Energy Storage and Use in body : Glycogen Metabolism and Gluconeogenesis

Energy Storage and Use      Carbohydrates are the primary energy source in the body. Only when the supply of carbohydrates becomes limited does the body turn to fats and proteins. Glycogen Metabolism    Glycogen is a polymer of glucose with a branching chain. It is the storage form of glucose in animal cells as starch is the storage form in plants. When glucose is present in abundance it is converted into glycogen by glycogenesis. Glycogen is stored particularly well in skeletal muscle and liver cells. When glucose availability drops glycogen can be converted back to glucose by a process called glycogenolysis. The glucose that becomes available in skeletal muscle can be used  by skeletal muscle while the glucose from liver cells is mostly released into the bloodstream for use by other cells in the body. Gluconeogenesis    Although fat and protein can be used as an energy source, glucose must be available at all times because the nervous tissue (particularly the brain) requires it. Glycogen reserves can supply it for a period of time but when glycogen reserves are depleted glucose must be synthesized from fat and protein by a process called gluconeogenesis.   By gluconeogenesis glucose can come from three sources: 1. Glycerol - A component of triglycerides. Glycerol can be converted into glycerol phosphate and enter the glycolytic pathway in reverse. 2. Lactate - Lactate can be converted into pyruvate and then enter the glycolytic pathway in reverse. 3. Amino Acids - Some amino acids can be converted after conversion to pyruvate. Others can be converted to oxaloacetic acid which can then be converted to phosphoenolpyruvate which can enter the glycolytic pathway in reverse.