Glucose are termed glucans. Glucose is produced by plants through the photosynthesis using sunlight, water and carbon dioxide and can be used by all living organisms as an energy and carbon source. However, most glucose does not occur in its free form, but in the form of its polymers, i.e. lactose, sucrose, starch and others which are energy reserve substances, and cellulose and chitin, which are components of the cell wall in plants or fungi and arthropods, respectively. These polymers are degraded to glucose during food intake by animals, fungi and bacteria using enzymes. All animals are also able to produce
Glucose The free energy of formation of α-D-glucose is 917.2 kilojoules per mole. In humans, gluconeogenesis occurs in the liver and kidney, but also in other cell types. In the liver about 150 g of glycogen are stored, in skeletal muscle about 250 g.<ref name="Löffler/Petrides 389">Peter C. Heinrich: "Löffler/Petrides Biochemie und Pathobiochemie." Springer-Verlag, 2014, , p. 389. (german)</ref> However, the glucose released in muscle cells upon cleavage of the glycogen can not be delivered to the circulation because glucose is phosphorylated by the hexokinae, and a glucose-6-phosphatase is not expressed to remove the phosphate group. Unlike for glucose, there is no