Disaccharide: Definition, Types, Structure, & Examples

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Disaccharide Definition

A carbohydrate is made up of two monosaccharides that, when fully hydrolyzed, release two monosaccharide molecules. Disaccharide is an etymological word that refers to two saccharides. The unit structure of carbohydrates is referred to as a saccharide. A disaccharide, then, is a carbohydrate made up of two saccharides (or two monosaccharide units).

Monosaccharides and disaccharides are both referred to as sugar. Because monosaccharides are the most basic kind of sugar, they are also known as simple sugars. Sucrose is a disaccharide made up of two monosaccharides: glucose and fructose, and is commonly referred to as table sugar or granulated sugar.

What is Disaccharide?

Carbohydrates are organic molecules that are made up of carbon, hydrogen, and oxygen in a 1:2:1 ratio. They are a kind of biomolecule that belongs to one of the most significant categories.

They are a significant energy source. They’re also used as structural elements. They are divided into two categories as nutrients: simple carbs and complex carbohydrates. Simple carbohydrates, often known as sugar, are carbohydrates that are easily digested and provide a quick source of energy.

Complex carbohydrates (such as cellulose, starch, and glycogen) take longer to digest and metabolise than simple carbs. They are generally abundant in fibre and, unlike simple carbs, are less prone to producing blood sugar increases.

Disaccharide Characteristics

Disaccharides, like other carbohydrates, are made up of hydrogen, carbon, and oxygen. The ratio of hydrogen to oxygen atoms in disaccharides is generally 2:1, which is why they’re called carbon hydrates.

Disaccharides have the typical chemical formula C12H22O11. Disaccharides, like other carbohydrates, are organic molecules since they include carbon and C-C and C-H covalent bonds. A disaccharide is a sugar or carbohydrate that consists of two monosaccharides joined together by a glycosidic bond (or glycosidic linkage).

The most basic kind of carbohydrate is monosaccharide. Covalent connections between the hydroxyl groups of two monosaccharides are known as glycosidic bonds. Even if they have the same chemical formula, different types of disaccharides, as well as monosaccharide components, have distinct bond forms and, as a result, varied characteristics.

The number of monosaccharide units that make up disaccharides differs from the number of monosaccharide units that make up oligosaccharides and polysaccharides. Only two monosaccharides make up disaccharides, whereas three to ten monosaccharides make up oligosaccharides. Polysaccharides are made up of multiple monosaccharide units, as the name suggests.

Synthesis of Disaccharide

Dehydration synthesis refers to the chemical process of connecting monosaccharide units that results in the release of water as a byproduct. Disaccharides are made by displacing a hydroxyl radical from one monosaccharide and a proton from the other, and then covalently linking the two monosaccharides together.

The proton (hydrogen ion) and the detached hydroxyl radical combine to create a water molecule. As a result, condensation of two monosaccharides is one technique to make a disaccharide. With the aid of the enzyme disaccharidases, a disaccharide can be hydrolyzed back to its monomeric monosaccharide components (sucrase, lactase, and maltase, for example, are enzymes that degrade sucrose, lactose, and maltose, respectively). While condensation requires the removal of water, hydrolysis includes the use of a water molecule.

Disaccharide Classification

Disaccharides are divided into two main categories: reducing and non-reducing. A disaccharide with a free hemiacetal unit that can act as a reducing aldehyde group is known as a reducing disaccharide. Reducing disaccharides comprise maltose and cellobiose.

Non-reducing disaccharides are disaccharides that do not operate as a reducing agent, as their name indicates. Because they are connected by an acetal linkage between their anomeric centres, neither monosaccharide that makes up the disaccharide has a free hemiacetal unit. Sucrose and trehalose are two examples.

Disaccharide Examples

Disaccharides come in a variety of forms, but the most prevalent are sucrose, lactose, and maltose. Two monosaccharides are linked by a covalent bond in these three. C12H22O11 is the general chemical formula.

