The unit of heredity, the gene, is made up of nucleic acids. In humans, genes are made up of DNA. The other nucleic acid is the RNA. The chemical structure of a DNA molecule allows it to be configured as a two-stranded molecule. The RNA molecules work as functional intermediaries that help in the physical expression of genes in the form of complex proteins. The entire complement of DNA molecules in the nucleus of a cell undergoes replication before cell division. RNA inhabits the cytoplasm of a cell.