Scientific Definition of Carbohydrates

Carbohydrates Definition

A definition of carbohydrates involves a little basic chemistry. As we will see, there’s more to sugar than meets the eye. If we thought the genome was complex, wait till we meet the sugar family, or glycome.

The genome is child’s play compared to the glycome. “Glycome” is a word coined to refer to the entire spectrum of all saccharide structures and its size and complexity is immense. “Saccharide” is just a more scientific word for sugar.

The simplest carbohydrates are called monosaccharides (Mono = single; saccharide = sugar) of which glucose (blood sugar) is the most well known; others include fructose, galactose, xylose and ribose. These and other monosaccharides are the basic units of carbohydrates.

Definition of Carbohydrates through Organic Chemistry

The definition of carbohydrates gets us into the chemistry of three elements; hydrogen, oxygen and carbon. Consider the word “carbohydrate”.

When two hydrogen atoms and an oxygen atom are combined we get water, very often called a hydrate. So if we then combine a carbon atom with a hydrate, we have a carbohydrate. How simple can it get?

Next, the way that different numbers of atoms of hydrogen, carbon and oxygen connect is what distinguishes one sugar from another.

The Organic Chemistry of Sugars

Table sugar, sucrose is C12H22O11 and glucose, commonly referred to as blood sugar, is C6H12O6. The subcript numbers denote the number of that atom contained in the sugar molecule.

The definition of carbohydrates also takes us to some additional sugar or saccharide terminology that relates to the complexity of the combined sugars.

Two monosaccharides combine to form disaccharides such as sucrose (table sugar) and multiple monosaccharides combine to form polysaccharides and oligosaccharides.

When three to ten building blocks of simple sugars combine, we have an oligosaccharide. These large sugar molecules have many biological functions of which one critically important one is in cell-to-cell recognition in animals and humans.


Polysaccharides are formed when either monosaccharides or disaccharides join together in repeating chains which can be linear in structure or have numerous branching structures.

They can be huge macromolecules which are characterized by starch or glycogen which are both functionally storage molecules, or cellulose and chitin which functionally act as structural molecules.