Glycogen Synthesis or Glycogenesis http www youtube comwatch

Glycogen Synthesis (or Glycogenesis)

http: //www. youtube. com/watch? v=h 6 qgfpin. Oy. Y

Definition: It is the formation of glycogen, which occurs in all tissues of the body, but in large amount in liver and muscles. There are very small amount of glycogen synthesis and storage in the central nervous system; this is why it is completely dependent on blood glucose as a source of energy. Site: Cytosol of all cells particularly liver and muscles.

Sources of glucose: A-For liver glycogen: • Blood glucose • Other hexoses: fructose and galactose • Non-carbohydrate sources: “gluconeogenesis”, e. g. , amino acids, glycerol and lactate during fed state. B-For muscle glycogen: • blood glucose only.

The Sugar Nucleotide UDP-Glucose Donates Glucose for Glycogen Synthesis

Regulation of Glycogen Synthesis

Glycogen Breakdown (or Glycogenolysis)

Definition: It is the process of glycogen catabolism (or breakdown) into: Glucose to blood, in the liver. Or, Glucose-6 -phosphate Lactic acid, in the muscles. Site: Cytosol of all cells but high activity in liver and muscles.

Regulation of Glycogenolysis

http: //www. youtube. com/watch? v=h 6 qgfpin. Oy. Y

Glycogen Storage Diseases

Definition: Glycogen storage diseases are groups of inherited disorders characterized by deposition (over-storage) of an abnormal type or quantity of glycogen or failure of storage of glycogen in the tissues. They are mainly due to deficiency of one of enzymes of glycogenesis or glycogenolysis, phosphofructokinase, or lysosomal glycosidases.

1 -Type I: Von Gierke’s disease: 2 -Type II: (Pompe’s disease): 3 -Type III: (Limit Dextrinosis, Forbe's disease): 4 -Type IV: (Andersen’s disease): 5 -Type V: (Mc. Ardle’s disease): 6 -Type VI: (Hers' disease): 7 -Type VII: (Tarui’s disease): 8 -Type VIII:

Gluconeogenesis

Is the formation of glucose from non-carbohydrate precursors. It is particularly important for tissues dependent on blood glucose such as RBCs and brain. The daily glucose requirements of the adult brain is 120 grams, whereas, the whole body requires 160 grams. The body stores are 210 grams (190 grams from liver glycogen and 20 grams in body fluids) enough for a day.

In a longer period of starvation, glucose must be formed from non-carbohydrate sources for survival. It also occurs during intense exercise. These non-carbohydrate precursors include lactate, pyruvate, propionate, glycerol (from diet and lipolysis) and glucogenic amino acids. Site: Mitochondria and cytosol of Liver and kidney are almost the only organs able to synthesize glucose from non-carbohydrate sources.

Gluconeogenesis from Glycerol • Glycerol absorbed from diet or derived from lipolysis of fat is activated by glycerol kinase in liver, kidney, lactating mammary gland, heart and intestine into glyerol-3 -phosphate. • Glyerol-3 -phosphate dehydrogenase oxidizes glyerol-3 -phosphate into dihydroxyacetonephosphate to cross glycolysis into glucose

Gluconeogenesis from Propionic Acid • Propionic acid is derived from, methionine, isoleucine, -oxidation of odd number fatty acid, cholesterol conversion into bile acids and large intestinal and ruminal fermentation of fibers • Microfloral fermentation of dietary fibers in human large intestine and rumen of ruminants produces volatile fatty acids (Propionic, acetic and butyric acids). • Propionic acid is the major source of glucose synthesized by gluconeogenesis in ruminants.

Gluconeogenesis from glucogenic amino acids

Gluconeogenesis from Lactate and Pyruvate (Cori's Cycle) • Cori's Cycle is the cycle illustrating the fate of lactic acid produced by active muscles and RBCs. • Lactate and/or pyruvate formed by the anaerobic oxidation of glucose from skeletal muscle glycogen or glycolysis in RBCs, diffuses to blood stream and is transported to the liver and the kidney where it is transformed into glucose by gluconeogenesis

• Pyruvate also leaves muscles as alanine after transamination particularly during long starvation, where muscle proteins break down. • Alanine goes to liver where transamination converts it back into pyruvate. • The glucose formed diffuses back to the blood to be used by various tissues.

Thank You Edited by Dr/Ali H. El-Far Lecturer of Biochemistry Fac. of Vet. Med. Damanhour Univ.