BCHM 307 1nd Edition Lecture 31 Outline of Last Lecture I Energy Production Pathway II Glycolysis Basics III The Ten Steps of Glycolysis Outline of Current Lecture I Alcoholic Fermentation A Steps in Alcoholic Fermentation II Anaerobic Glycolysis A Steps in Anaerobic Glycolysis III Gluconeogenesis A Irreversible Steps Current Lecture Sometimes glycolysis cannot take place in the normal fashion in a cell Alcoholic fermentation is another metabolic pathway that can occur This takes place in yeast in the absence of oxygen This process starts with pyruvate A hydrogen ion is added in the presence of the enzyme pyruvate decarboxylase Acetaldehyde and carbon dioxide is then formed through this nonreversible reaction The second step is a redox reaction It starts with acetaldehyde NADH and a hydrogen item The enzyme used is alcohol dehydrogenase Ethanol is the product formed in this reaction Another alternate pathway is anaerobic glycolysis This can occur in various microorganisms and in human active muscle tissue This also occurs in the absence of oxygen The enzyme used is lactate dehydrogenase This reaction starts with pyruvate NADH and a hydrogen ion NAD is regenerated as a product along with the final product of lactate Anaerobic glycolysis includes a process called the Cori cycle This cycle transports lactate through the bloodstream to the liver The lactate is oxidized into pyruvate while in the liver Pyruvate is then used in a process called gluconeogenesis to remake glucose The glucose is then transported back to the muscles through the bloodstream Gluconeogenesis uses the glycolytic intermediates to resynthesize glucose It is essentially a process of reverse glycolysis It uses almost all the same enzymes as glycolysis There are certain steps in glycolysis that are reversible steps 1 3 and 10 Therefore 4 new steps are used in gluconeogenesis in order to avoid these irreversible steps The steps of gluconeogenesis are listed below with only the new steps being listed The other steps are exact reversals of those in glycolysis Steps one and two of gluconeogenesis are used to compensate for step 10 of glycolysis It essentially does the reverse of pyruvate There is no net gain in carbon One ATP and one GTP are used to accomplish this 1 This step starts with pyruvate ATP is the energy source used and it is turned into ADP Carbon dioxide and water are also inputs Pyruvate carboxylase is the enzyme used in this reaction Oxaloacetate is formed along with an inorganic phosphate and two hydrogen ions 2 This step starts with oxaloacetate GTP is the energy source for this reaction Phosphoenolpyruvate carboxykinase is the enzyme used Phosphoenolpyruvate is formed along with GDP and carbon dioxide 9 The ninth step is the next changed step This step essentially accomplishes the reverse of phosphofructokinase in glycolysis step 3 This starts with fructose 1 6 bisphosphate and water This is turned into fructose 6 phosphate and inorganic phosphate The enzyme that accomplishes this is fructose1 6 bisphosphatase 11 This reaction essentially accomplishes the reverse of hexokinase in glycolysis step 1 Glucose 6phosphate is the starting material along with water This is turned into glucose and inorganic phosphate The enzyme that accomplishes this is glucose 6 phosphatase
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