Cellular Respiration Harvesting Chemical Energy ATP 2006-2007
What s the point? The point is to make ATP! ATP 2006-2007
Harvesting stored energy Energy is stored in organic molecules carbohydrates, fats, proteins Heterotrophs eat these organic molecules food digest organic molecules to get raw materials for synthesis fuels for energy controlled release of energy burning fuels in a series of step-by-step enzyme-controlled reactions
respiration Harvesting stored energy Glucose is the model catabolism of glucose to produce ATP glucose + oxygen energy + water + carbon dioxide C 6 H 12 O 6 + 6O 2 ATP + 6H 2 O + 6CO 2 + heat COMBUSTION = making a lot of heat energy by burning fuels in one step fuel arbohydrates) O 2 CO 2 + H 2 O + heat RESPIRATION = making ATP (& some heat) by burning fuels in many small steps ATP glucose enzymes O 2 ATP CO 2 + H 2 O + ATP (+ heat)
How do we harvest energy from fuels? Digest large molecules into smaller ones break bonds & move electrons from one molecule to another as electrons move they carry energy with them that energy is stored in another bond, released as heat or harvested to make ATP loses e- gains e- oxidized reduced + + + e - e - oxidation redox e - reduction
How do we move electrons in biology? Moving electrons in living systems electrons cannot move alone in cells electrons move as part of H atom move H = move electrons loses e- gains e- oxidized reduced + + + H oxidation oxidation e p H reduction C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATP H e - reduction
Coupling oxidation & reduction REDOX reactions in respiration release energy as breakdown organic molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms C 6 H 12 O 6 CO 2 = the fuel has been oxidized electrons attracted to more electronegative atoms in biology, the most electronegative atom? O 2 H 2 O = oxygen has been reduced couple REDOX reactions & 2 use the released energy to synthesize ATP oxidation C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATP O reduction
Oxidation & reduction Oxidation adding O removing H loss of electrons releases energy exergonic Reduction removing O adding H gain of electrons stores energy endergonic oxidation C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATP reduction
Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around NAD + nicotinamide Vitamin B3 niacin O O P O O NAD + NADH (reduced) FAD +2 FADH 2 (reduced) H N + O C NH 2 + H reduction oxidation like $$ in the bank NADH O O P O O reducing power! H H N + O C NH 2 How efficient! Build once, use many ways phosphates O O P O O adenine O O P O O ribose sugar carries electrons as a reduced molecule
Overview of cellular respiration 4 metabolic stages Anaerobic respiration 1. Glycolysis respiration without O 2 in cytosol Aerobic respiration respiration using O 2 in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C 6 H 12 O 6 + 6O 2 ATP + 6H 2 O + 6CO 2 (+ heat)
What s the point? The point is to make ATP! ATP 2006-2007
And how do we do that? ATP synthase enzyme flows through it conformational changes bond P i to ADP to make ATP set up a gradient allow the to flow down concentration gradient through ATP synthase ADP + P i ATP ADP ATP But How is the proton ( ) gradient formed? + P
Got to wait until the sequel! Got the Energy? Ask Questions! ADP + P ATP 2006-2007
Cellular Respiration Stage 1, 2, & 3: Glycolysis Oxidation of Pyruvate Krebs Cycle 2006-2007
Overview 10 reactions Converts glucose (6C) to 2 pyruvate (3C) Produces: 4 ATP & 2 NADH Consumes: 2 ATP Net: 2 ATP & 2 NADH glucose C-C-C-C-C-C fructose-1,6bp P-C-C-C-C-C-C-P DHAP P-C-C-C 2P i G3P C-C-C-P 2H 2P i 2 2 pyruvate C-C-C ATP ADP 2 2 4 4 NAD + ADP ATP
Glycolysis is only the start Glycolysis glucose pyruvate 6C Pyruvate has more energy to yield 3 more C to strip off (to oxidize) 2x 3C if O 2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to CO 2 pyruvate CO 2 3C 1C
Cellular respiration
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 membrane cristae matrix What cells would have AP a lot Biology 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
Oxidation of pyruvate Pyruvate enters mitochondrial matrix [ ] 2x 3C pyruvate acetyl CoA + CO 2 2C 1C NAD 3 step oxidation process reduces 2 NAD 2 NADH (moves e - ) produces 2 acetyl CoA releases 2 CO 2 (count the carbons!) 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 1937 1953 aka Citric Acid Cycle in mitochondrial matrix 8 step pathway Hans Krebs each catalyzed by specific enzyme 1900-1981 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 4C 2C acetyl CoA 6C citrate This happens twice for each glucose molecule 4C 4C oxidation of sugars x2 6C 5C CO 2 4C 4C CO 2
Count the electron carriers! pyruvate NADH 3C 2C 4C 6C acetyl CoA citrate CO 2 NADH This happens twice for each glucose molecule 4C 4C reduction of electron carriers x2 6C 5C CO 2 NADH FADH 2 4C ATP 4C CO 2 NADH
So What? 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
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 How it works: 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 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 TA-DA!! Moving electrons do the work! 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 H+
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 proton-motive force ADP + P i ATP ADP + P i 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 So that s the point!
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 What is the final electron acceptor in Electron Transport Chain? O 2 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!
Anaerobic Cellular Respiration Some organisms thrive in environments with little or no oxygen Marshes, bogs, gut of animals, sewage treatment ponds No oxygen used= an aerobic Results in no more ATP, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis. End products such as ethanol and CO 2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)
Cellular respiration Summary! 2005-2006
Any Questions?? 2005-2006