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Cellular Respiration What is cellular respiration? Why does it occur? Where does it occur? What are the steps of the process? What are the alternatives? This presentation borrows more heavily than most from the text illustrations. I hope that is useful here. Refer to chapters 6 and 8 in text. http://themedicalbiochemistrypage.org/tca-cyclereactions.jpg This is the process of cellular respiration. ←glucose ATP↑ http://erkki.kennesaw.edu/schem229/glycolysis2.jpg http://www.cellml.org/examples/images/oxidative_phosphorylation_2001/conventional_rendering.gif ATP: Adenosine TriPhosphate, the energy currency of the cell. Energy is stored in bonds. The most common source of energy for your enzymatic reactions (anabolism and catabolism) comes from the energy stored in this bond ….. From where comes the energy to recharge this ‘battery’ after it has been spent? (When this bond is broken ATP becomes ADP.) Energy is captured in chemical bonds (forming carbohydrates) through photosynthesis (more later!), and respiration is about getting it back out. Cell respiration is the controlled release of energy from organic compounds in cells to form ATP. http://www.freewebs.com/rumputrampai98/food.jpg From the food you eat! (Or the food you make if you are an autotroph, which you aren’t.) How much energy is there in glucose? C6H12O6 + 6O2 ->->->-> 6CO2 + 6H2O A Mole of glucose (180g) with 134 L of O2 (at STP) yields about 686 kilocalories (C)… But releasing it all at once, like a bonfire, would be of little use. (compare to a power plant) Organisms have a multipart process to harvest this energy in a useful manner, starting with glycolysis… Glycolysis “breaking glucose” note: - starting with glucose - investment of 2 ATPs to start process - splitting of F1,6BP (↓) into two 3C molecules ↑ where this happens Glycolysis (cont.) note - this is shown happening twice (once per G3P) - recovery of ATP (4 total, 2 net) by substrate-level phosphorylation - generation of NADH↓ nicotinamide adenine dinucleotide (2 total) (redox reactions) - end product is 2 pyruvates link reaction, aka bridge reactions (Mader calls this the preparatory reaction) getting into the mitochondrion note: - 2 per glucose - first CO2 coming off (decarboxylation) twice - another NADH made (2 of them per glucose) - product:(2) acetyl Co(enzyme)A Krebs Cycle /TCA/ Citric Acid Cycle note: - first product is citric acid (hence the name) - the balance of carbons: C2+C4 → C6 → C5+CO2 → C4+CO2 (two more CO2 off, and 4C oxaloacetate restored.) - 3 more NADH generated per round - 1 FADH2 generated [flavin adenine dinucleotide: not a dinucleotide] - 1 ATP made by substrate level phosphorylation - 2 rounds per glucose molecule RECAP Glucose is gone. 4 net ATP made per glucose 2 FADH2 10 NADH… a little bit of usable energy, and a bunch of “electron carriers” note: - electrons from NADH and FADH2 passed from carrier to carrier in a series of redox reactions. - H+ pumped into intermembrane space, making an electrochemical gradient. - oxygen finally receives electrons, and ties up H+ in matrix. - proton-motive force: protons flood through ATP synthase complex, generating ATP from ADP + Pi: This is an aerobic process. FADH2 dumps e- here→ electron transport chain, chemiosmosis, and ATP synthase NB ↑ oxidative phosphorylation ↑ Energy ledger: about 38 ATP per glucose -0 to 2 ATP per link? (NADH can’t cross…) What does this mean↑ “ + about” 34 ATP? (In actuality, total is closer to 30…) The text says your mitochondria produce about your body’s weight worth of ATP daily (p.143)No wonder cyanide (which blocks cytochromes) kills so fast! Draw and annotate a diagram showing the structure of a mitochondrion as seen in electron micrographs. note: - importance of extensive inner membranes (cristae) - role of narrow space between inner and outer membranes - Krebs cycle enzymes in matrix - electron tomography of mitochondrion https://www.youtube.com/watch?v=y6AvmNpHkJ0 Note that the reactions of aerobic respiration also occur in the membranes of prokaryotes! So, what if there is no oxygen to accept that electron at the end of the electron transport chain? No O2 receptor →(“means”) no electron transport chain → no oxidation of electron carriers (NADH, FADH2)→ no free receptors for e- in Krebs cycle → backup through link reactions → no energy from glucose breakdown. No O2 means no energy from glucose. Or does it? Fermentation Many organisms are able to get some energy/ATP from glucose with little or no oxygen. These allow a bit of ATP to be recharged in the absence of oxygen alcohol fermentation note: - Oxidizes NADH from glycolysis in making a waste product (ethanol). - Also generates CO2 (makes bread rise). -Occurs in yeast and some bacteria, when little oxygen is present. - Net gain 2 ATP per glucose. → http://fig.cox.miami.edu/~cmallery/150/makeatp/c8.9x18a.alcohol.jpg Alcohol distillation: Alcohol is toxic to the yeast at about 10%. Alcohol’s boiling point is lower than that of water. Are you surprised? (Alcohol is non-polar….) Fermented mash is filtered and boiled. The alcohol vapor, coming off first, is condensed and collected. The process is stopped as the temperature again rises, before water vapor hits the condenser. Commercial uses for distilled alcohol: 1. fuel alternative to fossil fuels 2. industrial solvent 3. old disinfectant/sedative (isopropanol is made from petroleum gases) 4. beverages 5. preservative http://www.goafeni.com/images/distilation.jpg Fermentation (cont.) lactic acid fermentation note: - in several ways rather the same as alcohol fermentation: ~ NAD+ regenerated ~ unused product formed - in several ways this path unlike alcohol fermentation: ~ no CO2 formed (3C waste) ~ in bacteria, fungi and animals (such as yourself) ~ used to make yogurt ~ causes muscle pain in you ~ can’t solely sustain your life, merely supplements, during high exertion. Fermentation (cont.) - sometimes called anaerobic respiration (though techically some prokaryotes have full cellular respiration with an electron receptor other than oxygen…) - uses the same glycolysis, in cytosol, as aerobic respiration. - yields far less ATP per glucose: about 2 ATP net vs. up to 38 ATP because it doesn’t cash in e- via Krebs and ETC. - several points suggest glycolysis is oldest energy path: ~ not in mitochondrion ~ life predates atmospheric O2 by 0.8 billion years ~ most widespread metabolic pathway Glucose isn’t the only food that yields energy through aerobic respiration: simple sugars are enzymatically altered to enter in glycolysis protein parts can enter as pyruvate, acetic acid, or at various steps of the Krebs cycle. Nitrogen waste is disposed of as urea. lipids: the 3C glycerol backbone enters as G3P; fatty acids are hydrolyzed into 2 carbon acetates. Provide the differences between the fermentations we covered. cellular respiration redox reaction ATP proton-motive force ADP aerobic glycolysis chemiosmosis substrate-level phosphorylation electron transport chain NADH ATP synthase pyruvate oxidative phosphorylation link reaction cristae bridge reactions matrix decarboxylation fermentation Krebs cycle alcohol fermentation citric acid cycle lactic acid fermentation preparatory reaction