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Glycolysis, Krebs Cycle, and other Energy-Releasing Pathways All organisms produce ATP by releasing energy stored in glucose and other sugars. Plants make ATP during photosynthesis. All other organisms, including plants, must produce ATP by breaking down molecules such as glucose Aerobic respiration - the process by which a cell uses O2 to "burn" molecules and release energy This reaction takes place over the course of three major reaction pathways Glycolysis The Kreb's Cycle (TCA cycle) Electron Transport Chain Glycolysis (glyco = sugar; lysis = breaking) Goal: break glucose down to form two pyruvates Where: the cytoplasm Glycolysis produces 4 ATP's and 2 NADH, but uses 2 ATP's in the process for a net of 2 ATP and 2 NADH NOTE: this process does not require O2 and does not yield much energy The First Stage of Glycolysis Glucose (6C) is broken down into 2 (3Carbon molecules) (glyceraldehyde -3phosphate) This requires two ATP's The Second Stage of Glycolysis 2 PGAL's (3C) are converted to 2 pyruvates This creates 4 ATP's and 2 NADH's The net ATP production of Glycolysis is 2 ATP's Krebs's Cycle (citric acid cycle, TCA cycle) Goal: take pyruvate and put it into the Krebs's cycle, producing NADH and FADH2 Where: the mitochondria There are two steps o The Conversion of Pyruvate to Acetyl CoA o The Kreb's Cycle proper In the Krebs's cycle, all of Carbons, Hydrogens, and Oxygen in pyruvate end up as CO2 and H2O The Krebs's cycle produces 2 ATP's, 8 NADH's, and 2FADH2's per glucose molecule The Conversion of Pyruvate to Acetyl CoA for Entry Into the Kreb's Cycle 2 NADH's are generated 2 CO2 are released The Kreb's Cycle 6 NADH's are generated 2 FADH2 is generated 2 ATP are generated 4 CO2's are released Therfore, for each glucose molecule that enters into the Kreb's cycle (including the prepatory conversion to Acetyl CoA), the net production of products are: o 8 NADH o 2 FADH2 o 2 ATP o 6 CO2 Electron Transport Chain Goal: to break down NADH and FADH2, pumping H+ into the outer compartment of the mitochondria Where: the mitochondria In this reaction, the ETS creates a gradient which is used to produce ATP Electron Transport Chain typically produces 32 ATP's Net Energy Production from Aerobic Respiration Glycolysis: 2 ATP Kreb's Cycle: 2 ATP Electron Transport Phosphorylation: 32 ATP Each NADH produced in Glycolysis is worth 2 ATP (2 x 2 = 4) - the NADH is worth 3 ATP, but it costs an ATP to transport the NADH into the mitochondria, so there is a net gain of 2 ATP for each NADH produced in gylcolysis o Each NADH produced in the conversion of pyruvate to acetyl COA and Kreb's Cycle is worth 3 ATP (8 x 3 = 24) o Each FADH2 is worth 2 ATP (2 x 2 = 4) o 4 + 24 + 4 = 32 Net Energy Production: 36 ATP! o Anaerobic Respiration Goal: to reduce pyruvate, thus generating NAD+ Where: the cytoplasm Why: in the absence of oxygen, it is the only way to generate NAD+ and ADP Lactic Acid Fermentation o The product of Lactic Acid fermentation, lactic acid o This is the "burn" felt when undergoing strenuous activity The only goal of fermentation reactions is to convert NADH to NAD+ (to use in glycolysis). No energy is gained Note differences - fermentation - 2 ATP's produced, aerobic respiration - 36 ATP's produced Related Catabolic Processes - Beta Oxydation Fats consist of a glycerol backbone three fatty acids connected to it The body absorbs fats and then breaks off the fatty acids from the glycerol Glycerol is converted to glyceraldehyde phosphate, an intermediate of glycolysis The fatty acids are broken down into two-carbon units which are then converted to acetyl CoA. o An eight-carbon fatty acid can produce 4 acetyl CoA's o Each acetyl CoA is worth 12 ATP's (3 NADP, 1 FADH2, 1 ATP) o Therefore, this short fatty acid is worth 48 ATP's, a fat with three chains of this length would be worth 144 ATP's! o This is why fats are such a good source of energy, and are bad if you want to lose weight