biological importance of disaccharides?
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Biology Dictionary
Disaccharide
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Disaccharide Definition
A disaccharide, also called a double sugar, is a molecule formed by two monosaccharides, or simple sugars. Three common disaccharides are sucrose, maltose, and lactose. They have 12 carbon atoms, and their chemical formula is C12H22O11. Other, less common disaccharides include lactulose, trehalose, and cellobiose. Disaccharides are formed through dehydration reactions in which a total of one water molecule is removed from the two monosaccharides.
Functions of Disaccharides
Disaccharides are carbohydrates found in many foods and are often added as sweeteners. Sucrose, for example, is table sugar, and it is the most common disaccharide that humans eat. It is also found in other foods like beetroot. When disaccharides like sucrose are digested, they are broken down into their simple sugars and used for energy. Lactose is found in breast milk and provides nutrition for infants. Maltose is a sweetener that is often found in chocolates and other candies.
Plants store energy in the form of disaccharides like sucrose and it is also used for transporting nutrients in the phloem. Since it is an energy storage source, many plants such as sugar cane are high in sucrose. Trehalose is used for transport in some algae and fungi. Plants also store energy in polysaccharides, which are many monosaccharides put together. Starch is the most common polysaccharide used for storage in plants, and it is broken down into maltose. Plants also use disaccharides to transport monosaccharides like glucose, fructose, and galactose between cells. Packaging monosaccharides into disaccharides makes the molecules less likely to break down during transport.
Formation and Breakdown of Disaccharides
When disaccharides are formed from monosaccharides, an -OH (hydroxyl) group is removed from one molecule and an H (hydrogen) is removed from the other. Glycosidic bonds are formed to join the molecules; these are covalent bonds between a carbohydrate molecule and another group (which does not necessarily need to be another carbohydrate). The H and -OH that were removed from the two monosaccharides join together to form a water molecule, H2O. For this reason, the process of forming a disaccharide from two monosaccharides is called a dehydration reaction or condensation reaction.
When disaccharides are broken down into their monosaccharide components via enzymes, a water molecule is added. This process is called hydrolysis. It should not be confused with the process of dissolution, which happens when sugar is dissolved in water, for example. The sugar molecules themselves do not change structure when they are dissolved. The solid sugar simply turns into liquid and becomes a solute, or a dissolved component of a solution.
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