Monomers: Types & Examples

What are Monomers?

A monomer is a small molecular subunit that can be combined with similar subunits to form larger molecules. In living systems, like our own bodies, these larger molecules include carbohydrates, lipids, nucleic acids and proteins.

The monomers of these organic groups are:

• Carbohydrates – monosaccharides
• Lipids – glycerol and fatty acids
• Nucleic acids – nucleotides
• Proteins – amino acids

Monosaccharides

A monosaccharide is the monomer of a carbohydrate. Carbohydrates, such as sugars and starches, store energy. Others, such as cellulose and chitin, are structural in nature.

Some monosaccharides are isomers .This means that they have the same chemical formula but a different arrangement of atoms. An example of such a pair of isomers is glucose and fructose. They both have the formula C6 H12 O6, but glucose has a ring with five carbons and one oxygen, while fructose has a ring with four carbons and one oxygen.

Glucose is a common source of energy for living things. It is easily broken down by most cells in a process called glycolysis. Many cells break it down further during aerobic respiration. Glucose monomers can be put together to make starch and glycogen. Plants store energy as starch, while animals store it as glycogen. Structural carbohydrates, such as cellulose in plant cell walls and chitin in the exoskeleton of insects, are also made of glucose monomers.

Fructose, which we already learned is an isomer of glucose, is a simple sugar that gives fruits and vegetables their sweet taste. Sometimes, a single glucose and a single fructose will combine to form sucrose, or common table sugar, which is a disaccharide, or a sugar composed of two monosaccharides.

Glycerol and Fatty Acids

Glycerol and fatty acids are the monomers of lipids. Lipids include waxes, oils and fats. Some are used for energy storage. Others cushion bony parts of the body. Waxes can protect a plant or animal surface from dehydration. Lipids are also an important component of the cell membrane.

Glycerol is a sweet-tasting molecule with applications in the food and pharmaceutical industries. It’s also the backbone of triglycerides, which are a type of fat found in our blood.

There are three main types of fatty acids – saturated, monounsaturated and polyunsaturated – based on the number of hydrogen atoms present. Let’s take a brief look at how fatty acids are composed. A fatty acid is made of a carboxyl group with a chain of carbons attached. When the carbon chain has no double or triple bonds, it is said to be saturated. This means that each carbon has bonded with two hydrogen atoms, except for the last one, which has bonded with three. In an unsaturated fat, there are one or more fatty acids that have one or more double or triple bonds. These bonds form between consecutive carbons.