________________________ u 8 step pathway u § each catalyzed by specific enzyme Hans Krebs 1900-1981 § step-wise catabolism of 6C citrate molecule § Evolved later than glycolysis u 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 AP Biology respiration = organelles → mitochondria) Count the carbons! pyruvate 3C 2C 6C 4C This happens twice for each glucose molecule AP Biology 4C acetyl CoA citrate oxidation of sugars CO2 x2 4C 4C 6C 5C 4C CO2 Count the electron carriers! pyruvate 3C FADH2 AP Biology 6C 4C NADH This happens twice for each glucose molecule 2C 4C 4C acetyl CoA citrate __________ __________ __________ x2 4C ATP CO2 NADH 6C CO2 NADH 5C 4C CO2 NADH Whassup? So we fully oxidized glucose C6H12O6 ↓ CO2 & ended up with 4 ATP! AP Biology What’s the point? Electron Carriers = Hydrogen Carriers H+ § Krebs cycle produces large quantities of _______________ ____________ u ____________ u go to Electron Transport Chain! u AP Biology What’s so important about electron carriers? 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 AP Biology Value of Krebs cycle? § If the yield is only 2 ATP then how was the Krebs cycle an adaptation? u __________________________________ § ____________________________________ w __________________________________ w __________________________________ § ____________________________________ like $$ in the bank AP Biology What’s the point? The point is to make ATP! ATP AP Biology 2006-2007 H+ And how do we do that? H+ H+ H+ H+ H+ H+ H+ § ATP synthase set up a H+ gradient u allow H+ to flow through ATP synthase u powers bonding of Pi to ADP u ADP + P ADP + Pi → ATP ATP H+ AP Biology But… Have we done that yet? NO! The final chapter to my story is next! Any Questions? AP Biology 2006-2007