Ch. 9 Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle 2006-2007
Glycolysis is only the start Glycolysis glucose pyruvate 6C Pyruvate has more energy to yield 3 more C to strip off (to oxidize) if O 2 is available, pyruvate enters mitochondria 2x 3C enzymes of Krebs cycle complete the full oxidation of sugar to CO 2 pyruvate CO 2 3C 1C
Cellular respiration 2 2 32
Mitochondria Structure Double membrane energy harvesting organelle smooth outer membrane highly folded inner membrane cristae intermembrane space fluid-filled space between membranes matrix inner fluid-filled space DNA, ribosomes enzymes free in matrix & membrane-bound outer intermembrane space inner membrane cristae membrane matrix What cells would have a lot of mitochondria? mitochondrial DNA
Mitochondria Function Dividing mitochondria Who else divides like that? bacteria! Oooooh! Form fits function! Membrane-bound proteins Enzymes & permeases What does this tell us about the evolution of eukaryotes? Endosymbiosis! Advantage of highly folded inner membrane? More surface area for membranebound enzymes & permeases
xidation of Pyruvate 3C C C C Remember, this happens twice,once for each Pyruvate! Acetyl Group C C C Loss of CO 2 NAD+ e- & H+ Hydride Where Ion donated does the Carbon go? + Coenzyme A (CoA) Exhale! 2 = 2 CO 2 = 2 NADH = 2 Acetyl CoA Acetyl-CoA C C To the Krebs Cycle!
Oxidation of pyruvate Pyruvate enters mitochondrial matrix [ ] 2x 3C pyruvate acetyl CoA + CO 2 2C 1C NAD 3 step oxidation process releases 2 CO 2 (count the carbons!) reduces 2 NAD 2 NADH (moves e - ) produces 2 acetyl CoA Acetyl CoA enters Krebs cycle Where does the CO 2 go? Exhale!
Pyruvate oxidized to Acetyl CoA NAD + reduction Pyruvate C-C-C CO 2 Coenzyme A oxidation Acetyl CoA C-C Yield = 2C sugar + NAD CO 2 2 x [ ]
Krebs cycle 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 (photosynthesis) eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria)
Count the carbons! pyruvate 3C 2C acetyl CoA 4C 6C citrate This happens twice for each glucose molecule 4C 4C oxidation of sugars x2 6C 5C CO 2 4C 4C CO 2
Now, count the electron carriers! pyruvate 3C 2C acetyl CoA NADH 4C 6C citrate This happens twice for each pyruvate molecule 4C 4C reduction of electron carriers x2 6C 5C CO 2 NADH FADH 2 4C ATP 4C CO 2 NADH
Whassup? So we fully oxidized glucose C 6 H 12 O 6 CO 2 & ended up with 4 ATP! What s the point?
Electron Carriers = Hydrogen Carriers Krebs cycle produces large quantities of electron carriers NADH FADH 2 go to Electron Transport Chain! ADP + P i ATP H+ What s so important about electron carriers?
Energy accounting of Krebs cycle 4 NAD + 1 FAD 4 NAD 1 FADH 2 2x pyruvate CO 2 3C 1 ADP 1 ATP 3x 1C Net gain = 2 ATP = 8 NAD 2 FADH 2
Value of Krebs cycle? If the yield is only 2 ATP then how was the Krebs cycle an adaptation? value of NADH & 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 ATP! ATP 2006-2007
And how do we do that? ATP synthase set up a gradient allow to flow through ATP synthase powers bonding of P i to ADP ADP + P ADP + P i ATP ATP But Have we done that yet?
NO! The final chapter to my story is next! Any Questions? 2006-2007
Ch. 9 Cellular Respiration Stage 4: Electron Transport Chain 2006-2007
Cellular respiration
What s the point? The point is to make ATP! ATP 2006-2007
ATP accounting so far Glycolysis 2 ATP Kreb s cycle 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! There s got to be a better way! I need a lot more ATP! A working muscle recycles over 10 million ATPs 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 ATP from 1 glucose! only in presence of O 2 (aerobic respiration) That sounds more like it! O 2
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 C Q NADH dehydrogenase Mitochondrial matrix cytochrome bc complex cytochrome c oxidase complex
Remember the Electron Carriers? Glycolysis glucose G3P Krebs cycle 2 NADH 8 NADH 2 FADH 2 Time to break open the piggybank!
Electron Transport Chain NADH NAD + + H e p H e- + Building proton gradient! C intermembrane space inner mitochondrial membrane http://vcell.ndsu.edu/a nimations/etc/movieflash.htm NADH e H Q FADH 2 NAD + NADH dehydrogenase H e FAD cytochrome bc complex e 2 + O 2 1 2 H 2 O cytochrome c oxidase complex mitochondrial matrix What powers the proton ( ) pumps?
Stripping H from Electron Carriers Electron carriers pass electrons & to ETC H cleaved off NADH & 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+ NADH Q e FADH 2 NAD + NADH dehydrogenase e FAD cytochrome bc complex C e 2 + O 2 1 2 H 2 O cytochrome c oxidase complex ADP + P i ATP
Chemiosmosis powers the pump! The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP TA-DA!! Moving electrons do the work! NADH e Q FADH 2 NAD + NADH dehydrogenase e FAD cytochrome bc complex C 1 2 e 2 + O 2 H 2 O cytochrome c oxidase complex O- ADP + P i O- O- ATP P P P P P H H+ + O-
But what pulls the electrons down the ETC? H 2 O O 2 electrons flow downhill to O 2 oxidative phosphorylation
Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy make ATP instead of fire!
We did it! Set up a gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + P i ATP ADP + P i proton-motive force Are we there yet? ATP
Chemiosmosis The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis http://www.youtube.com/watch?v=3y1do4nnaky So that s the point!
Peter Mitchell 1961 1978 Proposed chemiosmotic hypothesis revolutionary idea at the time proton motive force 1920-1992
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. NADH e - Krebs cycle NADH CO 2 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 ATP Mitochondrial matrix 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. ATP ATP ATP synthase
Cellular respiration 2 ATP 2 ATP ~36 ATP + +
Summary of cellular respiration C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ~40 ATP Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe?
Taking it beyond C What is the final electron acceptor in Q e Electron Transport Chain? e FADH 2 O 2 NADH NAD + So what happens if O 2 unavailable? ETC backs up nothing to pull electrons down chain NADH & FADH 2 can t unload H ATP production ceases cells run out of energy and you die! NADH dehydrogenase FAD cytochrome bc complex e 2 + O 2 1 2 H 2 O cytochrome c oxidase complex
What happens when you run out of Oxygen! http://www.youtube.com/watch?v=stxlo1w3 Gvg&feature=related
What s the point? The point is to make ATP! ATP 2006-2007