is a
Disaccharide that 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 C
12H
22O
11 and its molecular weight is 342.3. In the young of mammals, an
Enzyme called
Lactase is secreted by the intestinal villi, and this enzyme cleaves the molecule into its two subunits for absorption.
The polysaccharides of Lactose consist of β-D-galactose and α-D-glucose molecules bonded through β1-4 glycosidic linkage.
Normally, as the young grow up, production of lactase gradually ceases, and they are then unable to metabolise lactose. This is perhaps an evolutionary 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 ,
Goat s and
Water Buffalo . The process of retaining infant characteristics into adulthood is one of the simplest routes of evolutionary 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 .
