Hydrolysis
Polymers are broken down into monomers in a process known as hydrolysis, which means to split water. Basically, hydrolysis is a reaction in which a water molecule is used during the breakdown (see image below). During these reactions, the polymer is broken into two components. One part gains a hydrogen atom (H+) and the other gains a hydroxyl molecule (OH–) from a split water molecule.
In the hydrolysis reaction shown here, the disaccharide maltose is broken down to form two glucose monomers with the addition of a water molecule. Note that this reaction is the reverse of the synthesis reaction above. Image Attribution: OpenStax Biology
Dehydration and hydrolysis reactions are catalyzed, or “sped up,” by specific enzymes. Dehydration reactions involve the formation of new bonds, requiring energy, while hydrolysis reactions break bonds and release energy. These reactions are similar for most macromolecules. However, each monomer and polymer reaction is specific for its class.
For example, in our bodies, food is hydrolyzed, or broken down, into smaller molecules by catalytic enzymes in the digestive system. In fact, this allows for easy absorption of nutrients by cells in the intestine. Each macromolecule is broken down by a specific enzyme. For instance, carbohydrates are broken down by amylase, sucrase, lactase, or maltase. Human saliva is rich in amylase.
This image shows a laboratory experiment involving the hydrolysis of starch derivatives. Image Attribution: “Hydrolysis,” by Commonwealth Scientific and Industrial Research Organisation (CSIRO) via Wikimedia Commons (CC BY 3.0)
Similarly, proteins are broken down by the enzymes pepsin and peptidase, and by hydrochloric acid. Lipids are broken down by lipases. As a matter of fact, breakdown of these macromolecules provides energy for cellular activities.
Video Summarizing Hydrolysis and Dehydration Synthesis
The video below by Ricochet Science is a quick and easy overview of hydrolysis and dehydration synthesis.