{"id":483,"date":"2017-10-26T14:13:22","date_gmt":"2017-10-26T14:13:22","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/sunynutrition\/?post_type=chapter&p=483"},"modified":"2017-11-13T19:40:58","modified_gmt":"2017-11-13T19:40:58","slug":"6-22-glycogenesis-glycogenolysis","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-nutrition\/chapter\/6-22-glycogenesis-glycogenolysis\/","title":{"raw":"6.22 Glycogenesis & Glycogenolysis","rendered":"6.22 Glycogenesis & Glycogenolysis"},"content":{"raw":"
\r\n\r\nAs discussed earlier, glycogen is the animal storage form of glucose. If a person is in an anabolic state, such as after consuming a meal, most glucose-6-phosphate within the myocytes (muscle cells) or hepatocytes (liver cells) is going to be stored as glycogen. The structure is shown below as a reminder.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"468\"]\"\" Figure 6.221 Structure of glycogen1<\/sup>[\/caption]\r\n\r\n<\/div>\r\nGlycogen is mainly stored in the liver and the muscle. It makes up ~6% of the wet weight of the liver and only 1% of muscle wet weight. However, since we have far more muscle mass in our body, there is 3-4 times more glycogen stored in muscle than in the liver2. We have limited glycogen storage capacity. Thus, after a high-carbohydrate meal, our glycogen stores will reach capacity. After glycogen stores are filled, glucose will have to be metabolized in different ways for it to be stored in a different form.\r\n\r\n

Glycogenesis<\/h3>\r\n\r\nThe synthesis of glycogen from glucose is a process known as glycogenesis. Glucose-6-phosphate is not inserted directly into glycogen in this process. There are a couple of steps before it is incorporated. First, glucose-6-phosphate is converted to glucose-1-phosphate and then converted to uridine diphosphate (UDP)-glucose. UDP-glucose is inserted into glycogen by either the enzyme, glycogen synthase (alpha-1,4 bonds), or the branching enzyme (alpha-1,6 bonds) at the branch points3<\/sup>.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"921\"]\"\" Figure 6.222 Glycogenesis[\/caption]\r\n\r\n<\/div>\r\n

Glycogenolysis<\/h3>\r\n\r\nThe process of liberating glucose from glycogen is known as glycogenolysis. This process is essentially the opposite of glycogenesis with two exceptions: (1) there is no UDP-glucose step, and (2) a different enzyme, glycogen phosphorylase, is involved. Glucose-1-phosphate is cleaved from glycogen by the enzyme, glycogen phosphorylase, which then can be converted to glucose-6-phosphate as shown below3<\/sup>.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1104\"]\"\" Figure 6.223 Glycogenolysis[\/caption]\r\n\r\n<\/div>\r\n

References & Links<\/h3>\r\n\r\n1. http:\/\/en.wikipedia.org\/wiki\/File:Glycogen.png\r\n\r\n2. Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ, editors. (2006) Modern nutrition in health and disease. Baltimore, MD: Lippincott Williams & Wilkins.\r\n\r\n3. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.\r\n\r\n<\/div>","rendered":"
\n

As discussed earlier, glycogen is the animal storage form of glucose. If a person is in an anabolic state, such as after consuming a meal, most glucose-6-phosphate within the myocytes (muscle cells) or hepatocytes (liver cells) is going to be stored as glycogen. The structure is shown below as a reminder.<\/p>\n

\n
\"\"<\/p>\n

Figure 6.221 Structure of glycogen1<\/sup><\/p>\n<\/div>\n<\/div>\n

Glycogen is mainly stored in the liver and the muscle. It makes up ~6% of the wet weight of the liver and only 1% of muscle wet weight. However, since we have far more muscle mass in our body, there is 3-4 times more glycogen stored in muscle than in the liver2. We have limited glycogen storage capacity. Thus, after a high-carbohydrate meal, our glycogen stores will reach capacity. After glycogen stores are filled, glucose will have to be metabolized in different ways for it to be stored in a different form.<\/p>\n

Glycogenesis<\/h3>\n

The synthesis of glycogen from glucose is a process known as glycogenesis. Glucose-6-phosphate is not inserted directly into glycogen in this process. There are a couple of steps before it is incorporated. First, glucose-6-phosphate is converted to glucose-1-phosphate and then converted to uridine diphosphate (UDP)-glucose. UDP-glucose is inserted into glycogen by either the enzyme, glycogen synthase (alpha-1,4 bonds), or the branching enzyme (alpha-1,6 bonds) at the branch points3<\/sup>.<\/p>\n

\n
\"\"<\/p>\n

Figure 6.222 Glycogenesis<\/p>\n<\/div>\n<\/div>\n

Glycogenolysis<\/h3>\n

The process of liberating glucose from glycogen is known as glycogenolysis. This process is essentially the opposite of glycogenesis with two exceptions: (1) there is no UDP-glucose step, and (2) a different enzyme, glycogen phosphorylase, is involved. Glucose-1-phosphate is cleaved from glycogen by the enzyme, glycogen phosphorylase, which then can be converted to glucose-6-phosphate as shown below3<\/sup>.<\/p>\n

\n
\"\"<\/p>\n

Figure 6.223 Glycogenolysis<\/p>\n<\/div>\n<\/div>\n

References & Links<\/h3>\n

1. http:\/\/en.wikipedia.org\/wiki\/File:Glycogen.png<\/p>\n

2. Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ, editors. (2006) Modern nutrition in health and disease. Baltimore, MD: Lippincott Williams & Wilkins.<\/p>\n

3. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.<\/p>\n<\/div>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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