Proteins (Cambridge International IGCSE Chemistry)

Spec point — 11.3.4 · Describe proteins as natural polyamides and that they are formed from amino acid monomers with the general structure: where R represents different types of side chain Describe and draw the structure of proteins as: (see IMAGE in syllabus)

Proteins

Extended tier only

• Proteins are an example of condensation polymers
• They are formed from amino acid monomers joined together by amide links
• Amino acids are small molecules containing NH₂ and COOH functional groups
• Due to containing amide links and being found in biological systems, proteins are known as natural polyamides
• In proteins, the amide links are known as peptide links
• There are twenty common amino acids, each differing by their side chain, represented by R

General structure of an amino acid

• Proteins can contain between 60 and 600 of these amino acids in different orders
• These are the monomers which polymerise to form the protein

The formation of a protein

A protein is produced by a condensation polymerisation reaction

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

Diagram showing a section of protein

Exam Hint For your exam, you are only required to draw proteins using the boxes representing the carbon chains.