Prokaryotes are single-celled organisms that lack a nuclear envelope. Their DNA is not enclosed within a membrane-bound nucleus, but is instead located in an area of the cell called the nucleoid. Prokaryotes are further divided into two groups: bacteria and archaea.
Bacteria are the best-known type of prokaryote. They are very diverse, ranging in size from 0.2 to 20 micrometers (µm). Most bacteria have a cell wall that gives them their shape and helps protect them from their environment. Some also have a capsule, an extra layer outside the cell wall.
Archaea are less well known than bacteria, but they are just as important. They were first discovered in 1977, when scientists were looking for life in extreme environments (such as hot springs or deep sea vents). Archaea are also found in more “ordinary” habitats, such as soil and the gut of animals.
Like bacteria, archaea come in many different shapes and sizes. However, they do not have a cell wall; instead, their cell membrane is surrounded by a shell made of proteins.
Both bacteria and archaea are classified as prokaryotes because they lack a nuclear envelope around their DNA—in other words, their DNA is not contained within a membrane (as it is in eukaryotic cells). Although prokaryotes are simple compared to eukaryotes (organisms with cells that contain a nucleus), they play vital roles in nearly all ecosystems on Earth
Prokaryotes
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