Glucose

OVERVIEW

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.

KEY FACTS

OTHER NAMES:

Dextrose; grape sugar; corn sugar; blood sugar

FORMULA:

C₆H₁₂O₆

ELEMENTS:

Carbon, hydrogen, oxygen

COMPOUND TYPE:

Carbohydrate (organic)

STATE:

Solid

MOLECULAR WEIGHT:

180.16 g/mol

MELTING POINT:

146°C (300°F); decomposes

BOILING POINT:

Not applicable

SOLUBILITY:

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).

Interesting Facts

• 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

CATALYST

A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure.

HYDROLYSIS

The process by which a compound reacts with water to form two new compounds.

ISOMERS

Two or more forms of a chemical compound with the same molecular formula, but different structural formulas and different chemical and physical properties.

METABOLISM

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).

See AlsoFructose; Sucrose

glucose is an important source of fuel for the body, especially for the brain and for red blood cells, which use no other fuel. Chemically glucose is a hexose sugar or monosaccharide — that is, a sugar with 6 carbon atoms and the formula C₆H₁₂O₆. Most glucose in the body is derived from the digestion of polysaccharides and other sugars: starch, for example, is polyglucose; common sugar, or sucrose, a disaccharide, is one molecule of glucose combined with one of fructose. In blood the level of glucose is around 90 mg per 100 ml. Glucose is stored in the body in the form of glycogen in body cells, especially in the liver and muscle, and is metabolized in tissues to generate the adenosine triphoshate (ATP) which provides energy.

Alan W. Cuthbert

glucose A six‐carbon monosaccharide sugar (hexose), with the chemical formula C₆H₁₂O₆, occurring free in plant and animal tissues and formed by the hydrolysis of starch and glycogen. Also known as dextrose, grape sugar, and blood sugar.

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.

glucose (dextrose; grape sugar) A white crystalline sugar, C₆H₁₂O₆, occurring widely in nature. Like other monosaccharides, glucose is optically active: most naturally occurring glucose is dextrorotatory. Glucose and its derivatives are crucially important in the energy metabolism of living organisms. It is a major energy source, being transported around the body in blood, lymph, and cerebrospinal fluid to the cells, where energy is released in the process of glycolysis. Glucose is present in the sap of plants, in fruits, and in honey and is also a constituent of many polysaccharides, most notably of starch and cellulose. These yield glucose when broken down, for example by enzymes during digestion.

glucose (dextrose) Colourless crystalline sugar (C₆H₁₂O₆) occurring in fruit and honey. It requires no digestion before absorption. Insulin lowers the blood-glucose level by causing the liver to convert glucose into glycogen. A monosaccharide sugar, it is prepared commercially by the hydrolysis of starch using hydrochloric acid.