Cambridge Encyclopedia :: Cambridge Encyclopedia Vol. 28

galactose - Structure and isomerism, Reactions, Metabolic disorders

A simple sugar (monosaccharide), found in the sugar of milk along with glucose; otherwise, it is rare in nature. Galactosaemia, a genetic defect leading to an inability to metabolize galactose, is very uncommon and requires dietary management.


Haworth projection of D-galactose



Fischer projection of D-galactose

Galactose (Gal) (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages.

Galactan is a polymer of the sugar galactose.

Galactose is a monosaccharide constituent, together with glucose, of the disaccharide lactose. The hydrolysis of lactose to glucose and galactose is catalyzed by the enzyme beta-galactosidase, a lactase. In the human body, glucose is changed into galactose in order to enable the mammary glands to secrete lactose.

Two studies have suggested a possible link between galactose in milk and ovarian cancer.

Structure and isomerism

The first and last -OH groups point the same way and the second and third -OH groups point the other way.

Reactions

Hydrolysis

Galactose and glucose are produced by hydrolysis of lactose by ß-galactosidase.

Metabolic disorders

There are 3 important disorders involving galactose:

Galactokinase deficiency causes cataracts and mental retardation.

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