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Transcript
Ch. 9: Cellular Respiration • The process by which cells break down glucose (C6H12O6), or a nutrient that has been converted to glucose or one of its simpler products, into carbon dioxide (CO2) and water (H2O). • Potential energy stored in covalent bonds is released (heat and ATP are produced). ATP allows cells to do work. TERMS TO KNOW • Coenzyme: a nonprotein organic molecule that plays an accessory role in enzyme-catalyzed reactions, often acting as a donor or acceptor of electrons. NAD+ is a coenzyme that becomes NADH when reduced (receives H electrons) • Endergonic reaction: a chemical reaction to which energy from an outside source must be added before the reaction can proceed (the reactants contain less energy than the products) • Exergonic reaction: energy-yielding and tends to proceed spontaneously (reactants contain more energy than the products and excess energy is released) TERMS TO KNOW • Activation energy: energy required to destabilize chemical bonds to initiate a chemical reaction • Oxidation: loss of an electron by an atom or molecule • Reduction: gain of an electron by an atom or molecule. Oxidation-reduction reactions transfer energy in living systems. Fig. 9.3 Fig. 9.4 Making ATP from Glucose Catabolism • Substrate level phosphorylation: a phosphate is transferred directly to ADP (glycolysis) • Aerobic Respiration: Electrons (H+) are harvested, transferred along the (Electron Transport Chain) making ATP (chemiosmosis) and finally donated to O2, releasing H2O Cellular Respiration - Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. 6O2 + C6H12O6 -> 6CO2 +6H2O + ATP+heat (reactants) (products) - Three Stages of Cellular Respiration: 1. glycolysis 2. Krebs Cycle (citric acid cycle) 3. Electron Transport Fig. 9.6 Fig. 9.7 Cellular Respiration • Glycolysis: 1. requires no oxygen (anaerobic) 2. occurs in the cytosol catalyzed by enzymes 3. 2 molecules of ATP are used to break one molecule of glucose in 1/2, producing two molecules of pyruvic acid (still containing most of the energy of the original glucose molecule), NADH (containing high energy electrons), and 4 molecules of ATP Glycolysis cont. • A small portion of the energy in the glucose is released and some makes 4 molecules of ATP (substrate-level phosphorylation) • Remainder of small portion of energy released (H+) are transferred to an energy trransferring molecule(NAD+) which then become NADH. Pyruvate Pathways • • Cells harvest energy from the electrons of covalents bonds of molecules. The energy depleted electrons associated with a proton as a hydrogen atom that are used to make ATP are donated to other molecules. A) Aerobic Respiration: Pyruvate is oxidized into carbon dioxide (released) and acetyl-CoA in the Krebs Cycle. Eventually, oxygen gas accepts the high energy H atoms of NADH and FADH2 created in the rest of the Krebs Cycle and water is created as a waste product (electron transport chain in the membrane of the mitochondria) B) Anaerobic Respiration: Pyruvate molecules are reduced to lactate and NADH is oxidized to NAD+ to replenish the NAD+ for further glycolysis. (some bacteria, fungi, and muscle cells). Used to make cheese and yogurt. C) Fermentation: Pyruvate is reduced to ethanol alcohol and gives off 2 molecules of CO2 as well (bacteria and yeast) which is used in the bread, beer and wine industries. Fig. 9.9 Krebs Cycle - Krebs Cycle (citric acid cycle) 1. requires oxygen (aerobic) 2. occurs in the inner membrane of mitochondria 3. pyruvic acid is oxidized into carbon dioxide (released) and acetylCoA. 4. Acetyl-CoA joins with a 4-carbon molecule and becomes citric acid 5. Citric acid is broken down, carbon dioxide is released, and 10 molecules of NADH and 2 molecules o FADH2 (both high energy electron molecules) are produced **If no oxygen is present, anaerobic respiration or fermentation will occur instead of the Krebs Cycle. Pyruvate is oxidized and becomes ethanol in grapes and bread dough and lactic acid in muscles. Cellular Respiration - Krebs Cycle (citric acid cycle) 1. requires oxygen (aerobic) 2. occurs in the inner membrane of mitochondria (where necessary enzymes are located) 3. pyruvic acid is oxidized into carbon dioxide (released) and acetylCoA. (co-enzyme) 4. Acetyl-CoA joins with a 4-carbon molecule and becomes citric acid 5. Citric acid is oxidized,more carbon dioxide is released, and 10 molecules of NADH and 2 FADH2 (high energy electron molecules) are produced 6. These high energy molecules and their accompanying protons move on to the ETC Cellular Respiration - Electron Transport: 1. The high energy electrons of NADH and FADH2 are transferred to special energy accepting molecules (Electron Transport System) within the cristae of the inner mitochondria 2. As energized electrons leap from one of these molecules to the next, their energy is used to pump their accompanying protons from the inner chamber of the mitochondria to the outer chamber. A concentration gradient builds, and special carrier proteins bring (pump) protons back in. The energy released from this pumping is used to convert ADP and a phosphate into 34 more ATP from each molecule of glucose (chemiosmosis) ETC cont. 3. De-energized electrons are then accepted by oxygen molecule and act as final electron acceptors 4. The electrons are reunited with their accompanying protons (H+) and water is formed and released If this final acceptor (O2) is not available, the electrons and H+ ions will not move down the ETC and no additional ATP will form in this step. **36 molecules of ATP represents 38% of total energy from glucose. Remaining 62% is given off as heat. Fig. 9.16 Fig. 9.17 Fig. 9.18 Fig. 9.19 Fig. 9.10 Fig. 9.24a Anaerobic Respiration Alcohol Fermentation Ex. Yeast activity in bread dough 1. Yeast break the sugar in the bread dough into pyruvate and NADH. The pyruvate is then broken down into acetaldehyde and CO2 gas (bread rises) 2. The acetaldehyde becomes the electron acceptor for NADH, and ethyl alcohol is produced (up to 12%). Fig. 9.24b Anaerobic Respiration Lactic Acid Fermentation 1. Muscle cells use NADH to convert pyruvate into lactate (ionized form of lactic acid) 2. Circulating blood removes excess lactate, but if production exceeds removal capability, lactic acid will build in muscles and interfere with function (and cause cramps)