Every step of glycolysis has at least one purpose. For each of the following fou

Question

Every step of glycolysis has at least one purpose. For each of the following four steps of glycolysis match the step to the correct function given below. Note that enzymes are not specified in the given reactions. In this step, the molecule is phosphorylated to keep it in the cell. In this step, the molecule is split into two, both of which will become pyruvate. In this step, NADH is made. In this step, energy is stored as ATP. In this step, pyruvate is made. Which of the choices above best describes the purpose of the following step of glycolysis?

Explanation / Answer

Phosphorylation of fructose-6-phosphate

phosphorylation of fructose-6-phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-6-phosphate, producing fructose-1,6-bisphosphate.

In this pathway, phosphofructokinase is a rate-limiting enzyme. It is active when the concentration of ADP is high; it is less active when ADP levels are low and the concentration of ATP is high. Thus, if there is “sufficient” ATP in the system, the pathway slows down. This is a type of end product inhibition, since ATP is the end product of glucose catabolism.

Energy-releasing steps

So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules. Both of these molecules will proceed through the second half of the pathway, and sufficient energy will be extracted to pay back the two ATP molecules used as an initial investment and produce a profit for the cell of two additional ATP molecules and two even higher-energy NADH molecules.

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