The name carbohydrates indicate that they are hydrates of carbon and contain carbon, hydrogen, and oxygen. Carbohydrates or saccharides are essential components of all living organisms and are, in fact, the most abundant class of all biological molecules. The name carbohydrates, which literally means “carbon hydrate” stems from their chemical composition which is roughly (CH2O)n. These also are defined chemically as aldehyde or ketone derivatives of the higher polyhydric alcohols or compounds which yield these derivatives on hydrolysis.
- The biological significance of carbohydrates
Carbohydrates are of great importance to plants as well as to animals and human beings. Carbohydrates are the structural materials of plants, for example, cellulose is found in plant fibres and in wood. They are widespread and act as reserve materials in tubers, grains and roots. Sucrose is present in the nectar of flowers, in roots, and in fruits. Glucose, fructose, and simple sugars are also found in small amounts in plants as reserve food materials. The carbohydrates such as starches and sugars are the main food for human beings. They are easily digestible and are easily oxidized to provide energy for various physiological processes. These are present in cereals. The carbohydrate derivatives such as glucosides, form important drugs and other medicines for various diseases. The carbohydrates, particularly cellulose and its derivatives are used in the production of artificial silk, paper, plastics, cinema films and explosives. All animal tissues, blood, milk and tissue fluids contain carbohydrates and their derivatives as important constituents, e.g. blood contains glucose as sugar. Muscles and other tissues remove glucose from the blood and form glycogen which provides energy for oxidation. Many tissues are formed by combinations of sugars or sugar derivatives and proteins.
- Aldose—The monosaccharides containing the aldehydic group as the functional groups are called aldoses. They are classified according to the number of carbon atoms present. Aldoses containing three to seven carbon atoms are called Trioses, Tetroses, Pentoses, Hexoses and Heptoses respectively.
- Ketoses—These are the monosaccharides, which contain the ketone group as the functional group. These are also classified according to the number of carbon atoms in them as trioses, tetroses, hexoses and heptoses.