Intro to Prokaryotes and Viruses
Prokaryotes are microscopic organisms that include the domains Bacteria and Archaea. Prokaryotes lack a nucleus, and they have no organelles except ribosomes. The hereditary material exists as a single loop of double-stranded DNA in a nuclear region, or nucleoid. Prokaryotic cells multiply by an asexual process called binary fission. No evidence of mitosis is apparent in the reproductive process.
Prokaryotic cells live in virtually all environments on Earth, including soil, water, and air. They have existed for approximately 3.5 billion years, and they have evolved into every conceivable ecological niche on, above, and below Earth’s surface.
Prokaryotic cells are often categorized according to their shapes. The spherical bacteria are referred to as cocci (the singular is coccus); the rod-shaped bacteria are bacilli (the singular is bacillus); and the spiral bacteria are spirochetes if they are rigid or spirilla (the singular is spirillum) if they are flexible.
Recent research has focused on the microbiome and the important role prokaryotes play in human health and disease. The microbiome is the numerous bacterial communities found on and within the human body. Our intestines alone are home to approximately 700 species of prokaryotes, and their numbers outnumber all human cells in the body tenfold.