Carbohydrates play a variety of functions in nature. Because of this, they are indispensable elements for living beings. The main functions of carbohydrates are:
- Metabolic fuel – various monosaccharides may be used as a source of chemical energy through its catabolism. Logically, the main carbohydrate used as metabolic fuel is glucose. However, there are several other monosaccharides that can also be used as metabolic fuel (more information on this subject here), such as fructose, mannose or galactose;
- Nucleotide components– this function is performed by two different pentose, ribose and deoxyribose. Actually, only one of these carbohydrates is a “pure” monosaccharide (ribose), the other is a derivative of monosaccharide (deoxyribose). Soon, I will write a post about this... Both ribose and deoxyribose are pentoses, that means, they are monosaccharides with 5 carbons. Ribose enters in the composition of ribonucleotides (and consequently RNA) while deoxyribose takes part of the composition of deoxyribonucleotides (and hence the DNA);
- Metabolic fuel reserve - some polysaccharides play the function of metabolic fuel reserve. In this context, there are two molecules that deserve a highlight: starch and glycogen. Both are composed of a single type of monosaccharide, glucose. Starch is the reserve polysaccharide of glucose in plant cells, while glycogen is the reserve polysaccharide in animal cells;
- Protection - some polysaccharides play a protective function, such as chitin, which is the main component of the exoskeleton of insects;
- Lubrication and hydration - due to their rich composition in hydrophilic functional groups, carbohydrates have the ability to interact with a large number of water molecules. Because of this feature, various polysaccharides form viscous and highly hydrated mixtures. These polysaccharides are referred to as glycosaminoglycans and are essential for the skin, joints, etc.
- Recognition and cell adhesion - there are several molecules involved in cell adhesion and recognition. These molecules are found on the cell surface and have carbohydrate components, being called glycoproteins or glycolipids.