Glycogenesis - its process and mechanism, Lecture notes of Physiology

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GLYCOGENESIS

Process and Mechanism

After absorption into a cell, glucose can be used immediately for release of energy to the cell, or it can be stored in the form of glycogen, which is a large polymer of glucose.

Glycogenesis—Formation of Glycogen Glycogenesis is the biological process of forming glycogen from glucose. The body creates glycogen through the process of glycogenesis to store these molecules for later use, when the body does not have readily available glucose.

Glycogenesis is stimulated by the hormone insulin. Insulin facilitates the uptake of glucose into muscle cells, though it is not required for the transport of glucose into liver cells. However, insulin has profound effects on glucose metabolism in liver cells, stimulating glycogenesis and inhibiting glycogenolysis, the breakdown of glycogen into glucose.

The chemical reactions for glycogenesis are shown in Figure. From this figure, it can be seen that glucose-6-phosphate can become glucose-1- phosphate; this is converted to uridine diphosphate glucose, which is finally converted into glycogen.

Several specific enzymes are required to cause these conversions, and any monosaccharide that can be converted into glucose can enter into the reactions. Certain smaller compounds, including lactic acid, glycerol, pyruvic acid, and some deaminated amino acids, can also be converted into glucose or closely allied compounds and then converted into glycogen.

Epinephrine Epinephrine, also called adrenaline, is the hormone released in the fight-or-flight response. In other words, it is the chemical released when your body is frightened or stressed. Epinephrine negatively regulates glycogenesis, by disrupting the proteins necessary for the process.

During a flight-or-fight response, the body wants all the available energy ready for disposal by the cells. Thus, it stops glycogenesis, starts glycogenolysis, and starts converting the glucose into energy. The cells will need much ATP to overcome the threat presented.

Lots of glycogen is stored in the liver, which can then release it as glucose back into the bloodstream between meals to keep the blood glucose at tolerable levels.