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 H + flows through it conformational changes bond P i to ADP to make ATP set up a H + gradient allow the H + to flow down concentration gradient through ATP synthase ADP + P i ATP ADP ATP But How is the proton (H + ) gradient formed? + P H + H + H + H + H + H + H + H + H +
Got to wait until the sequel! Got the Energy? Ask Questions! H + H + H + H + H + H + H + H + ADP + P ATP 2006-2007 H +
Glycolysis: What to know! 1. What is the purpose of each step? 2. What type of reaction is happening? 3. What type of enzyme is used (NOT THE NAME OF THE ENZYME) 4. Energy distribution at each step. 5. Reactants and Products of each step
Glycolysis: Two major phases 1. investment phase energy (ATP) used up to split the molecule steps 1 through 5 2. pay-off phase energy molecules (ATP and NADH) are produced steps 6 through 10
Glycolysis: Step by Step Step 1: carbon 6 phosphorylated using ATP to prevent glucose from leaving the cell rxn type: phosphorylation enzyme: kinase energy: absorbed
Glycolysis: Step by Step Step 2: atoms of molecule are rearranged rxn type: isomerization enzyme: isomerase energy: equivalent
Glycolysis: Step by Step Step 3: carbon 1 phosphorylated to cause the molecule to be energetically unstable rxn type: phosphorylation enzyme: kinase energy: absorbed
Glycolysis: Step by Step Step 4: the unstable molecule is split into two molecules rxn type: cleavage enzyme: lyase energy: equivalent
Glycolysis: Step by Step Step 5: DHAP and G3P are isomers G3P is used in many other metabolic pathways rxn type: isomerization only glyceraldehyde-3- phosphate will continue to be used in glycolysis enzyme: isomerase energy: equivalent
Glycolysis: Step by Step Step 6: NADH (energy molecule) is created rxn type: redox phophorylation enzyme: dehydrogenase energy: released
NAD + / NADH NAD + nicotinamide adenine dinucleotide (oxidized form) NADH nicotinamide adenine dinucletide (reduced form)
Glycolysis: Step by Step Step 7: ADP phosphorylation to create ATP rxn type: substratelevel phosphorylation enzyme: kinase energy: released
Glycolysis: Step by Step Step 8: phosphate moved from carbon 3 to carbon 2 rxn type: isomerization enzyme: isomerase energy: equivalent
Glycolysis: Step by Step Step 9: water removed to set up next reaction rxn type: dehydration enzyme: lyase energy: released
Glycolysis: Step by Step Step 10: ADP phosphorylation to ATP rxn type: substratelevel phosphorylation enzyme: kinase
http://www.youtube.com/watch?v=bjsc QsVXKTY
Glycolysis Summary 1. glucose 2 pyruvate 2. net 2 ATP molecules produced 2 used; 4 generated 3. 2 NADH molecules produced
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) 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 Decarboxylation 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!
Oxidation Decarboxylation NAD + reduction Pyruvate C-C-C CO 2 Coenzyme A oxidation Acetyl CoA C-C Yield = 2C sugar + NADH + 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
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 + H + H + H + H + H + H+ H + H + What s so important about electron carriers?
Krebs Cycle Summary 1. two cycles of Krebs for EACH glucose molecule 2. acetyl-coa oxaloacetate (per cycle) 3. 4 CO 2 released 4. 6 NADH produced 5. 2 FADH 2 produced 6. 2 ATP produced
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 H + 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 H + gradient allow H + to flow through ATP synthase powers bonding of P i to ADP ADP + P H + H + H + H + H + H + H + H + ADP + P i ATP ATP H + 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 transport of electrons down ETC linked to pumping of H + to create H + 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 Ox-decarb and 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- + H + H + H + Building proton gradient! C H + intermembrane space inner mitochondrial membrane NADH e H Q FADH 2 NAD + NADH dehydrogenase H e FAD cytochrome bc complex e 2H + + O 2 1 2 H 2 O cytochrome c oxidase complex mitochondrial matrix What powers the proton (H + ) pumps?
In general: 1. 1 NADH 2.5 3 ATP molecules 2. 1 FADH2 1.5 2 ATP molecules 2005-2006
Stripping H from Electron Carriers Electron carriers pass electrons & H + to ETC H cleaved off NADH & FADH 2 electrons stripped from H atoms H + (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) flowing electrons = energy to do work transport proteins in membrane pump H + (protons) across inner membrane to intermembrane space TA-DA!! Moving electrons do the work! NADH H + H + H + H + Q e FADH 2 NAD + NADH dehydrogenase H + H + H + H + e FAD cytochrome bc complex C H + e 2H + + O 2 1 2 H 2 O cytochrome c oxidase complex ADP + P i ATP H + H + H + H + H+ 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 H + gradient Allow the protons to flow through ATP synthase Synthesizes ATP proton-motive force H + H + H + H + H + H + H + H + ADP + P i ATP ADP + P i Are we there yet? ATP H +
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!
