Prokaryotes Objectives: Know the Differences between Viruses and Bacteria How do viruses and bacteria cause disease? What is a prokaryote? Prokaryotes are defined as unicellular organisms that lack a nucleus. Unicellular means: that these are single celled organisms. lack a nucleus means that prokaryotes have genetic material (DNA) but it is not separated from the rest of the cell by a membrane. Two Types of Prokaryotes Bacteria : 1) Larger Domain (more species) 2) Live almost everywhere 3) Have a cell wall made of peptidoglycan