glycogen

Examples of glycogen in the following topics:

• Connecting Other Sugars to Glucose Metabolism

  • Sugars, such as galactose, fructose, and glycogen, are catabolized into new products in order to enter the glycolytic pathway.
  • Glycogen, a polymer of glucose, is an energy-storage molecule in animals.
  • When there is adequate ATP present, excess glucose is shunted into glycogen for storage.
  • Glycogen is made and stored in both the liver and muscles.
  • The glycogen is hydrolyzed into the glucose monomer, glucose-1-phosphate (G-1-P), if blood sugar levels drop.

• Cell Signaling and Cellular Metabolism

  • The first enzyme promotes the degradation of glycogen by activating intermediate glycogen phosphorylase kinase (GPK) that in turn activates glycogen phosphorylase (GP), which catabolizes glycogen into glucose.
  • (Recall that your body converts excess glucose to glycogen for short-term storage.
  • When energy is needed, glycogen is quickly reconverted to glucose. ) Phosphorylation of the second enzyme, glycogen synthase (GS), inhibits its ability to form glycogen from glucose.
  • In this manner, a muscle cell obtains a ready pool of glucose by activating its formation via glycogen degradation and by inhibiting the use of glucose to form glycogen, thus preventing a futile cycle of glycogen degradation and synthesis.

• Food Energy and ATP

  • When the amount of ATP available is in excess of the body's requirements, the liver uses the excess ATP and excess glucose to produce molecules called glycogen (a polymeric form of glucose) that is stored in the liver and skeletal muscle cells.
  • When blood sugar drops, the liver releases glucose from stores of glycogen.
  • Skeletal muscle converts glycogen to glucose during intense exercise.
  • The process of converting glucose and excess ATP to glycogen and the storage of excess energy is an evolutionarily-important step in helping animals deal with mobility, food shortages, and famine.

• Pancreas

  • As blood glucose levels decline, alpha cells release glucagon to raise the blood glucose levels by increasing rates of glycogen breakdown and glucose release by the liver.
  • When blood glucose levels rise, such as after a meal, beta cells release insulin to lower blood glucose levels by increasing the rate of glucose uptake in most body cells, and by increasing glycogen synthesis in skeletal muscles and the liver.

• Hormonal Regulation of Metabolism

  • It also stimulates the liver to convert glucose to glycogen, which is then stored by cells for later use.
  • Glucagon raises blood glucose levels, eliciting what is called a hyperglycemic effect, by stimulating the breakdown of glycogen to glucose in skeletal muscle cells and liver cells in a process called glycogenolysis.
  • As the levels of glucose in the blood rise, insulin stimulates the cells to take up more glucose and signals the liver to convert the excess glucose to glycogen, a form in which it can be stored for later use.
  • When the levels of glucose in the blood fall, glucagon responds by stimulating the breakdown of glycogen into glucose and signals the production of additional glucose from amino acids.

• Carbohydrate Molecules

  • Starch, glycogen, cellulose, and chitin are primary examples of polysaccharides.
  • Glycogen is the storage form of glucose in humans and other vertebrates.
  • Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells.
  • Whenever blood glucose levels decrease, glycogen is broken down to release glucose in a process known as glycogenolysis.

• Hormonal Regulation of Stress

  • Epinephrine and norepinephrine increase blood glucose levels by stimulating the liver and skeletal muscles to break down glycogen and by stimulating glucose release by liver cells.
  • Glycogen reserves, which provide energy in the short-term response to stress, are exhausted after several hours and cannot meet long-term energy needs.
  • If glycogen reserves were the only energy source available, neural functioning could not be maintained once the reserves became depleted due to the nervous system's high requirement for glucose.
  • When an animal feels threatened, epinephrine and norepinephrine released by the adrenal medulla prepare the body to fight a threat or flee from it by breaking down stores of glycogen, which provides an immediate boost of energy.

• Metabolism of Carbohydrates

  • Plants store carbohydrates in long polysaccharides chains called starch, while animals store carbohydrates as the molecule glycogen.
  • Excess carbohydrates are stored as starch in plants and as glycogen in animals, ready for metabolism if the energy demands of the organism suddenly increase.

• Growth of Bone

  • In this zone, lipids, glycogen, and alkaline phosphatase accumulate, causing the cartilaginous matrix to calcify.
  • The next zone is the zone of maturation and hypertrophy where lipids, glycogen, and alkaline phosphatase accumulate, causing the cartilaginous matrix to calcify.

• Food Requirements and Essential Nutrients

  • The excess sugars in the body are converted into glycogen and stored in the liver and muscles for later use.
  • Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide energy during food shortage.