Explain the structure of DNA.

DNA is a polymer made up from monomer units. The monomers that make up a DNA molecule are called nucleotides. Nuceleotides are made up of a nucelic acid (adenine/guanine/thymine/cytosol); a five carbon sugar (deoxyribose); and a phosphate group.

DNA molecules are structured in a double helix. Each DNA molecule is made up from two strands of DNA. The strands are held together by hydrogen bonds between the nucelic acid bases. Adenine and thymine join by two hydrogen bonds, whilst cytosol and guanine join by three hydrogen bonds. This holds the DNA strands together and is called complemetary base pairing. Hydrogen bonds, unlike covalent bonds, can be broken relatively easily which is useful for DNA replication.