Many important polymers are made by living things. They are natural polymers and, like all polymers, they are long chains built from many small repeating units called monomers.
DNA is a polymer. Its monomers are called nucleotides and there are four different ones. Each nucleotide is named after the base it contains: adenine, thymine, guanine and cytosine, often written A, T, G and C. The order of these four nucleotides along the chain is a code that stores genetic information.
Other natural polymers are based on sugars and amino acids. Sugar molecules such as glucose join into long chains to make carbohydrates such as starch and cellulose. Amino acids join into long chains to make proteins. Different proteins have different amino acids in a different order.