Tuesday, June 12, 2012

Classification of carbohydrates with examples

Classification of carbohydrates with examples

What are carbohydrates?
Carbohydrates are organic compounds made up of the elements or components carbon, hydrogen, and oxygen. The hydrogen and oxygen atoms are present in the ratio 2:1. The general formula for carbohydrates is CnH2mOm.

Foods containing carbohydrates come mainly from plants and are a good source of energy for the body. There are three main groups of carbohydrates: monosaccharide, disaccharides, and polysaccharides.

Monosaccharide or single sugar
There are many single sugars or monosaccharide. The most common single sugar are the sugars with six carbon atoms – glucose, fructose, and galactose. Glucose is found in all animals, at least in small quantities. Fructose is found in plants, but rare in animals. Galactose is found in milk sugar from mammals. Glucose, fructose, and galactose have the same general formula C6H12O6, but their atoms are arranged differently within the molecules. These different arrangements give the sugars different chemical and biological properties.

Disaccharides or double sugars
Double sugars are so called because each molecule of a double sugar is made up of two molecules of single sugars bonded together. Double sugars are also called disaccharides. Disaccharides have the general formula C12H22O11. However, their atoms have different arrangements within the molecules. Common disaccharides are maltose, sucrose, and lactose.
  • Maltose = glucose + glucose. Maltose occurs in sprouting grains.
  • Sucrose = glucose + fructose. Sucrose occurs in sugarcane stems, sweet fruits, and certain storage roots, for example, carrots.
  • Lactose = glucose + galactose. Lactose occurs in the milk of all mammals, including humans.

Polysaccharides or complex carbohydrates
Polysaccharides consist of many monosaccharide molecules joined together. Starch, glycogen, and cellulose are complex carbohydrates. Plants store glucose in the form of starch. In animals and fungi, the main store of glucose is glycogen. Cellulose forms the main parts of the cell walls of plants. Starch, glycogen, and cellulose are each made up of numerous glucose molecules condensed together, but the glucose molecules are linked together and arranged in different ways. Hence, starch, glycogen, and cellulose have different properties.

What are the functions of carbohydrates?
Carbohydrates are needed:
- As a substrate for respiration, to provide energy for cell activities.
- To form supporting structures, for example, cell walls in plants.
- To be converted into other organic compounds such as amino acids and fats.
- For the formation of nucleic acids, for example, DNA.
- To synthesize lubricants, for example, mucus which consists of a carbohydrate and a protein.
- To synthesize the nectar in some flowers. Nectar is a sweet liquid that plants produce to attract insects.
