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Essential Knowledge 2.A.2: Organisms capture and store free energy for use in biological processes Slide 2 What can heterotrophs use to produce free energy? Heterotrophs can metabolize carbohydrates, lipids and proteins by hydrolysis Proteins Carbohydrates Amino acids Sugars Fats GlycerolFatty acids Glycolysis Glucose Glyceraldehyde-3- Pyruvate P NH 3 Acetyl CoA Citric acid cycle Oxidative phosphorylation Slide 3 Why are we talking about electron acceptors? Transferring electrons during a chemical reaction releases energy stored in organic molecules. This energy can be used to make ATP What are the electron acceptors of cellular respiration? NADH Glycolysis and Krebs cycle FADH 2 - Krebs cycle Slide 4 What do we call chemical reactions that involve the transfer of electrons? Oxidation-Reduction Reactions Redox Reactions When is a substance oxidized? When is it reduced? The substance that is donating the electrons is Oxidized The substance that is accepting the electrons is Reduced (reduced because it takes on e) Slide 5 becomes oxidized becomes reduced Slide 6 becomes oxidized becomes reduced Slide 7 Why use electron acceptors at all? Why not make ATP directly from glucose? Using electron acceptors allow for controlled use of energy. If all energy were released at once, a great deal of energy would be lost in the form of heat. Slow release of energy involving electron acceptors allows for more efficient use of the energy. Reduced electron acceptors like NADH are a form of stored energy. NADH passes electrons onto an electron transport chain Electrons are pulled through the electron transport chain in a series of steps that release energy to produce ATP Slide 8 Fig. 9-4 Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e + 2 H + 2 e + H + NAD + + 2[H] NADH + H+H+ H+H+ Nicotinami de (oxidized form) Nicotinami de (reduced form) Slide 9 What is the ultimate electron acceptor in cellular respiration? Oxygen which joins with Hydrogen to form water. Slide 10 Free energy, G (a) Uncontrolled reaction H2OH2O H 2 + 1 / 2 O 2 Explosive release of heat and light energy (b) Cellular respiration Controlled release of energy for synthesis of ATP 2 H + + 2 e 2 H + 1 / 2 O 2 (from food via NADH) ATP 1 / 2 O 2 2 H + 2 e Electron transport chain H2OH2O Slide 11 Cellular respiration has three stages: Glycolysis (breaks down glucose into two molecules of pyruvate) The citric acid cycle (completes the breakdown of glucose) Oxidative phosphorylation (accounts for most of the ATP synthesis) Slide 12 Where does glycolysis take place? Cytoplasm What occurs during glycolysis? Literally means sugar splitting 2 major phases Energy investment phase (requires 2 ATP) Energy payoff phase (produces 4 ATP, 2 NADH, and 2 Pyruvate) Slide 13 Energy investment phase Glucose 2 ADP + 2 P 2 ATPused formed 4 ATP Energy payoff phase 4 ADP + 4 P 2 NAD + + 4 e + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Glucose Net 4 ATP formed 2 ATP used2 ATP 2 NAD + + 4 e + 4 H + 2 NADH + 2 H + Slide 14 What is the process by which ATP is produced during glycolysis? Substrate Level Phosphorylation direct transfer of phosphate from organic compound to ADP by an enzyme to make ATP Enzyme ADP P Substrate Enzyme ATP + Product Slide 15 Fig. 9-9-4 Glucose ATP ADP Hexokinase Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP ADP Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 1 2 3 4 5 Aldolase Isomerase Fructose- 1, 6- bisphosphate Dihydroxyacet one phosphate Glyceraldehy de- 3-phosphate 4 5 Slide 16 Fig. 9-9-9 Triose phosphate dehydrogenase 2 NAD + NADH 2 2 2 2 2 2 2 ADP 2 ATP Pyruvate Pyruvate kinase Phosphoenolpyruvate Enolase 2 H 2 O 2-Phosphoglycerate Phosphoglyceromutase 3-Phosphoglycerate Phosphoglycerokinase 2 ATP 2 ADP 1, 3-Bisphosphoglycerate + 2 H + 6 7 8 9 10 2 2 ADP 2 ATP Phosphoenolpyruvate Pyruvate kinase 2 Pyruvate 10 2 P i Slide 17 How does the process of glycolysis support the theory of evolution? Glycolysis is a metabolic pathway that has been conserved across all domains. Ancient prokaryotes probably used glycolysis to produce energy no need for oxygen / little oxygen in atmosphere for cellular respiration It is the most widespread metabolic pathway among Earths organisms suggesting that it evolved very early in the history of life