As the name carbohydrate implies, these compounds contain the elements carbon, hydrogen and oxygen according to the general formula where in may be any number. The carbohydrates are extremely important components of living matter.
In addition to constituting the major fuel substances in living systems, they play an important structural role especially in plants. Although there are carbohydrates whose molecules contain three, four, or five carbon atoms, the most common macromolecules are the six-carbon sugars railed monosaccharides.
It is from these six-carbon macromolecules that the complex macromolecules are built. Conversely, in a living system, the large polysaccharides must be broken down into the smaller monosaccharides in order to be utilized.
In the process of building the macromolecular polysaccharides from the macromolecular monosaccharide’s, and in the decomposition of polysaccharides to monosaccharides, intermediate carbohydrate units called oligosaccharides, trasaccharides, and disaccharides are formed. The prefix outgo means “a few” and describes a carbohydrate containing few or several monosaccharide units joined together.
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Glucose is by far the most abundant monosaccharide in nature, that is, it is the most common macromolecular carbohydrate unit used as fuel by living cells. Fructose and galactose may also be used as fuel for cells; in fact: when glucose if broken down in living systems, it is changed to a form of fructose. In addition to its function as a fuel substance, ribose is one constituent of the nucleic acids.
It should be understood, or course, that other micro molecules may be involved in a similar fashion. Under certain conditions, two glucose units may bond together to from the disaccharide maltose. Notice that in this water is shown as being removed during the reaction and adjacent carbons are bonded by an oxygen atom.
In a similar fashion, another glucose unit may be added to form a disaccharide. The addition of still others would form an oligosaccharide, and finally, a large macromolecular polysaccharide would result. This very Process occurs in many animals when the polysaccharide glycogen is formed and stored; in plants, the multiplication of glucose unit’s produces starch as polysaccharide.
A reversal of the process just illustrated results in the breakdown of glycogen and starch to their component glucose molecules. This occurs in plant and animal digestion, for example, when the 1-4 carbon linkages are broken through enzymatic action and a molecule of water is split and added to each linkage site.