Glucose (GLOO-kose) is a simple sugar used by plants and animals to obtain the energy they need to stay alive and to grow. It is classified chemically as a monosaccharide, a compound whose molecules consist of five- or six-membered carbon rings with a sweet flavor. Other common examples of monosaccharides are fructose and galactose. Glucose usually occurs as a colorless to white powder or crystalline substance with a sweet flavor. It consists in two isomeric forms known as the D configuration and the L configuration. Dextrose is the common name given to the D conformation of glucose.
Dextrose; grape sugar; corn sugar; blood sugar
Carbon, hydrogen, oxygen
146°C (300°F); decomposes
Very soluble in water; slightly soluble in alcohol; insoluble in most organic solvents
Credit for the discovery of glucose is often given to the German chemist Andreas Sigismund Marggraf (1709–1782). In 1747, Marggraf isolated a sweet substance from raisins that he referred to as einer Art Zücker (a kind of sugar) that we now recognize as glucose. More than 60 years later, the German chemist Gottlieb Sigismund Constantine Kirchhof (1764–1833) showed that glucose could also be obtained from the hydrolysis of starch and that starch itself was nothing other than a very large molecule (polysaccharide) composed of many repeating glucose units. The molecular structure for glucose was finally determined in the 1880s by German chemist Emil Fischer (1852–1919), part of the reason for which he was awarded the 1902 Nobel Prize in chemistry.
HOW IT IS MADE
Glucose is synthesized naturally in plants and some single-celled organisms through the process known as photosynthesis. In this process, sunlight catalyzes the reaction between carbon dioxide and water that results in the formation of a simple carbohydrate (glucose) and oxygen. The overall reaction can be summarized by a rather simple chemical equation:
6CO2 + 6H2O → C6H12O6 + 6O2
However, photosynthesis actually involves a number of complex reactions that occur in two general phases, the light reactions and the dark reactions.
Glucose is produced commercially through the steam hydrolysis of cornstarch or waste products containing cellulose (a large molecule composed of glucose units) using a dilute acid catalyst. The product thus obtained is typically not very pure, but is contaminated with maltose (a disaccharide consisting of two molecules of glucose joined to each other) and dextrins (larger molecules consisting of a number of glucose units joined to each other).
- The name glucose comes from the Greek word gleucos for "sweet wine."
COMMON USES AND POTENTIAL HAZARDS
Glucose is the primary chemical from which plants and animals derive energy. In cells, glucose is broken down in a complex series of reactions to produce energy with carbon dioxide and water as byproducts.
Glucose also has a number of commercial uses, nearly all of them related to the food processing business. It is used in the production of confectionary products; chewing gum; soft drinks; ice creams; jams, jellies, and fruit preparations; baby foods; baked products; and beers and ciders. A relatively small amount is used for non-food purposes, primarily in the production of other organic chemicals, such as citric acid, the amino acid lysine, insulin, and a variety of antibiotics.
The most important health problem associated with glucose is diabetes. Diabetes is a medical condition that develops when the body either does not produce adequate amounts of insulin or cannot use that compound properly. Insulin is a hormone that controls the metabolism of glucose in the body. If glucose is not metabolized properly, a person's body acts as if it is "starving." Symptoms of diabetes include excessive hunger, weight loss, and exhaustion. If left untreated, the condition can result in coma and death. Diabetics must have an artificial source of insulin (usually from injections) and watch their diets to keep these symptoms under control.
Words to Know
- A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure.
- The process by which a compound reacts with water to form two new compounds.
- Two or more forms of a chemical compound with the same molecular formula, but different structural formulas and different chemical and physical properties.
- A process that includes all of the chemical reactions that occur in cells by which fats, carbohydrates, and other compounds are broken down to produce energy and the compounds needed to build new cells and tissues.
FOR FURTHER INFORMATION
"All about Diabetes." American Diabetes Association. http://www.diabetes.org/about-diabetes.jsp (accessed on October 10, 2005).
"Carbohydrates." Kimball's Biology Pages. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Carbohydrates.html (accessed on October 10, 2005).
"Dextrose, Anhydrous." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/D0835.htm (accessed on October 10, 2005).
"Glucose." Department of Chemistry, Imperial College London. http://www.ch.ic.ac.uk/vchemlib/mim/bristol/glucose/glucose_text.htm (accessed on October 10, 2005).
glucose, dextrose, or grape sugar, monosaccharide sugar with the empirical formula C6H12O6 . This carbohydrate occurs in the sap of most plants and in the juice of grapes and other fruits. Glucose is a normal component of animal blood; it thus requires no digestion prior to absorption into the bloodstream. Glucose can be obtained by hydrolysis of a variety of carbohydrates, e.g., milk and cane sugars, maltose, cellulose, or glycogen, but it is usually manufactured by hydrolysis of cornstarch with steam and dilute acid; the corn syrup thus obtained contains also some dextrins and maltose. Glucose is used in the manufacture of candy, chewing gum, jams, jellies, table syrups, and other foods, and for many other purposes. It is the major source of energy in animal metabolism. Glucose tastes only about three-fourths as sweet as table sugar (sucrose). The presence of glucose can be detected by use of Fehling's solution; various modifications of this test are used to detect glucose in urine, which may be a symptom of diabetes.
Alan W. Cuthbert
See blood sugar; metabolism.
The major dietary carbohydrates are starches, which are polymers of glucose and disaccharides: sucrose (glucose‐fructose); lactose (glucose‐galactose); maltose and isomaltose, which are dimers of glucose.
It is used in the manufacture of confectionery, since its mixture with fructose prevents sucrose from crystallizing (see boiled sweets); it is 74% as sweet as sucrose.
glu·cose / ˈgloōkōs/ • n. Biochem. a simple sugar, C6H12O6, that is an important energy source in living organisms and is a component of many carbohydrates. ∎ a syrup containing glucose and other sugars, used in the food industry.