Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage. Lactose makes up around 2-8% of the solids in milk. The name comes from the Latin word for milk, plus the -ose ending used to name sugars. Lactose is a disaccharide consisting of two subunits, a galactose and a glucose linked together. Its empirical formula is C₁₂H₂₂O₁₁ and its molecular weight is 342.3 g/mol. In the young of mammals, an enzyme called lactase (β1-4 disaccharidase) is secreted by the intestinal villi, and this enzyme cleaves the molecule into its two subunits for absorption.

Lactase

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Normally, as the young grow up, production of lactase gradually ceases, and they are then unable to metabolise lactose. This is perhaps an adaptation mechanism to enforce weaning of the young. This loss of lactase on maturation is also the default pattern in most adult humans. Many adults, with ancestry in Europe, the Middle East, India, and the Maasai of East Africa, have a version of the gene for lactase that is not disabled after infancy. This adaptation has led to the milking of sheep, cattle, goats and water buffalo. The process of retaining infant characteristics into adulthood is one of the simplest routes of adaptation, and is known as neoteny. The observation that at least some humans have made adaptations to lactose in the adult diet may cast doubt on some arguments by proponents of the Paleolithic diet, who argue that human metabolic needs have not changed since the last ice age.

See also

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• lactose intolerance
• Lac operon

Disaccharides

Лактоза | Laktose | Milchzucker | Lactosa | Laktozo | Lactose | Lattosio | לקטוז | Лактоза | Lactose | ラクトース | Laktoza | Lactose | Лактоза | Laktoosi | Laktos | Laktoz