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The Basics of Cellular Respiration (CP) Cell respiration: The process of breaking down “food” (glucose molecules) in the presence of oxygen, ATP molecules (cell energy molecules) are produced. Much of it happens in the mitochondria. Cell Respiration: Overall Equation • 1 gram of Glucose, when burned in the presence of oxygen, releases 3.811kcal of heat energy. • When the end phosphate group is released from ATP, .007 kcal is available for work. (1 calorie = amount of heat needed to raise temp.1o C. 1Calorie (Food Calorie) = 1 kilocalorie or 1000 calories) Cells don’t “burn” glucose as rapidly as combustion, but, instead gradually release its energy. The cell cannot use the amount of energy in a glucose molecule all at once. The cell uses energy in the smaller “packets” contained in ATP molecules. Both plant & animal cells must use cell respiration in order to provide the ATP molecules they need. Cell respiration also provides “carbon skeletons” used in formation of other organic compounds. Cellular respiration may be thought of as 3 major processes • 1) Glycolysis – anerobic process (no O2) listed separately in CP Bio Text • 2) Krebs cycle – aerobic process (uses O2) also called “Citric Acid Cycle” • 3) Electron Transport System (chain) aerobic (Oxidative phosphorylation) or E.T.O.P.) Part I - Glycolysis One molecule of glucose (6 carbons) is converted into two 3 carbon pyruvic acid molecules. • Glycolysis occurs in the cytosol of the cytoplasm and is considered anaerobic because no oxygen is required during this process. 2 ATP molecules needed to start the process. 4 ATP are actually produced, 2 ATP = net gain (Although the yield is small, the cell can use this process to produce thousands of ATPs in milliseconds.) Part II- Krebs cycle (Citric Acid Cycle) It is named for Hans Krebs who discovered it in 1953. (It is also called the citric acid cycle” because citric acid is formed at the start of the cycle.) 1) Pyruvic acid (from glycolysis) is converted to Acetyl “CoA” which is broken down into carbon dioxide (CO2) in a series of energy-extracting reactions. 2) It is an aerobic process (requires O2) & is located in the mitochondrion. The inner folds called cristae increases the surface area for chemical reactions involved in cell respiration.(more ATPS made) 3) For each 3-carbon pyruvic acid, 1 ATP is produced. Therefore a total of 2 ATPs are produced from one glucose. 4) Protons (H+ ions) and electrons are carried by special compounds (NADH & FADH2) from Krebs Cycle for use in the Electron Transport Chain. CO2 is given off from Krebs cycle. III) The Electron Transport System (chain) (Let’s call it E.T.) & Oxidative Phosphorylation. E.T. provides energy to produce the most ATPs of cell respiration 1) Takes place within the mitochondria. 2) Electrons are carried & ATPs are produced: High energy electrons from Krebs cycle are passed from one “electron carrier” to the next. • Electrons are passed from one carrier (cytochrome proteins) to the next in E.T. Modern Biology (Holt) Energy given off from this process permits ATP synthase located on the inner membrane to produce ATPs. 3) One glucose molecule is responsible for the gain of 34 ATP molecules from E.T. 4) Oxygen is the final electron acceptor in the chain. The O2, electrons are combined with hydrogen ions to produce H2O. • Due to the proton concentration gradient produced, the protons diffuse back across the membrane to the matrix, through ATP synthase enzyme complex. • This is called chemiosmosis. • It produces 34 ATPs. Modern Biology (Holt) ATP Final Tally from 1 glucose broken down through cell respiration. • Glycolysis = 2 ATPs • Krebs Cycle (Citric Acid Cycle) = 2 ATPs • Electron Transport System & Oxidative Phosphorylation (E.T.O.P.) = 34 ATPs Total = 38 ATPs