The main function of carbohydrates in animals is to provide an energy source. A few carbohydrates serve as structural units such as deoxyribose. This sugar can be found in DNA. When the energy is not being used by the animal, the carbohydrate is stored as glycogen. Carbohydrates are composed of carbon, oxygen, and hydrogen. In most carbohydrates, there is one carbon atom for each water molecule. Carbohydrates are categorized into three groups based on molecule size.
Monosaccharides are composed of three to seven carbons. Prefixes indicate the number of carbon atoms contained in the molecule. For example, a pentose would consist of five carbon atoms. One of the main energy suppliers to the body happens to be a monosaccharide called glucose, a hexose.
A disaccharide is the result when two monosaccharides combine by dehydration synthesis. One water molecule also results as a byproduct. For example, the monosaccharides fructose and glucose combine in the chemical equation C6H12O6(glucose) + C6H12O6(fructose) ----> C12H22O11(sucrose) + H2O(water) to form sucrose and water. You may notice that glucose and fructose have the same chemical composition; however they differ in the relative positions of their carbon and oxygen atoms. In order to obtain monosaccharides from a disaccharide, all you need to do is add water. This is a process called hydrolysis.
Polysaccharides consist of not only three or four monosaccharides, but tens and hundreds in long chains. These monosaccharides were also joined by dehydration synthesis. The main polysaccharide that is in the human body is glycogen. Glycogen is stored in the liver and skeletal muscles and can be broken down into monosaccharides for use as energy. In order to achieve monosaccharide status, polysaccharides must also go through hydrolysis.