Monomers & Polymers

01Monomers & Polymers

Monomers and polymers

This section covers monomers, polymers and the relationship between small biological units and the larger molecules they form.

Small units and larger molecules

A monomer is a small molecular unit that can act as a building block for a larger biological molecule. Important examples are monosaccharides, amino acids and nucleotides.

A polymer contains a large number of monomer units linked together. Joining many monomers in this way produces a much larger molecule.

Although organisms are extremely diverse, the underlying molecular basis of life is shared: the same principal types of biological building unit occur throughout living organisms.

Monomer	Example of a larger molecule built from these units
Monosaccharides	Polysaccharides
Amino acids	Polypeptides
Nucleotides	Nucleic acids

Monomer

A small unit from which a larger biological molecule can be constructed.

Polymer

A larger molecule containing many linked monomer units.

Exam Tip: If asked about monomers and polymers, support the definitions with an appropriate example, such as nucleotides being the monomer units found in nucleic acids.

02Monomers & Polymers

Condensation reactions

This section covers how condensation joins two molecules by forming a chemical bond while water is eliminated.

Forming a bond

During a condensation reaction, two molecules become joined by a new chemical bond. At the same time, a molecule of water is eliminated.

Repeated condensation reactions allow many monomer units to become linked into larger molecules.

Two molecules are joined.
A new covalent chemical bond forms between them.
An OH and an H are removed from the reacting molecules.
These contribute to the molecule of water that is eliminated.

\text{two molecules}\longrightarrow\text{joined molecule}+\ce{H2O}

Building larger molecules

Condensation is therefore an important way of constructing larger biological molecules from smaller units. Each reaction creates a bond between the participating molecules and removes water.

Worked example: A monomer is added to the end of a growing molecule.

A chemical bond forms between the incoming monomer and the existing molecule. An H and an OH are removed during the reaction and water is produced. Repeating this process allows additional monomer units to be joined.

Exam Tip: A complete description of condensation should identify both linked events: formation of a chemical bond and elimination of water.

03Monomers & Polymers

Hydrolysis reactions

This section covers how hydrolysis uses water while breaking a chemical bond between joined molecules.

Breaking a bond

In a hydrolysis reaction, a molecule of water is used as a chemical bond is broken. The molecules that had been joined are consequently separated.

Hydrolysis has the opposite overall effect to condensation. Condensation builds a bond while eliminating water; hydrolysis uses water while breaking a bond.

A molecule of water is used.
The covalent bond between two joined units is broken.
The components of water contribute H and OH to the separated molecules.
Repeated hydrolysis can break a larger polymer into progressively smaller molecules and ultimately its monomer units.

\text{joined molecule}+\ce{H2O}\longrightarrow\text{two separated molecules}

Condensation and hydrolysis compared

Feature	Condensation	Hydrolysis
Overall effect	Joins molecules	Separates joined molecules
Chemical bond	Formed	Broken
Water	Eliminated	Used

Exam Tip: When describing hydrolysis, state explicitly that water is used and a chemical bond is broken. Saying only that the molecule splits does not identify the chemical changes.