Natural Polymers (Edexcel GCSE Chemistry)

Natural Polymers

DNA

• 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

Diagram showing the complex double helix structure of DNA

Starch

• Carbohydrates are compounds of carbon, hydrogen and oxygen with the general formula C_x(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

• The monomers from which starch is made are sugars

• Starch is used to store energy

• 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

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

Proteins

• Proteins are condensation polymers which are formed from amino acid monomers joined together by peptide bonds

• Amino acids are small molecules containing amine (-NH₂) and carboxylic acid (-COOH) functional groups

The structure of naturally occurring amino acids have an amino group on the second carbon along from the carboxyl group. The R represents a varying side group.

• A peptide link is formed when a carboxylic acid and an amine react:

Amino acids join together to form dipeptides and long chains of amino acids which are the polymers that make up proteins

• Proteins are 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