Carbohydrates
Carbohydrates are molecules that contain carbon, hydrogen and oxygen (and sometimes sulphur and nitrogen). They are extremely important for life since they are used for storing and transporting energy. To learn how to test for them see tests.
Monosaccharides
These are the simplest form of carbohydrates, being made of only one sugar; and often have a sweet taste. An example of a monsaccharide you may remember from previous study is glucose. It has the formula C6H12O6 and the following structure:
Glucose consists of a ring of 5 carbon and an oxygen atom around which is a series of H, OH and a CH2OH. The strcuture can be simplified to a polygon where each point represents a carbon.
Fructose has the same formula as glucose but a different structure, consisting of a 4 carbon 1 oxygen ring. For this reason it is said to be an isomer of glucose, and has the following structure.
Disaccharide
A disaccharide is made up of two monosacharides and has the general formula Cn(H2O)n-1. Examples of them include maltose and sucrose. But before we look at them, let's take a look at how disacharides are formed.
In the condensation reaction an OH from one of the monosaccharides and H from the other are removed to produce water. Leaving an Oxygen atom that acts as the bond between the two molecules. This is known as a glycosidic bond. The breaking up of a disacharide is a hydrolysis reaction and involves the addition of water. Maltose and sucrose are composed as follows.
Maltose = Glucose + Glucose
Sucrose = Glucose + Fructose
Polysaccharide
A polysaccharide is a carbohydrate polymer where the monomers (single units) are monosaccharides. The monomers are joined by glycosidic links, they tend to be insoluble (do not dissolve) and have a very dull taste.
Examples of polysaccharides are starch and glycogen, both made of glucose but arranged slightly differently. The picture below is a simple representation to help you understand the structure of a polysaccharide.
Uses
As mentioned in the introduction, carbohydrates are extremely important in life, and in the table below are just a few examples of the fundamental uses of carbohydrates.
| Use | Type of Carbohydrate | Example |
|---|---|---|
| Respiration | Monosaccharide | Glucose |
| Component in RNA and DNA | Monosaccharide | Ribose and Deoxyribose |
| Building cell walls | Polysaccharide | Cellulose or Murecin |
| Energy storage | Polysaccharide | Starch or glycogen |
| Sweeting your food (table sugar) | Disaccharide | Sucrose |