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Basal Metabolic Rate • • • • • Minimum energy required to stay alive Kj / g / hr Measured at rest In thermostatically controlled room No food in previous 12 hours • What factors would affect your BMR? Breathing and cell respiration are not the same but are related O2 BREATHING CO2 Lungs CO2 Bloodstream O2 Muscle cells carrying out CELLULAR RESPIRATION Sugar + O2 ATP + CO2 + H2O Cellular respiration uses oxygen and glucose to produce carbon dioxide, water, and ATP. Glucose Oxygen Carbon dioxide Water Energy How efficient is cell respiration? Energy released from glucose (as heat and light) Energy released from glucose banked in ATP Gasoline energy converted to movement About 40% 25% 100% Burning glucose in an experiment “Burning” glucose in cellular respiration Burning gasoline in an auto engine ATP = the universal energy currency Role of ATP in the human body The molecule ATP can be thought of as cash carrying a “piece of chemical energy” to wherever it’s needed. The mechanism responsible for cellular work is the transfer of a phosphate group (Pi). Enzymes shift a phosphate group from ATP to some other molecule. This molecule becomes phosphorylated, also known as activated, and can perform work. ATP itself is deactivated to ADP as its phosphate group is removed. For example, ATP activates transport proteins in cell membranes for active transport, motor proteins for muscular contractions or chemical substances for chemical reactions. Reduction and Oxidation OILRIG Oxidation is losing electrons (or gain of O, or loss of H) Reduction is gaining electrons (or loss of O, or gain of H) Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Glucose gives off energy as it is oxidised The coenzymes NAD+ and FAD act as an electron shuttle FAD + 2H FADH2 The mitochondrion Glycolysis https://www.youtube.com/watch?v=EfGlznwfu9U Occurs in the cytoplasm Breaks down glucose (6 C) into 2 pyruvate (3 C) Produces 2 ATP molecules + 2 NADH Glycolysis Glycolysis Steps 1 – 3 A fuel molecule is energized, using ATP. Glucose Step 1 Glucose-6-phosphate 2 Fructose-6-phosphate Energy In: 2 ATP 3 Fructose-1,6-diphosphate Step 4 A six-carbon intermediate splits into two three-carbon intermediates. 4 Glyceraldehyde-3-phosphate (G3P) 5 Step 5 A redox reaction generates NADH. 6 Energy Out: 4 ATP Steps 6 – 9 ATP and pyruvic acid are produced. 1,3-Diphosphoglyceric acid (2 molecules) 7 3-Phosphoglyceric acid (2 molecules) 8 2-Phosphoglyceric acid (2 molecules) 2-Phosphoglyceric acid (2 molecules) NET 2 ATP 9 Pyruvic acid (2 molecules per glucose molecule) Link reaction Pyruvate is decarboxylated and dehydrogenated in the mitochondria if oxygen is available The products are CO2 and acetyl CoA (2 C) and NADH Pyruvic Acid Acetyl CoA The Krebs cycle (TCA cycle /citric acid cycle) In the mitochondial matrix https://www.youtube.com/watch?v=JPCs5pn7UNI Electron Transport System – oxidative phosphorylation https://www.youtube.com/watch?v=VER6xW_r1vc Protein complex Intermembrane Electron space carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE ATP Synthase, a molecular mill Generation of ATP Chemiosmosis Cells use the energy released by “falling” electrons in the ETS to pump H+ ions across a membrane. The H+ ions can only move back through the inner membrane via a special channel in ATP synthase. This drives the reaction between ADP and Pi, making ATP. Review of cellular respiration How each molecule of glucose yields many ATP Fermentation versus respiration Pyruvate, the end product of glycolysis, represents the fork in the catabolic pathways of glucose. Fermentation Respiration involves glycolysis, the Krebs cycle, and electron transport: an overview Respiration is a cumulative function of three metabolic stages, diagrammed in Figure 9.6: 1) Glycolysis 2) The Krebs cycle 3) The electron transport chain and oxidative phosphorylation The first two stages, glycolysis and the Krebs cycle, are the ___________ pathways that decompose glucose and other organic fuels. Glycolysis, which occurs in the ____________, begins the degradation by breaking glucose into two molecules of a compound called _____________. The Krebs cycle, which takes place within the _________________________, completes the job by decomposing a derivative of pyruvate to carbon dioxide. Thus, the carbon dioxide produced by respiration represents fragments of oxidized organic molecules. Some of the steps of glycolysis and the Krebs cycle are ___________ reactions in which ________________ enzymes transfer electrons from substrates to NAD+, forming ______________. In the third stage of respiration, the _________________________ accepts electrons from the breakdown products of the first two stages (usually via ____________) and passes these electrons from one molecule to another. At the end of the chain, the electrons are combined with _________________ and ______________ to form water. The energy released at each step of the chain is stored in a form the mitochondrion can use to make ATP. This mode of ATP synthesis is called _________________________ because it is powered by the redox reactions that transfer electrons from food to oxygen. The site of electron transport and oxidative phosphorylation is the _____________________ of the mitochondrion. Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration. A smaller amount of ATP is formed directly in a few reactions of glycolysis and the Krebs cycle by a mechanism called ____________________ phosphorylation. This mode of ATP synthesis occurs when an enzyme transfers a phosphate group from a substrate molecule to ______________. "Substrate molecule" here refers to an Respiration involves glycolysis, the Krebs cycle, and electron transport: an overview Respiration is a cumulative function of three metabolic stages, diagrammed in FIGURE 9.6: 1) Glycolysis 2) The Krebs cycle 3) The electron transport chain and oxidative phosphorylation The first two stages, glycolysis and the Krebs cycle, are the catabolic pathways that decompose glucose and other organic fuels. Glycolysis, which occurs in the cytosol, begins the degradation by breaking glucose into two molecules of a compound called pyruvate. The Krebs cycle, which takes place within the mitochondrial matrix, completes the job by decomposing a derivative of pyruvate to carbon dioxide. Thus, the carbon dioxide produced by respiration represents fragments of oxidized organic molecules. Some of the steps of glycolysis and the Krebs cycle are redox reactions in which dehydrogenase enzymes transfer electrons from substrates to NAD+, forming NADH. In the third stage of respiration, the electron transport chain accepts electrons from the breakdown products of the first two stages (usually via NADH) and passes these electrons from one molecule to another. At the end of the chain, the electrons are combined with hydrogen ions and molecular oxygen to form water (see FIGURE 9.5b). The energy released at each step of the chain is stored in a form the mitochondrion can use to make ATP. This mode of ATP synthesis is called oxidative phosphorylation because it is powered by the redox reactions that transfer electrons from food to oxygen. The site of electron transport and oxidative phosphorylation is the inner membrane of the mitochondrion (see FIGURE 7.17). Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration. A smaller amount of ATP is formed directly in a few reactions of glycolysis and the Krebs cycle by a mechanism called substrate-level phosphorylation (FIGURE 9.7). This mode of ATP synthesis occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP. "Substrate molecule" here refers to an organic molecule generated during the catabolism of glucose. The electron transport chain and oxidative phosphorylation Fig 9-15. Chemiosmosis couples the electron transport chain to ATP synthesis. NADH shuttles high-energy electrons extracted from food during glycolysis and the Krebs cycle to an electron transport chain built into the inner mitochondrial membrane. The gold arrow traces the transport of electrons, which finally pass to oxygen at the "downhill" end of the chain to form water. Most of the electron carriers of the chain are grouped into three complexes, each represented here by a purple blob embedded in the membrane. Two mobile carriers, ubiquinone (Q) and cytochrome c, move rapidly along the membrane, ferrying electrons between the three large complexes. As each complex of the chain accepts and then donates electrons, it pumps hydrogen ions (protons) from the mitochondrial matrix into the intermembrane space. Thus, chemical energy originally harvested from food is transformed into a proton-motive force, a gradient of H+ across the membrane. The hydrogen ions flow back, down their gradient, through a channel in an ATP synthase, another protein complex built into the membrane. The ATP synthase harnesses the proton-motive force to phosphorylate ADP, forming ATP. (This phosphorylation is called oxidative because it is driven by the loss of electrons from food molecules.) The use of an H+ gradient (protonmotive force) to transfer energy from redox reactions to cellular work (ATP synthesis, in this case) is called chemiosmosis. The catabolism of various food molecules