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Transcript
Making energy! ATP The point is to make ATP! Enduring Understandings II. A. Growth, reproduction and maintenance of the organization of living systems require free energy and matter. 1. 2. IV. All living systems require a constant input of free energy. Organisms capture and store free energy for use in biological processes. A. Interactions within biological systems lead to complex properties. 2. The structure and function of subcellular components, and their interactions, provide essential cellular processes. Discussion What is the fundamental coupled reaction that makes up cellular respiration? The energy needs of life Organisms are endergonic systems Humans require ~2000 kilocalories per day What do we need energy for? synthesis building biomolecules reproduction movement active transport temperature regulation Where do we get the energy from? Work of life is done by energy coupling use exergonic (catabolic) reactions to fuel endergonic (anabolic) reactions digestion + synthesis + + energy + energy Recall ATP… ADP ATP O– O– O – –O P –O O– P –O O– P O– O O O O– –O P O – + O 7.3 energy ATP ADP releases energy ∆G = -7.3 kcal/mole Fuel other reactions Phosphorylation released Pi can transfer to other molecules destabilizing the other molecules enzyme that phosphorylates = “kinase” An example of Phosphorylation: dehydration synthesis Building polymers from monomers H H C C OHHO need to destabilize the monomers, H2O doesn’t just come off on its own phosphorylate! H C OH H C OH H C + H C HO synthesis +4.2 kcal/mol “kinase” + ATP + P H C HO enzyme -7.3 kcal/mol -3.1 kcal/mol enzyme H H C C O H C + + H2O ADP P H H C C O + Pi Another example of Phosphorylation… The first steps of cellular respiration starting the breakdown of glucose requires some ATP investment “Substrate-level phosphorylation” glucose C-C-C-C-C-C hexokinase phosphofructokinase P 2 ATP C C 2 ADP fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P H C P activation energy H+ H+ Our end goal… H+ ATP Synthase, enzyme H+ H+ H+ H+ H+ channel in mitochondrial membrane rotor permeable to H+ H+ flow down concentration gradient rod catalytic head flow like water over water wheel flowing H+ cause change in shape of ATP synthase enzyme powers bonding of Pi to ADP: ADP + Pi ATP ADP + P ATP H+ Cellular Respiration Harvesting Chemical Energy ATP Harvesting stored energy Energy is stored in organic molecules carbohydrates, fats, proteins Heterotrophs eat these organic molecules food Catabolize/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 Overview of cellular respiration 4 metabolic stages Anaerobic respiration 1. Glycolysis respiration without O2 in cytosol Aerobic respiration respiration using O2 in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain ->ATP Synthase C6H12O6 + 6O2 ATP + 6H2O + 6CO2 (+ heat) Cellular Respiration Stage 1: Glycolysis Glycolysis Breaking down glucose “glyco – lysis” (splitting sugar) glucose pyruvate 2x 3C 6C ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to ATP still is starting point for ALL cellular respiration but it’s inefficient generate only 2 ATP for every 1 glucose Anaerobic, occurs in cytosol That’s not enough ATP for me! Discussion Why does it make evolutionary sense that the earliest of the energy-releasing processes is glycolysis, which takes place in the cytosol? Evolutionary perspective glucose C-C-C-C-C-C Overview 10 reactions convert glucose (6C) to 2 pyruvate (3C) produces: +4 ATP & +2 NADH consumes: -2 ATP enzyme 2 ATP enzyme 2 ADP fructose-1,6bP P-C-C-C-C-C-C-P enzyme enzyme enzyme DHAP P-C-C-C net yield: 2 pyruvate, 2 ATP & 2 NADH DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate G3P C-C-C-P 2H 2Pi enzyme 2 NAD+ 2 enzyme 2Pi 4 ADP enzyme