Saccharide is a very important organic compound in cells. It contains C, H and O, and their ratio is generally 1:2:1. Its chemical formula is written as Cn(H₂O)n. sometimes, so it is also called carbohydrate. But there is an exception, deoxyribose lacks one oxygen atom and its chemical formula is C₅H₁₀O₄. Saccharide is the main energy substance needed for life activities. Some Saccharides are also raw materials for biological macromolecules (proteins and nucleic acids). Saccharides are divided into monosaccharides, oligosaccharides and polysaccharides according to their constituents.
| Monosaccharide | ||
|---|---|---|
| Types | Component | Distribution |
| Glucose | C₆H₁₂O₆ | It is the main energy source for life, and all plant and animal contain glucose. |
| Fructose | C₆H₁₂O₆ | Sweet fruit and honey |
| Galactose | C₆H₁₂O₆ | mammal milk, plant gum, nerve system |
| Disaccharide | ||
| Lactose | Glucose + Galactose | mammal milk |
| Sucrose | Glucose + Fructose | It can store energy in the plant. |
| Maltose | Glucose + Glucose | Plant tissue in which starch hydrolysis occurs |
Monosaccharides
Monosaccharides are the smallest units that make up sugars. The common monosaccharides are glucose, fructose, and galactose. They are all sugars consisting of 6 carbon atoms and are isomers of each other.
Glucose or grape sugar
Glucose was first isolated from raisins or grapes and it is also known as grape sugar. Starch, glycogen and sucrose are all digested into glucose before they can be used by the body. Glucose is the main source of energy needed for cellular life activities. Many plant fruits are rich in glucose.
Fructose or fruit sugar
Fructose is also named fruit sugar. It is a isomer of glucose, where the aldehyde group in glucose is replaced with a ketone group. Fructose is not available to humans directly; it must be converted to glucose in the liver before it can be used to provide energy to cells. It is 1.8 times sweeter than sucrose and is commonly used as a sweetener in the food industry. Some particularly sweet natural foods contain large amounts of fructose, such as pears, lychees and honey.
Galactose
Galactose is an isomer of glucose and they have a different arrangement of hydroxyl groups on the carbon ring. It needs to be converted to glucose in liver before being used by body. It is usually found as a polysaccharide in plant gums or as lactose in mammal milk, or as glycolipids in nervous system..
Disaccharides
Two monosaccharide molecules form a disaccharide through a glycosidic bond. Lactose, sucrose and maltose are all common disaccharides.
Lactose
Lactose is found in mammalian milk and it is composed of glucose and galactose. Lactose is not digested and absorbed in the human stomach and goes directly to the intestine where it is broken down by lactase into glucose and galactose. Galactose is a component of glycolipids that make up brain and nerve tissue and is important for infant intellectual development.
Sucrose
Sucrose is the most common disaccharide, and it is composed of glucose and fructose. Much of glucose formed by photosynthesis is converted to sucrose and stored, making it one of the most abundant sugars in plant tissues. Edible sucrose is mainly obtained from sugar cane and beet.
Maltose
Maltose consists of two glucoses. It is found only in the tissues where starch is hydrolyzed. Maltose is present in large amounts in germinated grains; amylase in saliva hydrolyzes starch into maltose, which is why rice tastes a little sweet when it is chewed.