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Transcript
Cellular Respiration Extracting energy from Organic compounds (food) California Science Standards #1f, 1g, 1i, 6d, 9a 1 What do we know? Photosynthesis – Occurs in autotrophs – Stores ENERGY – Produces glucose – CO2 + H2O C6H12O6 + O2 Cellular respiration – Occurs in autotrophs and heterotrophs – Releases ENERGY – Uses glucose – C6H12O6 + O2 CO2 + H20 2 3 Respiration is a combustion reaction Like the burning snack foods, the “burning” of food molecules (glucose) in cells produces CO2 and H20, and it is an exothermic process. •In exothermic reactions, the reactants contain more energy before the reaction than the products contain at the end of the reaction. (i.e: energy is released.) 4 Some key differences In the lab, the combustion released energy as heat (which increased the temp of the water in the test tube). This reaction occurred very quickly. – A cell cannot use heat to do cellular work, not to mention the fact that this large increase in temp would be dangerous! 5 Respiration “slows down” the combustion of glucose The energy from glucose is released slowly by many enzyme-catalyzed reactions during cell respiration. This released energy is used to make ATP. 6 Respiration uses energy stored in glucose to make ATP ATP is adenosine triphosphate and is the main stored form of energy in all cells ATP contains three phosphate groups (see pic: the negative charges repel one another so the ATP is “unstable”). When one is removed, energy is released. The released energy from ATP is used for cellular work. 7 8 ATP: The energy “currency” of a cell. All cellular work comes at the “expense” of ATP. 9 Cellular Respiration An Overview (“Map”) ATP ATP 10 Glycolysis First step of cellular respiration; occurs in the cytoplasm. Breaks apart 1 glucose molecule (6-C) into 2 pyruvic acid molecules (3-C each) Requires glucose and 2 ATP Produces pyruvic acid /pyruvate, NADH, and 2 ATP (net yield) – Pyruvic acid used later in Krebs cycle – NADH (transports electrons) used in electron transport chain (ETC) 11 STEP 3 Glucose 2 NADH C C C C C C STEP 1 -2 ATP 6-carbon compound P C C C C C C P STEP 2 2 molecules of PGAL P C C C C C C P 2 molecules of 3-C compound P C C C P P C C C P STEP 4 2 molecules of pyruvic acid C C C C C C 4 ATP 12 Cellular Respiration Check the Map… ATP ATP 13 Aerobic Respiration (one branch of cellular respiration) Requires oxygen Produces nearly 20x more ATP than is produced by glycolysis alone 2 major stages: – Krebs cycle – Electron transport chain Location: Mitochondria Begins with pyruvic acid that is modified to become acetyl-CoA 14 Krebs Cycle Occurs in the mitochondrial matrix Acetyl CoA binds to oxaloacetic acid producing citric acid. In reactions, the hydrogens are “stripped” off the organic compounds, releasing carbons as CO2 (waste). Produces CO2, NADH, FADH2, and 2 ATP 15 C Citric acid C C C C C C C C Oxaloacetic acid C C C C NADH Krebs Cycle 5-C compound C C C C C C NADH 4-C compound 4-C compound C C C C C C C C FADH2 NADH ATP 16 Electron Transport Chain Last stage of aerobic respiration Located on inner membrane folds (cristae) of mitochondrion cristae 17 (Mitochondrial MatrixLocation of R&P of Krebs Cycle) Electron transport chain is here 18 (ETS) a.k.a ATP synthase 19 Electron Transport, continued NADH and FADH2 contain high energy electrons. When NADH and FADH2 reach the ETC they lose H+ and e-. Their high-energy e- are passed along the ETC, and energy from the eis used to pump H+ (protons) to the outer compartment of the mitochondrion. Energy from diffusion of H+ back into the matrix is used to generate 34 ATP molecules (chemiosmosis) 20 21 ATP Synthase 22 Let’s Review the Summary Equation C6H12O6 + O2 CO2 + H20 – Glucose used in glycolysis – CO2 produced in Krebs cycle (completing the breakdown of glucose) What is the importance of Oxygen? – There must be a “final acceptor” of e- at the end of the ETC. If the last protein in the chain holds onto the ethere will be a “traffic jam” and no other e- will flow down the chain. – Result: H+ pumping stops, so H+ gradient disappears and there is no energy to drive the synthesis of ATP. – Oxygen is the final e- acceptor of the ETC, so it keeps the ETC “running”. 23 So oxygen is used in the ETC and this is where water is formed. – When oxygen accepts the e-, it also bonds with H+ to form H2O. 24 Total ATP From Cellular Respiration 34 25 Cellular Respiration Check the Map… ATP ATP 26 Fermentation (Anaerobic Respiration) No oxygen? No problem…(kind of) 2 types: lactic acid fermentation, alcoholic fermentation Pros: can regenerate NAD+ when short on O2 – Keeps glycolysis going (small net gain of ATP) Cons: Cannot produce additional ATP – Only unicellular organisms, like bacteria or yeast, can survive with the ATP made by glycolysis alone. – Some cells in multicellular organisms can switch to anaerobic respiration, but only for a short time. 27 Lactic Acid Fermentation Manufacture of yogurt, cheese Muscle cells – “Anaerobic exercise” (sprints) – Lactic acid build-up (muscle burn, fatigue, cramps) Glucose Pyruvic acid C C C C C C C C C NAD+ NADH + H+ Lactic acid C C C 28 Alcoholic Fermentation Basis of wine and beer industries – Yeast + fruit juice = alcohol Takes place when making bread – CO2 makes bread rise; alcohol evaporates Glucose Pyruvic acid C C C C C C C C C NAD+ CO2 C NADH + H+ Ethyl alcohol 2-C compound C C C C 29