(Biochemistry of Carbohydrates: Introduction, Properties, Classification and Biological Significance)
Carbohydrates are polyhydroxy aldehydes or ketones
Carbohydrates are the most abundant bio-macro-molecules on the earth. They are commonly known as sugars because most of them have a sweet taste. Chemically all carbohydrates are polyhydroxy (contain many hydroxyl, – OH, groups) aldehydes or ketones. All carbohydrates are hydrates of carbon and they contain C, H and O. The ratio of hydrogen and oxygen in the majority of carbohydrates will be in 2:1 as in water. Some carbohydrates also contain nitrogen, phosphorous and sulfur. Majority of carbohydrates, not all, have the empirical formula (CH2O)n. In biochemistry, carbohydrates are denoted as saccharides. The term saccharide is derived from a Greek word ‘sakkharon’ meaning sugar.
Green plants fix the energy of sunlight by photosynthesis. In photosynthesis, the light energy is converted into the chemical energy and it is stored in some carbohydrates such as glucose, fructose, sucrose, starch etc. The oxidative breakdown of these carbohydrates by respiration release the energy stored in them and this energy is utilized for the various metabolic activities of the cells.