Lactose.html |
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Contents |
Main
| Lactose | |
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| IUPAC name | (2S,3R,4R,5S,6R)-6- (hydroxymethyl)-5-((2S,3R,4S,5R,6R)- 3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro- 2H-pyran-2-yloxy)tetrahydro-2H-pyran-2,3,4-triol |
| Other names | Milk Sugar |
| Identifiers | |
| CAS number | 63-42-3 |
| Properties | |
| Molecular formula | C12H22O11 |
| Molar mass | 342.29648 g/mol |
| Appearance | white solid |
| Solubility in water | 0.216 g/mL |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Lactose (also referred to as milk sugar) is a sugar that is found most notably in milk. Lactose makes up around 2–8% of milk (by weight). The name comes from the Latin word for milk, plus the -ose ending used to name sugars. Its systematic name is β-D-galactopyranosyl-(1↔4)β-D-glucopyranose.
Chemistry
Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose fragments bonded through a β1-4 glycosidic linkage.
Solubility
Lactose has a solubility of 1 in 4.63 measured %w/v. This translates to 0.216 g of lactose dissolving readily in 1 mL of water.
The solubility of lactose in water is 18.9049 g at 25°C, 25.1484 g at 40°C and 37.2149 g at 60°C per 100 g solution. Its solubility in ethanol is 0.0111 g at 40°C and 0.0270 g at 60°C per 100 g solution.1
Digestion of Lactose (Catabolism)
Infant mammals are fed on milk by their mothers, which is rich in the carbohydrate Lactose. To digest it, an enzyme called lactase (β-D-galactosidase) is secreted by the intestinal villi. This enzyme cleaves the lactose molecule into its two subunits; glucose and galactose for absorption.
Since lactose occurs mostly in milk, in most mammals the production of its digestive enzyme, lactase, gradually decreases with maturity, due to lack of constant consumption.
Many people who live in Europe, the Middle East, India, and parts of East Africa, maintain normal lactase production into adulthood. In many of these areas, milk from mammals such as cattle, goats, and sheep is used as a large source of food. Hence, it was in these regions that genes for lifelong lactase production first evolved. The genes of lactose tolerance have evolved independently in various ethnic groups. 2
Production of Lactose (Anabolism)
Lactose is produced (an anabolic pathway) in the mammary glands during lactation. Lactose is formed when galactose and glucose bind each other. The reaction first starts with two glucose molecules. One of them is converted to an active glucose molecule (UDP-glucose). The UDP-glucose is converted to UDP-galactose by the enzyme UDP-glucose 4-epimerase. The UDP-galactose is then added to the other glucose (by the enzyme galactosyltransferase) to form the disaccharide lactose.
References
- ^ Machado, José J.B.; João A. Coutinho, Eugénia A. Macedo (2000). Solid–liquid equilibrium of a-lactose in ethanol/water, Fluid Phase Equilibria, http://path.web.ua.pt/file/FPE%20(2000)%20173%20121.pdf. Retrieved on 5 December 2007.
- ^ People who are not tolerant may suffer uncomfortable and/or socially unacceptable symptoms of too much lactose consumption. basically, lactose is not broken down and provides food for gas producing gut flora. This leads to bloating, and flatulence and perhaps GI upset. Nicholas Wade (December 10, 2006). "Study Detects Recent Instance of Human Evolution", The New York Times. Retrieved on 5 December 2007.
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