AQA GCSE Chemistry

Revision Notes

7.3.4 DNA & Natural Polymers


  • Deoxyribonucleic acid (DNA) is a large molecule which is essential to all life
  • It contains genetic information which it encodes as instructions which organisms need to develop and function correctly
  • DNA consists of four different monomers called nucleotides which contain small molecules called bases and which are abbreviated to A, T, C, and G which are bound together by polymerisation
  • The nucleotides form two strands that intertwine, giving the famous double helix shape of DNA
  • The bases on either polymer chain pair up in specific sequences forming cross links that hold the strands together, giving rise to the double helix shape
  • It is a complex molecule that contains genetic information which is stored in the order in which the bases organise themselves, which is a code for the organisms gene

The DNA helix is made from two strands of DNA held together by hydrogen bonds, IGCSE & GCSE Biology revision notes

Diagram showing the complex double helix structure of DNA

Natural Polymers

Starch & Cellulose

  • Carbohydrates are compounds of carbon, hydrogen and oxygen with the general formula Cx(H2O)y
  • There are simple carbohydrates and complex carbohydrates
  • Simple carbohydrates are called monosaccharides and are sugars such as fructose and glucose
  • Complex carbohydrates are called polysaccharides such as starch and cellulose
  • The monomers from which starch and cellulose are made are both sugars
  • Starch is used to store energy and cellulose is a stiff polymer used in plant cell walls to provide support
  • Complex carbohydrates are condensation polymers formed from simple sugar monomers and, unlike proteins, are usually made up of the same monomers
  • An H2O molecule is eliminated when simple sugars polymerise
    • The linkage formed is an -O- linkage and is called a glycosidic linkage

Amylose, IGCSE & GCSE Chemistry revision notes

Diagram of the starch amylose showing glycosidic linkages (-O-) which bind the monomers together, Amylose makes up approximately 20-30% of starch

Other Natural Polymers

  • Proteins are also important natural polymers with specific biological functions
  • Some examples of proteins and their functions include:
    • Haemoglobin which transports oxygen in the blood
    • Antibodies in the immune system help protect the body from viruses and bacteria
    • Enzymes which are biological catalysts

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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