Disaccharide: Definition, Function, and Examples

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Disaccharide Definition

A disaccharide, often known as a double sugar, is a molecule made up of two monosaccharides (simple sugars) joined together. Sucrose, maltose, and lactose are three prevalent disaccharides. They are made up of 12 carbon atoms and have the chemical formula C₁₂H₂₂O₁₁.

Lactulose, trehalose, and cellobiose are some of the less frequent disaccharides. Disaccharides are produced when one water molecule is removed from each of the two monosaccharides in a dehydration process.

Disaccharide Functions

Disaccharides are a kind of carbohydrate that may be found in a variety of foods and are frequently used as sweeteners. Sucrose, for instance, is table sugar and the most common disaccharide consumed by humans. It can also be present in foods like beets.

Disaccharides, such as sucrose, are broken down into simple sugars and utilised for energy when they are digested. Breast milk contains lactose, which gives nourishment to babies. Maltose is a sweetener often found in chocolates and other confections.

Disaccharides like sucrose are utilised by plants to store energy and transfer nutrients through the phloem. Many plants, such as sugar cane, are rich in sucrose because it is an energy storage source. In certain algae and fungi, trehalose is utilised for transport.

Polysaccharides, which are made up of multiple monosaccharides, are also used by plants to store energy. Starch, which is broken down into maltose, is the most prevalent polysaccharide utilised for storage in plants.

In addition, monosaccharides including glucose, fructose, and galactose are also transported between cells by disaccharides in plants. Monosaccharides are packaged into disaccharides to make them less prone to break down during transit.

Formation and Breakdown of Disaccharides

An -OH (hydroxyl) group is removed from one molecule and a H (hydrogen) is removed from the other when disaccharides are created from monosaccharides. To connect the molecules, glycosidic bonds are created; these are covalent bonds between a carbohydrate molecule and another group (which does not necessarily need to be another carbohydrate).

The H and -OH from the two monosaccharides combine to produce H₂O, which is a water molecule. As a result, the formation of a disaccharide from two monosaccharides is referred to as a dehydration or condensation reaction.

A water molecule is added when disaccharides are broken down into their monosaccharide components by enzymes. This is referred to as hydrolysis. It’s not to be confused with the dissolution process, which occurs when sugar dissolves in water, for example.

When sugar molecules are dissolved, their structure does not change. The solid sugar becomes a solute, or a dissolved component of a solution, when it transforms into a liquid.

Disaccharide Examples

i. Sucrose

Sucrose is a disaccharide present in many plants and is widely known as table sugar in its refined form. It is composed primarily of glucose and fructose monosaccharides. Sucrose is a highly significant component of the human diet as a sweetener in the form of sugar.

Sugar cane was initially extracted and refined in India during the eighth century BCE. In reality, the term candy is derived in part from the Sanskrit word khanda, which means sugar crystals. Each year, around 175 metric tonnes of sugar are produced.

Because they lack the enzyme sucrose-isomaltase, people with congenital sucrase-isomaltase deficiency (CSID) are sucrose intolerant and cannot digest it properly. Some patients with CSID also have difficulty digesting starches.

Sucrose intolerance necessitates limiting sucrose intake as much as possible, and may necessitate the use of supplements or medicines.

ii. Maltose

Maltose is made up of two glucose molecules and is also known as malt sugar. Malt is a component of beer, starchy meals like cereal, pasta, and potatoes, and many sweetened processed goods. It is created when grains soften and grow in water.

Maltose is created in plants when starch is broken down for nourishment. It is required for the growth of germinating seeds.

iii. Lactose

Lactose is made up of two sugars: galactose and glucose. Lactose is abundant in mammalian milk, which gives nutrition to newborns. Most mammals can only digest lactose as newborns, and as they get older, they lose this capacity.

Adult individuals with the ability to digest dairy products have a genetic mutation that permits them to do so. This is why so many individuals are lactose intolerant; humans, like other mammals, did not have the capacity to digest lactose through childhood until about 10,000 years ago, when a mutation appeared in some groups.

Intolérance to lactose now exists in a wide range of populations, ranging from ten percent in Northern Europe to ninety percent in areas of Africa and Asia. The quantity of dairy consumed in different cultures’ traditional meals reflects this.

iv. Trehalose

Trehalose, like maltose, is made up of two glucose molecules joined together in a distinct way. Certain plants, fungi, and animals, such as shrimp and insects, contain it. Trehalose is the sugar found in the blood of many insects, including bees, grasshoppers, and butterflies. They utilise it as a storage molecule that, when broken down, provides quick energy for flight.

v. Lactulose

Fructose and galactose combine to produce lactulose. It’s used to treat constipation and liver illness, as well as to check for bacterial overgrowth in the small intestine. It is used in food in certain countries, but it is not authorised in the United States since it is considered a medication that might damage diabetics.

vi. Cellobiose

Cellobiose is made up of two glucose molecules, like maltose and trehalose, but they are connected in a different way. It has been discovered that the primary component of plant cell walls, cellulose, has been hydrolyzed. In bacteriology, the study of bacteria, cellobiose is utilised to perform chemical studies.

vii. Chitobiose

Chitobiose is made up of two glucosamine molecules that are bonded together. It is structurally identical to cellobiose, with the exception that it includes a N-acetylamino group instead of a hydroxyl group. It’s present in some bacteria and is utilised in biochemistry studies to figure out how active enzymes are.

It’s also present in fungus cell walls, insect exoskeletons, arthropod exoskeletons, and crustacean exoskeletons, as well as fish and cephalopods like octopuses and squid.

Disaccharide FAQ

Carbohydrate is an organic molecule made up of carbon, hydrogen, and oxygen in a 2:1 hydrogen:oxygen ratio.

Glucose is a monosaccharide that is present in the blood of mammals and produced by plants during photosynthesis.

A disaccharide is formed when two monosaccharides combine to produce a disaccharide.

Starch is a long chain of glucose generated by plants for energy storage, and it’s found in most people’s meals.

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Disaccharide Citations

Disaccharide digestion and maldigestion. Scand J Gastroenterol Suppl . 1996;216:111-21.
Expedient Synthesis of Core Disaccharide Building Blocks from Natural Polysaccharides for Heparan Sulfate Oligosaccharide Assembly. Angew Chem Int Ed Engl . 2019 Dec 16;58(51):18577-18583.
Disaccharide intolerance. Pediatr Clin North Am . 1967 Feb;14(1):93-107.

Disaccharide – NotesBard