While writing your lecture notes, you are trying to develop a way to impart to your students how the removal of a water molecule, a hydroxyl and a hydrogen atom, will be used in making macromolecules. A molecule is a collection of atoms joined through different types of bonds. A macromolecule is the joining of numerous molecules into something that is relatively quite large. The addition of a molecule to a macromolecule, as well as the removal of a molecule from the macromolecule, involves a molecule of water. From past experience you are aware that when you state this to your students many will unfortunately assume you are referring to liquid water. Your students must understand that in biological reactions water, H2O, is actually a hydroxyl group (-OH) and a hydrogen atom (H+) that will be removed or added when altering macromolecules. A dehydration synthesis (removal of water) reforms atomic bonds between molecules to create a larger macromolecule. In a dehydration reaction, a hydroxyl group is removed from one reactant molecule while a hydrogen atom is stripped from another reactant molecule.

Reactant (with hydroxyl group) + Reactant (with hydrogen ion) = Product + H2O

The open bonds will be reformed joining the two molecules, while the hydroxyl and hydrogen atom will be released as water. The reverse of a dehydration synthesis is a hydrolysis reaction, in which a bond between two molecules is stressed by an enzyme and a hydroxyl group when a hydrogen atom is added into the bond. Whereas a dehydration synthesis creates a macromolecule, a hydrolysis reaction breaks one apart.