How does the mechanism described in \"b\" affect the catalytic activities of the

Question

How does the mechanism described in "b" affect the catalytic activities of the bi-functional enzyme? What allosteric effector is created or broken down? How does this affect the activity of Phosphofructokinase-1? (increase or decrease) How does this affect the activity of Fructose 1, 6-bisphosphatase-1? (increase or decrease) In the oxidative phase of the pentose phosphate pathway, energy is extracted from glucose 6-phosphate to produce NADPH and yield ribose 5-phosphate. The free-energy change for this process is large and exergonic. In the non-oxidative phase of the pentose phosphate pathway, a series of carbon swapping reactions regenerate glucose 6-phosphate from ribose 5-phosphate. These reactions do not consume energy (the overall standard free-energy change for the non-oxidative phase is close to zero), and the pathway is pushed in the forward direction by substrate concentration In cells that carry out fatty acid synthesis, the two phases of the pathway continuously cycle, from glucose 6-phosphate to ribose 5-phosphate and back to glucose 6-phosphate. If the oxidative phase releases energy (in the form of NADPH) but the non-oxidative phase doesn't consume any energy, how is it possible for them to keep cycling? Explain.

Explanation / Answer

Answer:

For each conversion of glucose 6-phosphate to ribose 5-phosphate, one carbon is lost as CO2. While the non-oxidative phase is energetically neutral (doesn’t spend energy), it serves to keep feeding more carbon atoms in the form of carbohydrate into the oxidative phase where they can be oxidized. Therefore, in the cycle of glucose 6- phosphate to ribose 5-phosphate and back to glucose 6-phosphate, carbon atoms on carbohydrate are continually being consumed and oxidized to CO2.

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