DNA is a polymer that forms a double helix structure. Describe the structure of DNA and explain how it is replicated inside a cell.

DNA is a polymer of nucleotides, each consisting of a phosphate, a deoxyribose sugar and a nitrogenous base. Two strands of nucleotides are twisted around each other to form a right‑handed double helix. The bases are adenine, thymine, cytosine and guanine and they pair by complementary base‑pairing – A with T and C with G – which holds the two strands together.

During replication, which takes place in the nucleus, the double helix is unwound by helicase. The two strands separate and each acts as a template. DNA polymerase then adds complementary nucleotides to each template strand, forming two new strands. Because each original strand is copied, two identical DNA molecules are produced.