All living things are made up of four classes of large biological molecules: Carbohydrates Lipids Proteins nucleic acids Macromolecules are large molecules composed of thousands of covalently connected atoms Molecular structure and function are inseparable A polymer is a long molecule consisting of many similar building blocks These small building-block molecules are called monomers Three of the four classes of life?s organic molecules are polymers: Carbohydrates Proteins Nucleic acids A condensation reaction or more specifically a dehydration reaction occurs when two monomers bond together through the loss of a water molecule Enzymes are macromolecules that speed up the dehydration process