Cellular Respiration Stage 2 & 3 Oxidation of Pyruvate Krebs Cycle AP 2006-2007 Biology 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 O 2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to pyruvate 3C 1C Cellular respiration 1
Oxidation of pyruvate Pyruvate enters mitochondrial matrix 2x pyruvate acetyl CoA + CO [ 2 3C 2C 1C ] 3 step oxidation process releases 2 (count the carbons!) reduces 2 NAD 2 (moves e - ) produces 2 acetyl CoA Acetyl CoA enters Krebs cycle NAD Where does the go? Exhale! Pyruvate oxidized to Acetyl CoA NAD + reduction Pyruvate C-C-C Coenzyme A oxidation Acetyl CoA C-C 2 x [ Yield = 2C sugar + NAD ] 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 O 2 2.7 billion years ago eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria) Hans Krebs 1900-1981 2
Count the electron carriers! pyruvate 3C oxaloacetate 2C acetyl CoA 6C citrate malate This happens twice for each glucose fumarate molecule reduction of electron carriers x2 6C 5C isocitrate α-ketoglutarate FADH 2 succinate Succinyl Co-A So we fully oxidized glucose C 6 H 12 O 6 & ended up with 4! What s the point? Electron Carriers = Hydrogen Carriers Krebs cycle produces large quantities of electron carriers FADH 2 go to Electron Transport Chain! ADP + P i H+ What s so important about electron carriers? 3
Energy accounting of Krebs cycle 4 NAD + 1 FAD 4 NAD 1 FADH 2 2x pyruvate 3C 3x 1C 1 ADP 1 Net gain = 2 = 8 NAD 2 FADH 2 Value of Krebs cycle? If the yield is only 2 then how was the Krebs cycle an adaptation? value of & FADH 2 electron carriers & H carriers reduced molecules move electrons reduced molecules move ions to be used in the Electron Transport Chain like $$ in the bank What s the point? The point is to make! AP 2006-2007 Biology 4
Cellular Respiration Stage 4 Electron Transport Chain Chemiosmosis AP 2006-2007 Biology accounting so far Glycolysis 2 Kreb s cycle 2 Life takes a lot of energy to run, need to extract more energy than 4! There s got to be a better way! I need a lot more! A working muscle recycles over 10 million s per second There is a better way! Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of to create gradient yields ~36 from 1 glucose! only in presence of O 2 (aerobic respiration) O 2 5
Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space fluid-filled space between membranes Oooooh! Form fits function! Electron Transport Chain Intermembrane space Inner mitochondrial membrane Q C dehydrogenase cytochrome bc complex Mitochondrial matrix cytochrome c oxidase complex Remember the Electron Carriers? Glycolysis glucose G3P Pyruvate Oxidation 2 8 2 FADH 2 Time to break open the piggybank! Krebs cycle 6
H e- + Electron Transport Chain NAD + + H e p e H Q FADH 2 NAD + dehydrogenase H e FAD Building proton gradient! cytochrome bc complex C e intermembrane space inner mitochondrial membrane 1 2 H 2 O cytochrome c oxidase complex mitochondrial matrix 2 + O 2 What powers the proton ( ) pumps? Stripping H from Electron Carriers Electron carriers pass electrons & to ETC H cleaved off & FADH 2 electrons stripped from H atoms (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC), flowing electrons = energy to do work transport proteins in membrane pump (protons) across inner membrane to intermembrane space + + + H+ TA-DA!! C Moving electrons Q e do the work! e e FADH 2 FAD ADP NAD + 2 1 + 2 O 2 H 2O + P i cytochrome cytochrome c dehydrogenase bc complex oxidase complex But what pulls the electrons down the ETC? O 2 H 2 O electrons flow downhill to O 2 oxidative phosphorylation 7
We did it! Set up a gradient Allow the protons to flow through synthase Synthesizes ADP + P i ADP + P i Chemiosmosis The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through synthase enzyme to build Chemiosmosis links the Electron Transport Chain to synthesis Pyruvate from cytoplasm Inner mitochondrial membrane Q Intermembrane space C Electron transport system 1. Electrons are harvested Acetyl-CoA and carried to the transport system. e - Krebs cycle e - FADH 2 e - 3. Oxygen joins with protons to form water. 2. Electrons provide energy to pump protons across the membrane. H 2 O 1 O 2 2 + 2 e - O 2 Mitochondrial matrix 4. Protons diffuse back in down their concentration gradient, driving the synthesis of. synthase 8
Cellular respiration 2 + 2 + ~36 9