pyruvate C-C-C 4 ATP Glycolysis summary endergonic invest some ATP ENERGY INVESTMENT -2 ATP ENERGY PAYOFF G3P C-C-C-P 4 ATP exergonic harvest a little ATP & a little NADH like $$ in the bank NET YIELD net yield 2 ATP 2 NADH Is that all there is? Not a lot of energy… for 1 billon years+ this is how life on Earth survived no O2 = slow growth, slow reproduction only harvest 3.5% of energy stored in glucose more carbons to strip off = more energy to harvest O2 O2 O2 O2 O2 glucose pyruvate 2x 3C 6C But can’t stop there! G3P DHAP NAD+ raw materials products Pi + NADH NAD NADH Pi 1,3-BPG NAD+ Pi + NADH NAD 1,3-BPG NADH 7 ADP Glycolysis 6 Pi ADP ATP ATP 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) glucose + 2ADP + 2Pi + 2 NAD+ 2 pyruvate + 2ATP + 2NADH 8 Going to run out of NAD+ 9 H2O without regenerating NAD+, energy production would stop! Phosphoenolpyruvate (PEP) another molecule must accept e-ADP 10 from NADH ATP so NAD+ is freed up for another round Pyruvate H2O Phosphoenolpyruvate (PEP) ADP ATP Pyruvate How is NADH recycled to NAD+? Another molecule must accept H from NADH H2O O2 recycle NADH with oxygen without oxygen aerobic respiration anaerobic respiration “fermentation” pyruvate NAD+ NADH acetyl-CoA CO2 NADH NAD+ lactate acetaldehyde NADH NAD+ lactic acid fermentation which path you use depends on who you are… Krebs cycle ethanol alcohol fermentation Pyruvate is a branching point Pyruvate O2 O2 fermentation anaerobic respiration mitochondria Krebs cycle aerobic respiration Fermentation (anaerobic) Yeast, fungi pyruvate ethanol + CO2 3C NADH 2C NAD+ beer, wine, bread 1C back to glycolysis Animals, some bacteria pyruvate lactic acid 3C NADH 3C NAD+back to glycolysis cheese, anaerobic exercise (no O2) Alcohol Fermentation pyruvate ethanol + CO2 3C NADH 2C 1C NAD+ back to glycolysis Dead end process at ~12% ethanol, kills yeast can’t reverse the reaction Bacteria Fungi recycle NADH Lactic Acid Fermentation pyruvate lactic acid 3C NADH O2 3C NAD+ back to glycolysis Reversible process once O2 is available, lactate is converted back to pyruvate by the liver Why would this be reversible but not alcoholic ferm.? (Hint: C) animals bacteria recycle NADH Discussion Knowing what you do about glucose catabolism so far, how can we use bacteria and yeast to… Make bread rise? Make alcoholic drinks? If you want to make bread or an alcoholic drink, what should the bacteria or yeast environment contain? What should it not contain? Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle 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 prokaryotic DNA (mDNA), ribosomes enzymes intermembrane free in matrix & membrane-bound space What cells would have a lot of mitochondria? outer membrane inner membrane cristae matrix mitochondrial DNA Mitochondria – Function Oooooh! Form fits function! Membrane-bound proteins: Enzymes & permeases (membrane transport proteins) Advantage of highly folded inner membrane? More surface area for membrane-bound enzymes & permeases Discussion Thinking of the human body, which kinds of cells would you expect would have more mitochondria? Which would you expect would have less? (If you’ve learned this in anatomy, be nice, give your partner a chance to try their hand at it first :P) 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 O2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to CO2 pyruvate CO2 3C 1C Cellular respiration Oxidation of pyruvate Pyruvate enters mitochondrial matrix [ 2x pyruvate acetyl CoA + CO2 3C 2C 1C NAD Pyruvate is oxidized releases 2 CO2 (count the carbons!) reduces 2 NAD 2 NADH (moves e-) produces 2 (two-carbon) acetyl CoA Acetyl CoA enters Krebs cycle ] Pyruvate oxidized to Acetyl CoA reduction NAD+ Pyruvate C-C-C [ Coenzyme A CO2 Acetyl CoA C-C oxidation 2 x Yield = 2C sugar + NADH + CO2 ] Krebs cycle 1937 | 1953 aka Citric Acid Cycle in mitochondrial matrix 8 step pathway each catalyzed by specific enzyme Hans Krebs 1900-1981 step-wise catabolism of 6C citrate molecule Evolved later than glycolysis Evolutionarily… bacteria 3.5 billion years ago (glycolysis) free O2 2.7 billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria) Count the carbons! pyruvate 3C 2C 6C 4C This happens twice for each glucose molecule, because glycolysis produced two pyruvates 4C acetyl CoA citrate oxidation of sugars CO2 x2 4C 4C 6C 5C 4C CO2 Count the electron carriers! pyruvate 3C 2C 6C 4C NADH 4C 4C acetyl CoA citrate reduction of electron carriers x2 FADH2 4C ATP CO2 NADH 6C CO2 NADH 5C 4C CO2 NADH What happened? So we fully oxidized glucose C6H12O6 CO2 & ended up with 4 ATP! What’s the point? :/ http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html Electron Carriers = Hydrogen Carriers H+ Krebs cycle produces large quantities of electron carriers NADH FADH2 go to Electron Transport Chain! H+ H+ H+ + H+ H H+ H+ ADP + Pi ATP H+ Discussion Krebs Cycle and Glycolysis have given us energy carriers NADH, FADH2… …which will go to the electron transport chain… …where ATP synthase is located… PREDICT… how will we be able to use NADH and FADH2 to make ATP?? 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 Cellular Respiration Stage 4: Electron Transport Chain Cellular respiration 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 O2 (aerobic respiration) That sounds more like it! O2 Remember: Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins Matrix space within the inner membrane intermembrane space fluid-filled space between membranes Electron Transport Chain Intermembrane space Outer mitochondrial membrane Inner mitochondrial membrane C Q NADH dehydrogenase cytochrome bc complex Mitochondrial matrix cytochrome c oxidase complex Remember the Electron Carriers? Glycolysis glucose Krebs cycle G3P 2 NADH Time to break open the piggybank! 8 NADH 2 FADH2 Electron Transport Chain Building proton gradient! NADH NAD+ + H e p intermembrane space H+ H+ H e- + H+ H+ C e– Q e– NADH H FADH2 NAD+ NADH dehydrogenase inner mitochondrial membrane e– H FAD 2H+ + cytochrome bc complex 1 2 O2 H2O cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps?… Stripping H from Electron Carriers Electron carriers pass electrons to ETC electrons stripped from H atoms 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 H+ + H H+ TA-DA!! Moving electrons do the work! + H H+ + H H+ H+ + H+ H+ H + H+ H H+ C e– NADH Q e– FADH2 FAD NAD+ NADH dehydrogenase e– 2H+ cytochrome bc complex + 1 2 O2 H2O cytochrome c oxidase complex ADP + Pi ATP H+ But what “pulls” the electrons down the ETC? H 2O O2 electrons flow downhill to O2 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 Taking it beyond… What is the final H+ H+ H+ C Q e– FADH2 FAD electron acceptor in e NADH 2H + NAD Electron Transport O2 Chain? So what happens if O2 unavailable? ETC backs up e– – + + NADH dehydrogenase cytochrome bc complex 1 2 O2 H2O cytochrome c oxidase complex nothing to pull electrons down chain NADH & FADH2 can’t unload H ATP production ceases cells run out of energy and you die! Pyruvate from cytoplasm Inner + mitochondrial H membrane H+ Intermembrane space Electron transport C system Q NADH Acetyl-CoA 1. Electrons are harvested and carried to the transport system. NADH Krebs cycle e- e- FADH2 e- 2. Electrons provide energy to pump protons across the membrane. e- H2O 3. Oxygen joins with protons to form water. 