Sucrose (common table sugar) is a disaccharide produced when glucose and fructose are combined. The condensation process brings these two monosaccharides together. C-1 (on the glycosyl unit) and C-2 are connected by a glycosidic bond (on the fructosyl unit). Sucrose is digested or broken down into monosaccharide units via hydrolysis, which is accomplished using the enzyme sucrase.

Sucrose is converted to glucose and fructose when the link between the two monosaccharides is broken. Sucrose is harvested from plants such as sugar cane and sugar beet and refined before being sold as table sugar. It’s a sweetening substance that’s utilised in food and drinks.

Lactose (milk sugar) is made up of two sugars: glucose and galactose. C12H22O11 is its chemical formula. Lactose is a naturally occurring sugar found in the milk of animals, including humans. It is derived from bovine and is used to make baby formulae. The lactose content in cow’s milk is around 4.7 percent. Lactose is digested or broken down into monosaccharide units by hydrolysis, which is accomplished by the enzyme lactase.

Lactose is converted to glucose and galactose when the link between the two monosaccharides is broken. Lactose intolerant people are unable to digest or break down lactose. This creates nourishment for the intestinal bacteria that produces gas. This may cause stomach discomfort and flatulence. Lactic acid may be made from lactose. Lactobacilli are microorganisms that can convert lactose to lactic acid, which is utilised in the food industry to make dairy products like yoghurt and cheese.

Maltose (malt sugar) is a reducing disaccharide that results from the joining of two glucose monomers via α(1→4) glycosidic bond. As a result, it may be thought of as the structural unit of glycogen and starch. Maltose is digested or broken down into monosaccharide units with the assistance of the enzyme maltase.

Maltose is converted to two glucose units when the link between the two glucose units is broken. Maltose is a sweetener, a nutrition in baby formula, and a component of bacteriological culture medium. It’s also utilised in baked goods. When carbon dioxide is generated and released during the conversion of starch into maltose by reacting the starch with enzymes, it causes bread dough to rise.

Lactulose, chitobiose, kojibiose, nigerose, isomaltose, sophorose, laminaribiose, gentiobiose, turanose, maltulose, trehalose, palatinose, gentiobiulose, mannobiose, melbiose, mellibiulose, rutinose, rutinulose, xylobiose are the examples.

Biological Importance of Disaccharide

Disaccharides in the diet, like other carbs, are a source of energy. Disaccharides are eaten and digested to produce monosaccharides, which are essential metabolites in the production of ATP. ATPs are chemical energy molecules that are produced in the body through aerobic and anaerobic respiration.

The most prevalent type of monosaccharide used by the cell to generate ATP is glucose, which is phosphorylated at the substrate level (glycolysis) and/or oxidatively phosphorylated (involving redox reactions and chemiosmosis).

A disaccharide-rich diet is one of the sources of glucose. Ordinary table sugar, sucrose, is widely used as a sweetener. It’s utilised in drinks and baked goods like cakes and cookies. The enzyme invertase in the small intestine breaks down sucrose into glucose and fructose when it is ingested.

However, too much fructose might cause malabsorption in the small intestine. Unabsorbed fructose transferred to the large intestine might be fermented by the colonic flora if this happens. This might cause stomach pains, diarrhoea, flatulence, and bloating.

Too much glucose can also be harmful to one’s health. Sugar consumption that is excessive can result in diabetes, obesity, tooth decay, and cardiovascular disease. Lactose, a disaccharide present in breast milk, is given to newborns as a nutritional source.

Lactobacilli are microorganisms that can convert lactose to lactic acid, which is utilised in the food industry to make dairy products like yoghurt and cheese. Although maltose is less sweet than sucrose, it can be used as a sweetener.

Disaccharides, particularly sucrose, are formed by vascular plants as a source of nutrition that is delivered to various sections of the plant via the phloem tissues. Sugarcane, in particular, is collected for commercial sugar production.

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