Glycogen Metabolism PDF
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Arizona State University
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This document explains glycogen metabolism, a crucial biochemical process involving the synthesis and breakdown of glycogen for glucose storage and release. It covers the different steps, including the involved enzymes and regulation. It is suitable for a biochemistry or biology related course.
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# Glycogen Metabolism ## Introduction Glucose, the preferred fuel for most cells, is generally acquired from the diet; however, organisms must continue to fuel their cells between feedings. Lesson 11.2 describes the process of gluconeogenesis, in which the liver can produce glucose during times of...
# Glycogen Metabolism ## Introduction Glucose, the preferred fuel for most cells, is generally acquired from the diet; however, organisms must continue to fuel their cells between feedings. Lesson 11.2 describes the process of gluconeogenesis, in which the liver can produce glucose during times of need. However, liver production of glucose may not be quick enough to satisfy the needs of vigorously contracting muscle, for example. Moreover, gluconeogenesis requires fuel to provide the carbon skeleton for the produced glucose, which may not be available between feedings. Instead of relying on gluconeogenesis, animal cells can store glucose in the form of a polysaccharide known as glycogen. As discussed in Lesson 7.2, storing glucose as glycogen provides cells quick access to large amounts of glucose without disrupting the osmolarity of the cell. This lesson describes the biochemical reactions through which glycogen molecules are synthesized and elongated (glycogenesis), the reactions through which glycogen is broken down (glycogenolysis), and the ways in which these processes are regulated. Figure 11.53 shows general information about glycogenesis and glycogenolysis. ### Anabolic conditions (eg, insulin stimulation) ### Catabolic conditions (eg, glucagon stimulation) | | | | | |------------------|-----|------------------|-----| | Glucose subunit | | Glucose subunit | | | | → | | → | | Glycogenesis | | Glycogenolysis | | | | → | | → | | Glycogenolysis | | Glycogenesis | | | | | Glyocgen | | ## 11.4.01 Glycogenesis Like any other metabolic process that involves use of glucose by the cell, the first step of glycogenesis is phosphorylation of glucose to glucose 6-phosphate (G6P). This is accomplished by hexokinase, the first enzyme of glycolysis. The G6P produced is not committed to any one pathway but can go down one of several pathways (eg, glycolysis, pentose phosphate pathway). To proceed down glycogenesis, G6P must be further activated before it can be added to an existing glycogen polymer. ### Activation of Glucose for Glycogenesis The glucose derivative that reacts in the glycogen elongation reaction is UDP-glucose, which has a uridylyl functional group (ie, a uridine nucleotide) attached to carbon 1. Therefore, to further activate glucose 6-phosphate for glycogen synthesis, the phosphate group must be moved to carbon 1 and a uridylyl group must be transferred onto the phosphate. These reactions activate the anomeric carbon - and therefore the reducing end - of the incoming glucose, which allows it to later form a glycosidic bond with a nonreducing end of the growing glycogen molecule. The enzyme that moves the phosphate group from carbon 6 to carbon 1 is phosphoglucomutase. The conversion of glucose 6-phosphate into glucose 1-phosphate is reversible under physiological conditions and is shown in Figure 11.54. $$-2O₃PO$$ 
