2.2.3—Role of covalent bonds in forming polymers

A polymer is made when many monomer subunits are joined by strong covalent bonds. These bonds provide a stable backbone, while the repeating subunits give the polymer its overall structure and possible biological role.

• Join: complementary reactive groups on subunits form a covalent link, creating a larger molecule from smaller units.
• Condensation: when the link forms, a water molecule is removed; repeating this process builds a polymer.
• Representative links: glycosidic bonds join monosaccharides in carbohydrate polymers, while ester bonds join glycerol to fatty acids in lipids such as triglycerides.
• Break: hydrolysis uses water to break a covalent link, allowing a polymer or larger molecule to become smaller subunits again.

The bond type follows the subunits being joined, so “covalent bond” is the broad idea and glycosidic or ester bond names identify particular biological links. Cells can assemble stable storage or structural molecules by condensation and later digest or mobilise them by hydrolysis.

Do not describe a polymer as a loose association held only by weak attractions, and do not reverse the processes: condensation forms the link and removes water; hydrolysis breaks the link and adds water. A large molecule is not automatically a polymer unless it is built from repeating subunits.