O LevelChemistryCambridge (CIE)Revision Notes11. Organic Chemistry11.8 PolymersProteins

Proteins (Cambridge (CIE) O Level Chemistry): Revision Note

Exam code: 5070

Written by: Caroline Carroll

Reviewed by: Lucy Kirkham

Updated on 19 October 2026

Proteins

Proteins are condensation polymers which are formed from amino acid monomers joined together by amide links (in proteins also known as a peptide link) similar to the structure in nylon
The units in proteins are different however, consisting of amino acids
An amino acid has an -NH₂ group and a -COOH group attached to the same carbon, along with a hydrogen atom and a side chain, R

General structure of an amino acid

There are twenty common amino acids, each differing by their side chain, represented by R
Proteins can contain many of these amino acids, joined in different orders
These are the monomers which polymerise to form the protein

Formation of a peptide link by condensation. Two amino acids are drawn as displayed formulae side by side; a hydrogen atom on the amine group of one and the hydroxyl group on the carboxyl group of the other are picked out in red inside a box. An arrow labelled condensation leads to the product, in which the nitrogen and the carbon are now joined directly. That new link is boxed and labelled peptide link, and a molecule of water is shown as the other product.

Diagram showing condensation polymerisation to produce a protein

The structure of proteins can be represented using the following diagram whereby the boxes represent the carbon chains

A section of a protein chain drawn as a displayed formula. The chain repeats a nitrogen atom carrying a hydrogen, then a shaded block standing for an amino acid side chain, then a carbon atom double bonded to an oxygen. Three blocks are shaded differently to show that the side chains vary along the chain.

Diagram showing a section of protein

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Author: Caroline Carroll

Expertise: Head of Content Delivery

Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about delivering high-quality resources to help students achieve their full potential.

Reviewer: Lucy Kirkham

Expertise: Content Creator

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.