Isabella Carter
Lactose is a disaccharide sugar molecule, which is composed of two monomers: galactose and glucose. It is commonly found in milk and has a mildly sweet taste. The molecule is formed when one molecule of galactose and one molecule of glucose join through a dehydration reaction, resulting in a glycosidic linkage. This process involves the removal of a water molecule, leaving a disaccharide molecule with the chemical formula C12H22O11. Lactose needs to be broken down into its constituent monomers by an enzyme called lactase before it can be absorbed in the gut.
| Characteristics | Values |
|---|---|
| Number of Monomers | 2 |
| Type of Monomers | Glucose and Galactose |
| Molecular Formula | C12H22O11 |
| Percentage Composition in Milk | 2-8% |
| Sweetness Relative to Sucrose | 0.2-0.4 |
| Caloric Value | 2-4 kcal/g |
| Glycemic Index | 46-65 |
| Solubility | Soluble in Water |
| Colour | White |
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What You'll Learn
Lactose is a disaccharide composed of galactose and glucose
Lactose is a disaccharide, a type of carbohydrate formed when two monosaccharides (simple sugars) are joined by a glycosidic linkage. The two monomers that constitute a molecule of lactose are galactose and glucose.
Lactose is found naturally in milk, making up around 2-8% of its mass. Infant mammals nurse on their mother's milk, which is rich in lactose. The intestinal villi secrete the enzyme lactase (β-D-galactosidase) to digest lactose. This enzyme breaks down the lactose molecule into its two subunits, the simple sugars glucose and galactose, which can then be absorbed.
In most mammals, the production of lactase decreases with maturity due to weaning, as lactose is removed from the diet. However, in some ethnic groups, such as those with ancestry in Europe, West Asia, and South Asia, the genes for lifelong lactase production have evolved, allowing them to digest lactose as adults.
Lactose has a mildly sweet taste and is used in the food industry. It can be hydrolysed to glucose and galactose, isomerised in an alkaline solution to lactulose, and catalytically hydrogenated to lactitol, a polyhydric alcohol used to treat constipation.
The molecular formula for lactose is C12H22O11, and its systematic name is β-D-galactopyranosyl-(1→4)-D-glucose. The glucose can be in either the α-pyranose or β-pyranose form, while the galactose can only take the β-pyranose form.
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Glucose and galactose are monosaccharides
Lactose is a disaccharide, which means it is formed when two monosaccharides (simple sugars) join through a process called a condensation reaction or dehydration synthesis reaction. This reaction involves the removal of a water molecule from the functional groups of the monosaccharides.
The two monomers that constitute a molecule of lactose are glucose and galactose, which are both monosaccharides. Glucose is a simple sugar that is vital for cellular energy in both plants and animals. It is a product of photosynthesis in plants and is stored as starch, which can be broken down into glucose by humans and animals. Glucose is also the sugar that forms the structure of cellulose, which is the main component of plant cell walls and provides structural support. Galactose, on the other hand, is a monosaccharide that is absorbed directly by intestinal cells without further breakdown.
The enzyme lactase, found in the intestinal walls, is responsible for breaking down lactose into its constituent monosaccharides, glucose and galactose. This process is necessary for the absorption of lactose in the gut. Individuals who are lactose intolerant lack this enzyme, leading to an inability to digest lactose and resulting in symptoms such as diarrhea, bloating, and flatulence.
Lactose is commonly found in milk, constituting around 2-8% of its mass. The sweetness of lactose is relatively mild, ranging from 0.2 to 0.4 compared to 1.0 for sucrose. The caloric value of lactose can vary depending on factors such as ingested dose and lactase activity, typically ranging from 2 to 4 kcal/g.
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Lactose has the molecular formula C12H22O11
Lactose is a disaccharide, which is a type of carbohydrate. It is composed of two monomers: galactose and glucose. These monomers are simple sugars that are joined by a glycosidic bond to form lactose. This process is known as a dehydration reaction, where a water molecule is lost. The molecular formula of lactose, C12H22O11, reflects the number of atoms of each element in a molecule of lactose. Specifically, it indicates that each molecule contains 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms.
Lactose is commonly found in milk, constituting around 2-8% of milk by mass. It is a naturally occurring sugar that gives milk a mildly sweet taste. The name "lactose" derives from the Latin word "lact," meaning milk, and the suffix "-ose," used to denote sugars.
The enzyme lactase is responsible for breaking down lactose into its constituent monomers, galactose and glucose. This process occurs in the small intestine, where lactase is secreted by intestinal villi or found on intestinal walls. Once broken down, the simple sugars galactose and glucose can be easily absorbed by the body.
