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HOW CELLS HARVEST ENERGY (AKA CELLULAR RESPIRATION) CH 9 Energy is stored in the chemical bonds of organic molecules carbs proteins fats Breakdown of these large organic molecules releases ATP which is used for work (primarily to drive endergonic reactions) Energy stored in chemical bonds is potential energy Energy released when those bonds are broken is kinetic energy I. Catabolism of glucose Cellular respiration = catabolism of glucose to produce ATP 3 types of cellular respiration: o Aerobic respiration (nearly all organisms) o Anaerobic respiration (only a few types of bacteria) o Fermentation (when aerobic can’t work) A. Aerobic Respiration Requires O2 Occurs in most organisms In eukaryotes, most of it occurs in the mitochondria Produces 36 ATP Occurs in 4 stages: Glycolysis Oxidation of pyruvate Kreb’s cycle Electron transport chain and oxidative phosphorylation Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion Cytosol ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation 1. Glycolysis Occurs in ALL cells Occurs in the cytoplasm Breaks down glucose to 2 3-carbon molecules called pyruvate Energy investment phase Glucose 2 ADP + 2 P 2 ATP used Energy payoff phase 4 ADP + 4 P 2 NAD+ + 4 e– + 4 H+ 4 ATP formed 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+ 2 Pyruvate + 2 H2O 2 ATP 2 NADH + 2 H+ RESULTS: ATP production 2 ATP used 4 ATP made Net yield = 2ATP NADH production 2 NADH made which go to ETC to make ATP Only 2 of the 36 ATP has been made THE REST OF THE ENERGY STORED IN GLUCOSE IS NOW IN THE PYRUVATES http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html 2. Oxidation of pyruvate Occurs in the mitochondria Converts pyruvate to acetyl CoA Produces NADH NADH produced goes to ETC to make ATP Fate of acetyl CoA: o It enters into the Kreb’s cycle to continue aerobic respiration o If too much glucose is broken down in glycolysis, the excess acetyl CoA is used to make fatty acids and triglycerides (too much sugar makes you fat) CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 Pyruvate 3 CO2 Coenzyme A Transport protein 3. Kreb’s cycle Occurs in the mitochondrial matrix Acetyl CoA 2 pyruvate CO2 NAD+ Co A NADH + H+ 2 Acetyl CoA Co A Co A Citric acid cycle 2 CO2 6 NAD+ 2 FADH2 6 NADH + 3 H+ 2 FAD 2 ADP + Pi 2 ATP Yield: For EACH glucose molecule 6 NADH 2 FADH2 2 ATP NADH and FADH2 go on to ETC to make ATP http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cy cle_works__quiz_1_.html 4. Electron Transport Chain Occurs on the inner membrane of the mitochondria Uses energy in NADH and FADH2 to make 32 ATP NADH and FADH2 donate e- to ETC As e- is moved thru ETC, the energy in e- is used to actively pump protons across the inner membrane NRG from the e- is now stored in the proton gradient As the protons diffuse down their concentration gradient, ATP synthase uses the energy in the gradient to make 32ATP by chemiosmotic phosphorylation The e- that was hopping thru ETC goes to O2 which acts as final acceptor of e4H+ +4e- + 202 →2H2O + H + H + H + H Protein complex of electron carriers Cyt c V Q ATP synthase + FADH 2 NADH (carrying electrons from food) NAD 1 2 H + /2O2 H2O FA D ADP + P i + ATP + H 1 Electron transport chain 2 Chemiosmosi s Oxidative phosphorylation http://www.science.smith.edu/departments/Biology/Bio231/etc.html http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter9/ Aerobic respiration: the big picture Electron shuttles span membrane CYTOSOL 2 NADH 6 NADH 2 NADH Glycolysis Glucose MITOCHONDRION 2 NADH or 2 FADH2 2 Pyruvate 2 Acetyl CoA + 2 ATP Citric acid cycle + 2 ATP Maximum per glucose: 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP About 36 or 38 ATP B. Regulation of Aerobic Respiration By feedback regulation Glucose + ADP +NAD + FAD → ATP +NADH +FADH2 High ATP means cell has enuf ATP and ATP acts like allosteric inhibitor to turn off 2nd enzyme in glycolysis (phosphofructokinase) High NADH means too much glucose is being broken down and the cell has enuf ATP it acts as allosteric inhibitor and inhibits oxidation of pyruvate High ADP means cell needs more ATP and ADP acts as allosteric activator to activate phosphofructokinase C. Aerobic respiration, small mammals and generation of heat In the cold, many small mammals will allow the proton gradient generated in the ETC to bypass ATP synthase Thus instead of making ATP the energy in the proton gradient is lost as heat to help maintain body temp D. Aerobic respiration in prokaryotes Almost identical to eukaryotes: Glycolysis Oxidation of pyruvate Kreb’s cycle ETC and chemiosmotic phosphorylation HOWEVER: Since they have no mitochondria, all of aerobic respiration takes place in the cytoplasm, and the ETC occurs on the cell membrane E. Anaerobic respiration Occurs in certain bacteria Has the same stages as aerobic respiration: Glycolysis Oxidation of pyruvate Kreb’s cycle ETC However, O2 is NOT the final e- acceptor. They use another molecule as the final e- acceptor CO2 SO2 F. Fermentation Occurs when not enuf O2 is available for aerobic respiration Produces limited ATP (only 2) when compared to aerobic respiration NADH produced in glycolysis is converted back to NAD to keep glycolysis running 2 types: lactic acid fermentation and alcoholic fermentation 1. Lactic acid fermentation Occurs in muscle cells when circulatory system can’t supply enuf O2 for aerobic respiration Produces lactic acid 2. Alcoholic fermentation Occurs in yeast cells Produces alcohol and CO2 The fate of pyruvates depends on the amount of oxygen: II. Catabolism of proteins and fats Animals eat proteins fats and carbs Within digestive tract proteins are digested to amino acids, starch and sucrose are digested to glucose, and fats are digested to acetyl CoA Amino acids, glucose and acetyl CoA diffuse out of small intestine to blood Circulatory system delivers these molecules to all cells and they enter into aerobic respiration at various points III. How photosynthesis and respiration work together Products of one are reactants of other o Glucose and oxygen made in photosynthesis enter into aerobic respiration o The carbon dioxide from aerobic respiration enters into photosynthesis