Natural polymers

Amino acids have two different functional groups: an amine group (–NH₂) and a carboxylic acid group (–COOH). The simplest is glycine, H₂NCH₂COOH.

Amino acids join by condensation polymerisation. The –NH₂ of one reacts with the –COOH of the next, giving off water at each link. Chains of amino acids are polypeptides, and one or more polypeptides make a protein.

There are about 20 different amino acids. Joining them in different orders gives the huge variety of proteins in living things, including enzymes.

DNA (deoxyribonucleic acid) is a large molecule that carries the genetic instructions for how living organisms and viruses develop and function.

• It is made of two polymer chains (strands).
• The strands are twisted together to form a double helix.
• The monomers are nucleotides. Each nucleotide contains one of four bases: adenine (A), thymine (T), cytosine (C) and guanine (G).
• The bases on the two strands pair up: A with T, and C with G.

The order of the bases is the code for the genes.

Plants make two important natural polymers from sugar (glucose) monomers:

• Starch — an energy store in plants, found in foods such as potatoes and rice.
• Cellulose — gives strength to plant cell walls.

So the main natural polymers are proteins (from amino acids), DNA (from nucleotides), and starch and cellulose (from sugars).