Not everyone produces lactase, and the ability to produce it varies among different populations. Many people of European, West Asian, South Asian, and African descent maintain lactase production into adulthood due to genetic adaptations. In contrast, lactose intolerance is more prevalent in people from East Asian, South-East Asian, and Oceanian populations, where lactase production decreases with maturity.
Lactose intolerance occurs when the body does not produce lactase, leading to an inability to digest lactose. Undigested lactose then becomes food for gut flora, resulting in gastrointestinal symptoms such as diarrhea, bloating, and flatulence. However, undigested lactose acts as dietary fibre and positively affects the absorption of minerals like calcium and magnesium.
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Lactose is hydrolysed to glucose and galactose
Lactose is a disaccharide, a type of carbohydrate, composed of two monomers: galactose and glucose. These monomers are simple sugars that are joined by a glycosidic linkage, forming a β-1→4 glycosidic bond to be specific. This bond is created through a dehydration reaction, where a water molecule is lost. The molecular formula of lactose is C12H22O11.
Lactose is found naturally in milk, constituting around 2-8% of milk by weight. It is also produced industrially as a by-product of the dairy industry, through the purification of whey or milk plasma. Whey is the liquid remaining after milk is curdled and strained, such as in cheese production, and it contains high levels of lactose.
Lactose needs to be broken down into its constituent monosaccharides, galactose and glucose, before it can be absorbed by the body. This breakdown occurs in the small intestine with the help of the enzyme lactase (β-D-galactosidase). Lactase is secreted by intestinal villi and breaks the glycosidic bond in the lactose molecule, hydrolysing it into its monomers. This process is vital for the absorption of lactose as galactose and glucose can be directly absorbed by intestinal cells.
Some individuals are lactose intolerant, meaning they do not produce the lactase enzyme. In these cases, lactose is not broken down and instead becomes food for gas-producing gut flora, leading to gastrointestinal symptoms such as diarrhoea, bloating, and flatulence. However, even in lactose-intolerant individuals, the absorption of separate galactose and glucose is not an issue, as these monomers do not require further breakdown.
The hydrolysis of lactose to glucose and galactose is not only important for digestion but also has commercial applications. For example, lactose can be isomerised in an alkaline solution to produce lactulose, a treatment for constipation, or catalytically hydrogenated to create lactitol, a polyhydric alcohol.
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Lactose intolerance is caused by a lack of the enzyme lactase
Lactose is a disaccharide, which means it is composed of two monomers: the simple sugars glucose and galactose. It is found naturally in milk and makes up around 2-8% of milk by weight. Lactose has a mildly sweet taste and is used in the food industry.
Lactose intolerance is the inability to digest lactose. This is caused by a lack of the enzyme lactase, which is usually produced in the small intestine and turns milk sugar into glucose and galactose, which are then absorbed into the bloodstream. If there is not enough lactase, the lactose moves into the colon, where it interacts with bacteria, causing the symptoms of lactose intolerance. These symptoms include diarrhea, gas, bloating, abdominal pain, and nausea.
Lactose intolerance is usually harmless but can be uncomfortable. It is most common in people of African, Asian, Hispanic, and Native American descent. The ability to produce lactase into adulthood depends on variants in the regulatory element within the MCM6 gene, which are inherited from parents. People of Northern European descent are more likely to have the variants that promote lactase production, while other populations have a lower prevalence of lactose intolerance due to a long history of dependence on unfermented milk products.
Primary lactose intolerance, the most common type, occurs when people gradually stop producing lactase as they grow out of infancy. Congenital lactase deficiency, on the other hand, is a rare genetic disorder that causes lactose intolerance from birth. This is caused by variants or mutations in the LCT gene, which interfere with the processing and function of lactase.
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Frequently asked questions
Lactose is a disaccharide composed of the monomers galactose and glucose.
Monomers are simple sugars that are linked by glycosidic bonds to form disaccharides and polysaccharides.
A disaccharide is a type of carbohydrate formed when two monosaccharides (simple sugars) are joined by a glycosidic linkage.
Common disaccharides include lactose, maltose, and sucrose. Lactose is found naturally in milk and is composed of galactose and glucose monomers. Maltose is formed by the dehydration reaction between two glucose molecules, and sucrose is composed of glucose and fructose monomers.
Lactose is the natural sugar found in milk and makes up around 2-8% of its composition. It has a mildly sweet taste and is used in the food industry. Lactose can be broken down into its constituent monomers, galactose and glucose, by the enzyme lactase, which is secreted by infant mammals to digest milk.
