Simple organic molecules present in living material include monosaccharides, amino acids, fatty acids, glycerol and aromatic bases, such molecules are termed monomers. These monomers act as building blocks for the synthesis of larger macromolecules, called polymers, by condensation reactions.
In this essay I shall discuss the above monomers, the polymers they make up and the functions/role of these polymers.
Firstly I will consider monosaccharides. Glucose, fructose and galactose are all monosaccharides termed "simple sugars". Each has the chemical formula C6H12O6, but the arrangement of atoms and chemical groups in them is different. Monosaccharides are classified according to the number of carbon atoms they possess. Monosaccharides that have 3 carbons are termed trioses. E.g. glyceraldehyde and dihydroxyacetone, (used in respiration). Monosaccharides with 5 carbon atoms are called pentoses. E.g. ribose, (involved in the synthesis of nucleic acid, coenzymes and ATP. 6 carbon monosaccharides are termed hexoses. E.g. glucose and fructose, (major sources of energy; involved in the synthesis of polysaccharides). .
Pentose and hexoses are the most common monosaccarhides and exist as chain or ring structures. The 5 membered pentose ring is called a furanose ring and the 6 membered hexose ring is called a pyranose ring.
When 2 monosaccharides are joined by means of a condensation reaction they form a disaccharide. (See diagram below).
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Polysaccharides (e.g. starch, glycogen, cellulose) are formed when large numbers of monosaccharides are joined together in long chains. They provide structural support in plants or at as food and energy stores, e.g. starch in plants and glycogen in animals. They are relatively insoluble in water and have no osmotic effect within the cell.
Starch is composed of amylase, a straight chain of several thousand glucose residues, and amylopectin, a larger branched structure containing many more glucose residues.