Peter Mitchell 1961 1978 Proposed chemiosmotic hypothesis revolutionary idea at the time proton motive force 1920-1992
Pyruvate from cytoplasm Inner mitochondrial membrane H + Q H + 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 + H 2 O 1 O 2 2 + 2H + e - H + O 2 ATP Mitochondrial matrix 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. ATP ATP H + 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 (no NAD+!!!) ATP production ceases cells run out of energy and you die! H + NADH dehydrogenase H + FAD cytochrome bc complex H + e 2H + + O 2 1 2 H 2 O cytochrome c oxidase complex
NAD+ is important because it Is an important input to the Kreb Cycle Without NAD+, no NADH can be created and the Kreb Cycle will stop running
Q: Do you think glycolysis can still work? A: Yes, but why, if this process still needs NAD+? If there is no O 2 present, where does the NAD+ come from? From two processes
Anaerobic Metabolism Two processes of anaerobic metabolism: 1.lactic acid fermentation (humans) 2.alcohol fermentation (yeast) In the absence of O 2, cells still want to try to make as much energy as possible using only glycolysis.
1. Lactic Acid Fermentation
1. Lactic Acid Fermentation In the absence of O 2, lactate dehydrogenase converts pyruvate into lactic acid in humans. lactic acid (lactate) is a 3 carbon molecule NADH is converted back into NAD + for glycolysis to continue to occur. Once enough O 2 has returned to the cells, lactic acid is converted back into pyruvate.
2. Alcohol Fermentation
2. Alcohol Fermentation In the absence of O 2 : 1. pyruvate is decarboxylated (loss of CO 2 ) into acetaldehyde 2. alcohol dehydrogenase converts acetaldehyde into ethanol NADH is converted back into NAD+ for glycolysis to continue to occur. Ethanol will not be converted back to pyruvate even if O 2 concentration has increased due to loss of CO 2.
Anaerobic Fermentation Summary 1. lactic acid fermentation 1. pyruvate lactic acid 2. NADH NAD + 2. alcohol fermentation 1. pyruvate acetaldehyde ethanol 2. CO 2 released 3. NADH NAD +
What s the point? The point is to make ATP! ATP 2006-2007
Chapter 9. Cellular Respiration Other Metabolites & Control of Respiration 2005-2006
Cellular respiration 2005-2006
Beyond glucose: Other carbohydrates Glycolysis accepts a wide range of carbohydrates fuels polysaccharides glucose ex. starch, glycogen hydrolysis other 6C sugars glucose modified ex. galactose, fructose 2005-2006
Beyond glucose: Proteins Proteins amino acids hydrolysis waste H H amino group = waste product excreted as ammonia, urea, or uric acid N H C R O C OH glycolysis Krebs cycle carbon skeleton = enters glycolysis or Krebs cycle at different stages 2005-2006
Beyond glucose: Fats Fats glycerol & fatty acids hydrolysis glycerol (3C) PGAL glycolysis fatty acids 2C acetyl groups acetyl coa Krebs cycle glycerol fatty acids enters glycolysis as PGAL enter Krebs cycle as acetyl CoA 2005-2006
Carbohydrates vs. Fats Fat generates 2x ATP vs. carbohydrate more C in gram of fat more O in gram of carbohydrate so it s already partly oxidized fat carbohydrate 2005-2006
Metabolism Coordination of digestion & synthesis by regulating enzyme Digestion digestion of carbohydrates, fats & proteins all catabolized through same pathways enter at different points cell extracts energy from every source CO 2 2005-2006
Metabolism Coordination of digestion & synthesis by regulating enzyme Synthesis enough energy? build stuff! cell uses points in glycolysis & Krebs cycle as links to pathways for synthesis run the pathways backwards eat too much fuel, build fat pyruvate glucose Krebs cycle intermediaries amino acids Cells are versatile & thrifty acetyl CoA fatty acids 2005-2006
Control of Respiration Feedback Control 2005-2006
Feedback Inhibition Regulation & coordination of production production is self-limiting final product is inhibitor of earlier step allosteric inhibitor of earlier enzyme no unnecessary accumulation of product A B C D E F G X enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 6 allosteric inhibitor of enzyme 1 2005-2006
Respond to cell s needs Key points of control phosphofructokinase allosteric regulation of enzyme can t turn back step before splitting glucose AMP & ADP stimulate ATP inhibits citrate inhibits Why is this regulation important? Balancing act: availability of raw materials vs. energy demands vs. synthesis 2005-2006
A Metabolic economy Basic principles of supply & demand regulate metabolic economy balance the supply of raw materials with the products produced these molecules become feedback regulators they control enzymes at strategic points in glycolysis & Krebs cycle AMP, ADP, ATP regulation by final products & raw materials levels of intermediates compounds in the pathways regulation of earlier steps in pathways levels of other biomolecules in body regulates rate of siphoning off to synthesis pathways 2005-2006
It s a Balancing Act Balancing synthesis with availability of both energy & raw materials is essential for survival! do it well & you survive longer you survive longer & you have more offspring you have more offspring & you get to take over the world Acetyl CoA is central to both energy production & synthesis make ATP or store it as fat 2005-2006
Any Questions?? 2005-2006