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HOW CELLS HARVEST ENERGY (AKA CELLULAR RESPIRATION) CH 9 Energy is stored in the chemical bonds of organic molecules Breakdown of these large organic molecules releases ATP which is used for cellular work 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: o Glycolysis o Oxidation of pyruvate o Kreb’s cycle o Electron transport chain and oxidative phosphorylation 1. Glycolysis Occurs in ALL cells Occurs in the cytoplasm Breaks down glucose to 2 3-carbon molecules called pyruvate 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 3. Kreb’s cycle Occurs in the mitochondrial matrix 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_cycle_wor ks__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 eis 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 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 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 it acts as allosteric inhibitor to the 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 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 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 eacceptor. 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: