2. Aerobic versus anaerobic metabolism (30 points). a. Triose phosphate isomeras
ID: 218805 • Letter: 2
Question
2. Aerobic versus anaerobic metabolism (30 points). a. Triose phosphate isomerase (TIM) catalyzes the conversion of DHAP to GAP. Cells lacking TIM can stay alive, but only under aerobic conditions (in the presence of oxygen). Explain why (2-4 sentences). b. The "Pasteur effect," first observed by Louis Pasteur in the 1860s, describes the following phenomenon: A culture of E. coli bacteria, grown in the absence of oxygen, consumes large amounts of glucose and produces lactic acid. If this culture of bacteria is then supplied with oxygen, two observations are made: observation 1: production of lactic acid stops » .observation 2: the rate of glucose consumption decreases but the overall rate of cell growth remains constant provide an explanation for observation 1 (2-3 sentences) provide an explanation for observation 2 (2-3 sentences). i, ii,Explanation / Answer
a. Cells that lack triose phosphate isomerase can complete glycolysis using only G3P, but this generates only 2 ATP. In these cells under anaerobic conditions there is no net gain of ATP from glycolysis. Under aerobic conditions, the single pyruvate can be further oxidized to generate a little more ATP and the energy stored in NADH can be harvested through oxidation phosphorylation to generate even more ATP.Hence energy can be gained in form of ATP in aerobic condition and cells remain alive in aerobic environment.
b. In the absence of O2 , pyruvate is fermented into lactic acid as a means to regenerate NAD+, but only 2 ATP are produced per glucose molecule. In the presence of O2 , pyruvate enters the Citric Acid Cycle which produces additional ATP and NADH. The NADH from glycolysis and the Citric Acid Cycle gives electrons to the electron transport chain which can produce additional ATP. Because respiration (the Citric Acid Cycle and oxidative phosphorylation) produces 18x more ATP/glucose, less glucose is consumed.
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