Polymers are large molecules that nature relies on

Polymers are large molecules that nature relies on 

Life on Earth is linked to the presence of water, and water is our main constituent. However, all kinds of living species are not simply bags of water but are highly organised. This specialised organisation depends on, among other compounds, macromolecules (Box 1.1), i.e. polymers that are able to retain and structure water, as natural hydrogels. 

Many polymers have a natural origin (mineral, vegetal or animal). Some of these have been used for centuries. In the vegetal kingdom, cellulose is the most abundant macromolecule. Cellulose is a polysaccharide composed of repeating units of cellobiose, i.e. it is a dimer of glucose. 

In the animal kingdom, chitin, a polymer of N-acetylglucosamine, is widely distributed as the main constituent of the shell of arthropods. Proteins and nucleic acids are well known as supports of life, and these natural polymers retain and structure water. 

Macromolecule is a general name for a very large molecule. A high polymer is a macromolecule. A polymer produced by chemical synthesis is usually made from a limited number of repeating units, or monomer units. Polypeptides produced by chemical synthesis are made from amino acids. Proteins that are produced by biosynthesis contain mainly amino acids and may contain a few saccharidic or lipidic units. 

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