1 O 2 +2 2H+ O2 H+ CO2 ATP Mitochondrial matrix H+ ATP ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ ATP synthase http://www.qcc.cuny.edu/biologicalsciences/Faculty/UGolebiewska/respiration.html ://www.youtube.com/watch?v=FFBr3ANCkb4 Cellular respiration 2 ATP + 2 ATP + ~36 ATP Discussion C6H12O6 + 6O2 6CO2 + 6H2O + ~40 ATP Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? http://www.youtube.com/watch?v=FFBr3AN Ckb4 Comparison of Chemiosmosis in Chloroplasts and Mitochondria ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP generates O2 use electron carrier NADPH ETC of Respiration Mitochondria transfer chemical energy from food molecules into chemical energy of ATP use electron carrier NADH generates H2O Cellular Respiration Other Metabolites & Control of Respiration Cellular respiration Other metabolites Cellular respiration is sequential. We can enter at multiple points along the pathway, if we can produce the molecule that usually belongs there some other way. We don’t HAVE to start with pure glucose! Beyond glucose: Other carbohydrates Glycolysis accepts a wide range of carbohydrates fuels polysaccharides glucose hydrolysis ex. starch, glycogen other 6C sugars glucose modified ex. galactose, fructose Beyond glucose: Fats fats glycerol + fatty acids hydrolysis glycerol (3C) G3P glycolysis fatty acids 2C acetyl acetyl Krebs groups coA cycle 3C glycerol enters glycolysis as G3P 2C fatty acids enter Krebs cycle as acetyl CoA Carbohydrates vs. Fats Fat generates 2x ATP vs. carbohydrate more C in gram of fat more energy releasing bonds more O in gram of carbohydrate That’s why it takes so much work to lose a pound a fat! already partly oxidized less energy to release carbohydrate fat Discussion Why would an organism ever convert acetyl CoA to fat instead of putting it through the Krebs Cycle and ETC? Krebs + ETC = ATP! ATP powers everything! What gives? Only 2C, clearly not a lot of energy this way, cells try to avoid it Beyond glucose: Proteins proteins amino acids hydrolysis waste H O H | || N —C— C—OH | H R amino group = waste product excreted as ammonia, urea, or uric acid glycolysis Krebs cycle 2C sugar = carbon skeleton = enters glycolysis or Krebs cycle at different stages Metabolism Digestion digestion of carbohydrates, fats & proteins all catabolized through same pathways enter at different points cell extracts energy from every source Cells are versatile & CO2 selfish! Metabolism Synthesis enough energy? build stuff! cell uses points in glycolysis & Krebs cycle as links to pathways for synthesis run pathways “backwards” have extra fuel, build fat! pyruvate glucose Krebs cycle intermediaries acetyl CoA amino acids fatty acids Cells are versatile & thrifty! Metabolic Rate Metabolic Rate Metabolic rate is the amount of energy required by an organism. Usually measured in units of energy per body mass per time (such as J/g/hr), or simply in energy per time (such as mm O2/day). Metabolic Rate Think of examples of animals of all sizes, and then hypothesize: who do you think probably has a higher metabolic rate (kcal/g/day), smaller organisms, larger ones, or no relationship? (Hint: it takes energy to maintain body temperature) Metabolic Rate Living things must expend energy to maintain the right body temperature for these enzymes to function Metabolic Rate Metabolic Rate Relationship exists between thermoregulation and metabolic rate Endotherms (mammals, birds) = Temperature regulation mostly thanks to internal processes: heat lost during routine metabolic processes Ectotherms (all other animals) = Body temperature regulation mostly thanks to external environment: very little heat generated by normal metabolism Discussion Predict: Sketch a graph with two lines: one for endotherms, one for ecotherms. X-Axis: Ambient (environmental) temperature Y-Axis: Rate of oxygen consumption Generating Heat Oxidative phosphorylation can be decoupled from the ETC Decoupling protein can redirect protons back across the membrane No ATP formed Energy dissipated as heat instead