A hydrolysis reaction uses water to break a covalent bond in a larger molecule, producing smaller molecules. In IB Biology, hydrolysis commonly breaks biological polymers into their monomers and is the reverse of a condensation reaction.
How Hydrolysis Works
The word “hydrolysis” means splitting using water. A water molecule is divided into an group and an group, which are added to the two products formed when the covalent bond breaks.
For a generalized dimer:
Hydrolysis reactions are usually catalysed by enzymes because uncatalysed reactions may occur too slowly to support life. During digestion, for example, enzymes hydrolyse large, insoluble food molecules into smaller molecules that can be absorbed.
| Biological molecule | Example of hydrolysis |
|---|---|
| Carbohydrate | Maltose and water are hydrolysed to form two glucose molecules. |
| Protein | Peptide bonds are hydrolysed, producing amino acids. |
| Triglyceride | Ester bonds are hydrolysed, producing glycerol and three fatty acids. |
Hydrolysis Versus Condensation
| Hydrolysis | Condensation |
|---|---|
| Uses a water molecule | Produces a water molecule |
| Breaks a covalent bond | Forms a covalent bond |
| Usually produces smaller molecules | Usually produces a larger molecule |
| Involved in digestion and breakdown | Involved in building macromolecules |
A common misconception is that water merely provides the environment for hydrolysis. In fact, water is a reactant: its components become incorporated into the products.
IB Exam Technique
This is assessed at both SL and HL in subtopic B1.1, Carbohydrates and lipids. For an explain question, state that water is split, identify that a covalent bond is broken, and show that and are added to the products. Do not simply write that hydrolysis “breaks molecules down”; specify the role of water and name the bond or products when the question provides a particular molecule.
