Use in living organisms Monosaccharides are the major fuel source for metabolism, and glucose is an energy-rich molecule utilized to generate ATP in almost all living organisms. Glucose is a high-energy substrate produced in plants through photosynthesis by combining energy-poor water and carbon dioxide in an endothermic reaction fueled by solar energy. When monosaccharides are not immediately needed, they are often converted to more space-efficient (i.e., less water-soluble) forms, often polysaccharides. In animals, glucose circulating the blood is a major metabolic substrate and is oxidized in the mitochondria to produce ATP for performing useful cellular work. In humans and other animals, serum glucose levels must be regulated carefully to maintain glucose within acceptable limits and prevent the deleterious effects of hypo- or hyperglycemia. Hormones such as insulin and glucagon serve to keep glucose levels in balance: insulin stimulates glucose uptake into the muscle and fat cells when glucose levels are high, whereas glucagon helps to raise glucose levels if they dip too low by stimulating hepatic glucose synthesis. In many animals, including humans, this storage form is glycogen, especially in liver and muscle cells. In plants, starch is used for the same purpose. The most abundant carbohydrate, cellulose, is a structural component of the cell wall of plants and many forms of algae. Ribose is a component of RNA. Deoxyribose is a component of DNA. Lyxose is a component of lyxoflavin found in the human heart. Ribulose and xylulose occur in the pentose phosphate pathway. Galactose, a component of milk sugar lactose, is found in galactolipids in plant cell membranes and in glycoproteins in many tissues. Mannose occurs in human metabolism, especially in the glycosylation of certain proteins. Fructose, or fruit sugar, is found in many plants and humans, it is metabolized in the liver, absorbed directly into the intestines during digestion, and found in semen. Trehalose, a major sugar of insects, is rapidly hydrolyzed into two glucose molecules to support continuous flight.
use in living organisms monosaccharides are the major fuel source for metabolism and glucose is an energy-rich molecule utilized to generate atp in almost all living organisms glucose is a high-energy substrate produced in plants through photosynthesis by combining energy-poor water and carbon dioxide in an endothermic reaction fueled by solar energy when monosaccharides are not immediately needed they are often converted to more space-efficient (ie less water-soluble) forms often polysaccharides in animals glucose circulating the blood is a major metabolic substrate and is oxidized in the mitochondria to produce atp for performing useful cellular work in humans and other animals serum glucose levels must be regulated carefully to maintain glucose within acceptable limits and prevent the deleterious effects of hypo- or hyperglycemia hormones such as insulin and glucagon serve to keep glucose levels in balance insulin stimulates glucose uptake into the muscle and fat cells when glucose levels are high whereas glucagon helps to raise glucose levels if they dip too low by stimulating hepatic glucose synthesis in many animals including humans this storage form is glycogen especially in liver and muscle cells in plants starch is used for the same purpose the most abundant carbohydrate cellulose is a structural component of the cell wall of plants and many forms of algae ribose is a component of rna deoxyribose is a component of dna lyxose is a component of lyxoflavin found in the human heart ribulose and xylulose occur in the pentose phosphate pathway galactose a component of milk sugar lactose is found in galactolipids in plant cell membranes and in glycoproteins in many tissues mannose occurs in human metabolism especially in the glycosylation of certain proteins fructose or fruit sugar is found in many plants and humans it is metabolized in the liver absorbed directly into the intestines during digestion and found in semen trehalose a major sugar of insects is rapidly hydrolyzed into two glucose molecules to support continuous flight