Practically everything we experience is made up of molecules. These vary in size from simple pairs of atoms, like an oxygen molecule, to complex organic structures. But the biggest molecule in nature resides in your body. It is chromosome 1. A normal human cell has 23 pairs of chromosomes in its nucleus, each a single, very long, molecule of DNA. Chromosome 1 is the biggest, containing around 10bn atoms, to pack in the amount of information that is encoded in the molecule.