There are two types of carbohydrates:
The simple sugars
Glucose, sucrose, fructose (and many others)
The complex carbohydrates.
Carbohydrates that are made of long chains of sugars
All carbohydrates are made up of units of sugar (also called saccharide units).
Carbohydrates that contain only one sugar unit are called monosaccharides.
Disaccharides have two sugar units bonded together.
For example, common table sugar is sucrose (below), a disaccharide that consists of a glucose unit bonded to a fructose unit.
Complex carbohydrates are polymers of the simple sugars.
In other words, the complex carbohydrates are long chains of simple sugar units bonded together.
For this reason the complex carbohydrates are often referred to as polysaccharides.
Starch (below) is a polymer of the monosaccharide glucose (n is the number of repeating glucose units and ranges in the 1,000's).
Starches and cellulose are complex carbohydrates used by plants for energy storage and structural integrity.
Glycogen, another polymer of glucose, is the polysaccharide used by animals to store energy.
Both starch and glycogen are polymers of glucose.
Starch is a long, straight chain of glucose units, whereas glycogen is a branched chain of glucose units.
Proteins are polymers of amino acids.
Amino acids all have the general structure:
The R in the diagram represents a functional group that varies depending on the specific amino acid in question.
Twenty amino acids in human metabolism
When 2 amino acids bond together, water is released as the carboxyl end of one amino acid bonds to the amine end of the adjacent one forming a peptide bond, as illustrated at the left.