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.
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 Z cker (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.
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).
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.
