The balance between catabolism and anabolism is tightly regulated to match the e

Question

The balance between catabolism and anabolism is tightly regulated to match the energy needs of an organism at any given time and to help conserve energy. As a part of this balancing act, the steps of glycolysis can be run NestedLessLess backwards NestedGreaterGreater in a process known as gluconeogenesis. In the scheme depicted on the left, the double arrows indicate that the step is catalyzed by the same enzyme in either direction. Separate curved arrows show those steps, for which a different enzymes catalyzes the forward and reverse reactions. These steps represent points in the metabolic pathway which are subject to regulation. By controlling which of the two enzymes is more active, the cell can either break down glucose for energy (catabolism) or synthesize glucose which is in turn converted to starch or glycogen for storage (anabolism). A. The interconversion of fructose-6-phosphate and fructose-1, 6-bisphosphate is catalyzed by the pair of enzymes: phosphofructokinase (PFK) and fructose bisphosphatase (FBP). In the table below, indicate which of these two enzymes would be more active under each of the specified conditions. Conditions: More active enzyme (use abbreviations) high level of ATP __________ high levels of glucose ________ high levels of NAD+ __________ high levels of NADH __________ high levels of ADP __________low levels of Krebs cycle intermediates ___________ B. Explain your reasoning for your answer to condition (1) in part A. C. AMP has been found to be an activator of PFK and an inhibitor of FBP. If AMP does not bind to the active site of either enzyme, how can it have these regulatory effects?

Explanation / Answer

Ans.

Sr.no. Active enzyme Reason 1 FBP High levels of ATP indicate energy charge is high and hence synthesis of glucose becomes dominant. 2 PFK Excess glucose inhibits FBP and helps in activity of PFK to break down the glucose and convert it to energy. 3 PFK High levels of NAD+ help in promoting gycolysis and generation of energy in the form of NADPH 4 FBP Continued glycolysis depends on presence of high NAD+ levels. NADPH levels get converted to NAD+ by promoting activity of FBP 5 PFK ADP is a raw material required for generation of ATP in glycolysis. Hence high ADP stimulates PFK to increase rate of energy generation in glycolysis. 6 FBP Low levels of Kreb cycle intermediates leads to accumulation of end products of glycolysis. Hence reverse glycolysis is activated and the enzyme FBP is activated

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