Lecture 39 Glycogenolysis and Glycogenesis

Lecture 39 Glycogenolysis and Glycogenesis - Glycogenolysis...

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Glycogenolysis and Glycogenesis Liver - tremendous capacity for storing glycogen. In the well-fed human, liver glycogen content can account for as much as 10% of wet weight of this organ. 1. Liver glycogen levels vary greatly in response to the intake of food 2. is mobilized to help maintain a nearly constant blood glucose level. 3. Liver glycogen is called into play between meals and to a greater extent during the nocturnal fast. 4. In both humans and the rat, the store of liver glycogen lasts somewhere between 12 and 24 h during fasting, depending greatly, of course, on whether the individual under consideration is caged or running wild. Muscle - stores less when expressed on the same basis—a maximum of only 1–2% of its wet weight. However, the average person has more muscle than liver, adding up to about twice as much total muscle glycogen as liver glycogen. 1. Serves as a fuel reserve for the synthesis of ATP within that tissue 2. Muscle glycogen is a source of ATP for increased muscular activity. (for themselves – high demand of activity) 3. Broken down without formation of free glucose. 4. Conversion of glucose to glycogen in muscle plays an important role in lowering 5. blood glucose levels elevated by a high-carbohydrate meal. Glycogenesis in liver 6. also contributes to the lowering of blood glucose but may be less important in this 7. regard than glycogen synthesis in muscle. Both Muscle and Liver play important roles in managing blood glucose (esp. after meals) Exercise 1. triggers mobilization of muscle glycogen for formation of ATP. a. 2 situations 2. The yield of ATP and the fate of the carbon of glycogen depend on whether the muscle fiber is “white” or “red.” a. Each fiber meets a different situation b. Burst of strength vs. endurance exercise Red Muscle Fibers – aerobic respiration – lasts long 1. supplied with a rich blood flow 2. Contain large amounts of myoglobin 3. Packed with mitochondria. 4. Glycogen mobilized within these cells is converted into pyruvate, which, because of the availability of O2 and mitochondria, can be converted into CO2 and H2O 5. Advantage of mitochondria = generate a lot more ATP 6. Endurance exercise White Muscle Fiber – not efficient 1. have less myoglobin and fewer mitochondria 2. Glycogenolysis within this tissue supplies substrate for glycolysis, with the end product being primarily lactate 3. White muscle fibers have enormous capacity for glycogenolysis and glycolysis, much more than red muscle fibers 4. Since their glycogen stores are limited, however, white muscle fibers can only function at full capacity for relatively short periods of time
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Lecture 39 Glycogenolysis and Glycogenesis - Glycogenolysis...

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