Lactose is a sugar found in milk, commonly known as ‘milk sugar.’ It is a naturally occurring component that provides energy.
Understanding Lactose
Lactose, commonly known as ‘milk sugar,’ is a type of sugar found in milk and dairy products from mammals, including humans, cows, and goats. Its chemical formula is C12H22O11. Lactose makes up approximately 2% to 8% of milk by mass. This compound is a white, water-soluble solid with a mildly sweet taste. It is formed from two simpler sugar units: glucose and galactose.
Lactose as a Carbohydrate
Macromolecules are large, complex molecules essential for life, built from smaller repeating units. Lactose is classified as a carbohydrate, one of the four main classes of biological macromolecules, alongside proteins, lipids, and nucleic acids. Carbohydrates serve primarily as energy sources for the body.
Carbohydrates are broadly categorized into monosaccharides, disaccharides, and polysaccharides based on the number of sugar units they contain. Monosaccharides are simple sugars, such as glucose or fructose. Disaccharides are formed when two monosaccharides join, like sucrose (glucose + fructose) or maltose (glucose + glucose). Polysaccharides are large chains of many monosaccharide units, examples of which include starch and glycogen.
Lactose is a disaccharide, formed from one molecule of glucose and one molecule of galactose. These two monosaccharides are linked by a specific chemical bond known as a β-1→4 glycosidic linkage.
The Biological Role of Lactose
Lactose is an energy source for infants. Human milk, for instance, contains about 7.2% lactose, providing up to 50% of an infant’s energy requirements.
The breakdown of lactose is facilitated by lactase, an enzyme produced in the small intestine. Lactase breaks down lactose into its two simpler sugars, glucose and galactose, through hydrolysis. These monosaccharides are then absorbed into the bloodstream and utilized by the body for energy.
Galactose derived from lactose also contributes to the synthesis of other macromolecules, such as those found in nerve cell membranes. When there is insufficient lactase enzyme, lactose cannot be properly digested in the small intestine. Undigested lactose then moves into the large intestine, where it is fermented by bacteria. This fermentation can lead to symptoms like bloating, gas, and diarrhea, a condition known as lactose intolerance.