1.3 Introduction to Biological Macromolecules

The four macromolecules

Life is built from four classes of large molecules: carbohydrates, lipids, proteins, and nucleic acids. Three of them — carbohydrates, proteins, and nucleic acids — are polymers: long chains of repeating subunits called monomers. Lipids are the exception; they are not true polymers of a single repeating monomer.

Building up: dehydration synthesis

Monomers link together through dehydration synthesis (also called condensation): a hydroxyl (–OH) and a hydrogen are removed as a molecule of water, and a new covalent bond forms between the monomers. Building a polymer therefore *releases* water.

Breaking down: hydrolysis

The reverse reaction is hydrolysis — 'water-splitting.' Adding a water molecule breaks the bond between two monomers. This is how your body digests food: large polymers are hydrolyzed back into monomers. Monomers by class: carbohydrates → monosaccharides, proteins → amino acids, nucleic acids → nucleotides.

Key terms

Monomer

A small repeating subunit that links together to build a polymer.

Polymer

A large molecule made of many monomers bonded together.

Dehydration synthesis

Joining monomers by removing a water molecule; forms a covalent bond.

Hydrolysis

Breaking a polymer apart by adding a water molecule.

The four macromolecules

Carbohydrates, lipids, proteins, and nucleic acids.

Try an AP-style question

Joining 10 glucose monomers into a linear polysaccharide releases how many water molecules?

1. 10
2. 11
3. 9
4. 20