DNA is found in all prokaryotic and eukaryotic cells, as well as in a number of viruses. The molecule carries the chemical information that is essential for the direction of protein synthesis and cell replication. In human cells, DNA is wrapped around a complex of histone proteins, forming what is known as chromatin. Chromatin undergoes a process of condensation for cell division or the production of gametes, developing into the higher-order structures called chromosomes. Only one human DNA molecule is present per chromosome. However, many lower types of organisms, such as viruses and bacteria, do not form organized chromosomes at all, though they may still contain DNA.