Other Metabolic Pathways - MCAT Biological and Biochemical Foundations of Living Systems

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Question

The process of glycolysis is used by all cells of the body to turn glucose into ATP for cellular energy. When stores of glucose are low, however, the body can break down a form of stored glucose in the liver to increase glucose reserves.

What molecule is broken down by a phosphorylase in the liver to yield glucose-1-phosphate?

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Answer

Glycogen is the polymer form of glucose, stored in the liver and other tissues when glucose is abundant. When glucose levels are high, glucose-1-phosphate is assembled into branching chains of glycogen. When glucose levels fall, glycogen is broken down by glycogen phosphorylase back into glucose-1-phosphate units. These monomers can be used in glycolysis and cellular respiration. Glycogen is the first source of energy that is used when glucose stores are low.

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