Manufacturers use citric acid as a flavoring agent in soft drinks, fruit juices, and many other foods. Worldwide, the market for citric acid is valued at hundreds of millions of dollars per year. Commercial production uses the mold Aspergillus niger, which metabolizes sucrose under carefully controlled conditions. The yield of citric acid strongly depends on the concentration of FeCl, in the culture medium, as indicated in the graph. Why does the yield decrease when the concentration of Fe3+ is above or below the optimal value of 0.5 mg/L? A low level of Fe3+ supports the optimal activity of which contains Fe3+. Place the equations on the appropriate side of each step to show the sequence of reactions by which A. niger can synthesize citric acid from sucrose. Place the equations on the appropriate side of each step to show the sequence of reactions by which A. niger can synthesize citric acid from sucrose. sucrose +H2O glucose + 2P: + 2 ADP + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H20 2 pyruvate + 2 NAD+ + 2 COA 2 oxaloacetate + 2 ADP + 2 Pi + 4H+ - 2 citrate + 2 COA Answer Bank 2 acetyl-CoA + 2 oxaloacetate + 2 H20 2 pyruvate + 2 CO2 + 2 ATP + 2 H2O 2 acetyl-CoA + 2 NADH + 2 H+ 2 CO2 glucose + fructose fructose + 2 P + 2 ADP + NAD+ 2 pyruvate + 2 ATP + 2 NADH + 2H+ + 2H2O Complete the balanced equation for the overall reaction. Complete the balanced equation for the overall reaction. Sucrose + + + + + + + + Does the commercial process require aerated culture medium—that is, is this a fermentation or an aerobic process? an aerobic process, because A. niger cells must use O2 to continuously regenerate NAD a fermentation process, because A. niger cells cannot use Oą to continuously regenerate NAD+ an aerobic process, because A. niger cells cannot use O2 to continuously regenerate NAD+ a fermentation process, because A. niger cells must use 02 to continuously regenerate NAD+
