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Control of glucose levels


Controlling glucose levels is essential for energy production and storage and for proper maintenance of blood glucose levels. The body has come up with an elegant way to utilize many of the same enzymes to produce and break down glucose. As you can see in the figure below, glycolysis is the name of the metabolic pathway that converts glucose to the metabolite pyruvate after several intermediary steps, which produce various other metabolites, ATP, and NADH. Gluconeogenesis, where glucose is generated from pyruvate and other non-carbohydrate carbon substrates, is essentially the reverse pathway, with some exceptions. In the figure below, three steps in the metabolic pathway are marked with an asterisk* to indicate that they require a different enzyme and/or series of steps in gluconeogenesis. The other steps use the same enzymes for both glycolysis and gluconeogenesis. Use the information in the figure below to answer the questions in this passage.
Altogether, the steps without an asterisk have slightly positive ΔG values. Knowing that glycolysis is spontaneous process, what does this mean about the ΔG values of the steps with the asterisk?
Choose 1 answer: