Prokaryotic cells are rather simple cells which only consist of a few organelles and lack a true nucleus. In comparison to eukaryotic cells, prokaryotic cells do not have a nucleus which contains their genetic material. Rather, prokaryotic cells contain a nucleoid which is a DNA/protein complex. Additionally, prokaryotic cells have one, double-stranded piece of DNA which is circular.
Figure 1 below provides an image of a prokaryotic cell. If you compare this image with a eukaryotic cell, you will notice that prokaryotes have much fewer organelles. Clearly, prokaryotic cells are much simpler in nature.
Traditionally, prokaryotes were thought of as one group containing archaea and bacteria. However, in the twentieth century it was realized that archaea and bacteria possess a variety of differences and consequently, these organisms have been divided into different groups. Thus, there is a three-domain system representing the forms of life. These three domains are archaea, bacteria and eukaryotes.
Furthermore, although prokaryotes are known as containing simple cells, through time they have diversified. For example, it has recently been discovered that prokaryotes do maintain a cytoskeleton and that some prokaryotes contain membrane bound organelles. Therefore, there is still much to be discovered in the realm of prokaryotes.
1. Wikimedia Commons. (2014). Prokaryote. Retrieved from http://en.wikipedia.org/wiki/Prokaryote
Title Image Credit: Wikimedia Commons