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Cell Respiration Cellular Respiration • Cells must extract energy from organic molecules to provide energy for the processes of life. • Main source of such chemical energy are carbohydrates, especially glucose C6H12O6. • Cell respiration’s general formula is as follows: Types of Respiration • Cellular respiration has 2 general Classifications: 1. Aerobic Respiration occurs in the presence of O2. 2. Anaerobic Respiration occurs in the absence of O2. Aerobic Respiration Aerobic Respiration occurs in 3 steps 1. Glycolysis - The splitting of glucose into 2 3-Carbon molecules 2. Krebs Cycle (or citric acid cycle) 3. Electron Transport Glycolysis •Glucose molecule is split into 2 molecules of PGAL by addition of energy from 2 molecules of ATP (remember ATP ADP releases energy) •Each PGAL molecule is changed by enzymes into 2 molecules of Pyruvic Acid (a 3 carbon molecule). This creates 1 NADH (an energy molecule like NADPH from photosynthesis), and 2 ATP molecules for each pyruvic acid, for a total of 2 NADH, and 4 ATP molecules. Anaerobic Respiration • Occurs in low Oxygen situations. • Far less efficient than aerobic respiration only yields 2 ATP per glucose molecule • Two types: – Lactic acid fermentation – Alcoholic fermentation Lactic Acid Fermentation • Occurs in human muscle tissue - causes pain under high exertion • Allows recharging of NADH to NAD+ so glycolysis can continue • Follows following formula: – Puruvic Acid + NADH NAD+ + Lactic Acid Alcoholic Fermentation • Is widely used commercially to produce alcoholic beverages • Allows recharging of NADH to NAD+ so glycolysis can continue • Follows following formula: • Puruvic Acid + NADH NAD+ + Alcohol + CO2 Krebs Cycle Occurs only in the presence of oxygen. Cycle is composed of nine steps, which is summarized as follows: Pyruvic acid releases a CO2 and joins a 4C molecule to form a 6C molecule of citric acid The citric acid releases 2 CO2 molecules to form 2 molecules of NADH from NAD+ The resultant 4C molecule creates 1 GTP from GDP (This will be converted to ATP later) The resultant 4C molecule creates 1 FADH2 from FAD+ (This will be converted to ATP later) Another molecule of NADH is formed from NAD+. The resultant 4C molecule reenters the cycle, and the process begins again. Electron Transport Cell must convert FADH2 and NADH to ATP 22 ATP molecules are produced through electron transport This occurs in a process similar to photosynthesis NADH & FADH2 deliver H+ ions (and electrons) to intermembrane space of mitochondria. As H+ concentration gradient increases in inter-membrane space. H+ ions diffuse back into matrix through a special protein called ATP synthetase. This enzyme uses this diffusion energy to generate ATP. Electrons are passed through several membrane proteins where they bind with 2 H+ ions and Oxygen to form a molecule of H2O. Thus, in aerobic respiration Oxygen is the final electron acceptor. Energy Totals Source Number ATP Produced Glycolysis 2 ATP Transport of NADH into Matrix. -2 ATP Krebs Cycle (ATP & GTP) 2 ATP Electron Transport (NADH & FADH2) 34 ATP NET TOTAL 36 ATP Energy Totals contd.