A chromosome is packaged and organized chromatin, a complex of macromolecules found in cells, consisting of DNA, protein and RNA. The main information-carrying macromolecule is a single piece of coiled double-stranded DNA, containing many genes, regulatory elements and other non-coding DNA. The DNA-bound macromolecules are proteins, which serve to package the DNA and control its functions. Chromosomes vary widely between different organisms. Some species also contain plasmids or other extrachromosomal DNA.