Although each class of polymer is made up of a different type of monomer, the chemical mechanisms by which cells make and break down polymers are basically the same in all cases. In cells, these processes are facilitated by enzymes, specialized macromolecules that speed up chemical reactions. The reaction connecting monomers is a good example of a dehydration reaction, a reaction in which two molecules are covalently bonded to each other with the loss of a water molecule. When a bond forms between two monomers, each monomer contributes part of the water molecule that is released during the reaction: One monomer provides a hydroxyl group (¬OH), while the other provides a hydrogen (¬H). This reaction is repeated as monomers are added to the chain one by one, making a polymer (also called polymerization).
Polymers are disassembled to monomers by hydrolysis, a process that is essentially the reverse of the dehydration reaction. Hydrolysis means water breakage (from the Greek hydro, water, and lysis, break). The bond between monomers is broken by the addition of a water molecule, with a hydrogen from water attaching to one monomer and the hydroxyl group attaching to the other. An example of hydrolysis within our bodies is the process of digestion. The bulk of the organic material in our food is in the form of polymers that are much too large to enter our cells. Within the digestive tract, various enzymes attack the polymers, speeding up hydrolysis. Released monomers are then absorbed into the bloodstream for distribution to all body cells. Those cells can then use dehydration reactions to assemble the monomers into new, different polymers that can perform specific functions required by the cell. (Dehydration reactions and hydrolysis can also be involved in the formation and breakdown of molecules that are not polymers, such as some lipids.)
Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html