DNA is a polymer made from nucleotide monomers. Describe the structure of DNA, including the type of polymerisation used to form it and the number of different monomers involved.

DNA is a polymer of nucleotides.
1. Each nucleotide consists of a phosphate group, a five‑carbon sugar (deoxyribose) and a nitrogenous base.
2. There are four different nucleotides: adenine, thymine, cytosine and guanine.
3. DNA is formed by condensation (dehydration) polymerisation, where a water molecule is released when a phosphate group links to the 3′‑hydroxyl of one sugar and the 5′‑phosphate of the next.
4. The result is a chain of phosphodiester bonds.
5. Most DNA molecules are double‑stranded, with two polymer chains wound into a right‑handed double helix, the strands running antiparallel and base‑paired by hydrogen bonds.