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Cellular Respiration AP Biology Photosynthesis….then • Photosynthesis captures the sun’s energy and converts it to glucose • Cellular respiration is the breakdown of glucose to produce ATP • ATP is useable energy • This process is carried out by plants and every other organism in the various trophic levels Cellular Respiration C6H12O6 + 6O2 6CO2 +6 H2O This is the summary: showing beginning and end There are three stages in between Cellular Respiration • Occurs in three stages: • Glycolysis • Kreb’s Cycle • Electron Transfer Phosphorylation • Net ATP yield depends on whether oxygen is present ATP Yield • Anaerobic respiration yields two ATP • Aerobic respiration yields 36 ATP • Bacteria do not need much ATP • You depend on the aerobic pathway Glycolysis • This is the first stage for both aerobic and anaerobic respiration • The first energy releasing pathways to evolve were anaerobic • Glucose is converted to pyruvate Glycolysis Many steps: to convert glucose into pyruvate 2 ATP invested; 4 produced Glycolysis • Occurs in the cytoplasm • First step requires 2 ATP • The next steps form 4 ATP by substrate level phosphorylation • This is the direct transfer of a phosphate group from a substrate to some other molecule (in this case ADP) • Meanwhile , NAD picks up electrons and H liberated from the PGAL Glycolysis • Pyruvate and NADH are used in the next stage of aerobic respiration • If no oxygen is present, the pyruvate goes into a fermentation pathway • Produces either lactic acid or alcohol (ethanol) 2nd stage ( Krebs Cycle) • Pyruvate molecules enter the inner compartment of the mitochondria • Electrons and hydrogen carried by NADH are transferred to many coenzymes • A carbon is removed from each pyruvate and joins Coenzyme A, becoming Acetyl-CoA. • This molecule enters the Krebs cycle Krebs Cycle • Three functions: • Loads electrons and hydrogen onto NAD+ and FAD, making 6NADH2 and 2FADH2 • (This is important for ATP production in the 3rd stage) • Forms 2 ATP • Cycles back to oxaloacetate, which is the molecule that acetyl CoA reacts with to start the Krebs cycle Phosphorylation • Substrate level: production of ATP by transferring a phosphate group from an intermediate directly to an ADP • Oxidative: production of ATP from the reactions of an electron transport chain • Includes chemiosmosis H+ conc gradient Substrate level phosphorylation • An enzyme catalyses the joining of P to ADP • Happens during glycolysis and Krebs cycle Oxidative phosphorylation • (Each NADH molecule represents stored energy that can “fall” down the energy gradient with oxygen as the final acceptor) • Controlled release of energy • The ETC creates the H+ gradient 3rd stage • ATP formation kicks into high gear • Uses electron transfer chains and the enzyme ATP synthase • NADH2 and FADH2 give up electrons and hydrogen into the chains • H+ is pumped out to create a concentration gradient. When the H+ is released, ATP is formed Glycolysis In the Glycolysis stage 4 ATP molecules are produced ,but 2 ATP's are used in the process so the net yield is 2 ATP's. In this stage 2 NAD's become NADH's. Krebs Cycle BEFORE the cycle 2 NADH's are created in the creation of Acetyl Coenzyme A. IN the cycle 2 GTP's are created. 6 NADH's are created, & 2 FADH2's too. Electron Chain Every NADH produces 3 ATP's. We have 10 NADH's, therefore 30 ATP's are created. Every FADH2 produces 2 ATP's. We have 2 FADH2's, therefore 4 ATP's are created. Total Balance 2 ATP + 2GTP +34 ATP :38 ATP Glycolysis Krebs Cycle Electron Chain Total Alternative Energy Sources • Proteins, broken down into amino acids, can also be broken down into pyruvate and therefore enter the Krebs cycle • Fats, broken down into fatty acids and glycerol, can also enter the cycle at two different points, resulting in the same end result