Introduction to the Structure of Prokaryotes

What you’ll learn to do: Describe the structure of prokaryotic cells

There are many differences between prokaryotic and eukaryotic cells. However, all cells have four common structures: the plasma membrane, which functions as a barrier for the cell and separates the cell from its environment; the cytoplasm, a jelly-like substance inside the cell; nucleic acids, the genetic material of the cell; and ribosomes, where protein synthesis takes place. Prokaryotes come in various shapes, but many fall into three categories: cocci (spherical), bacilli (rod-shaped), and spirilli (spiral-shaped) (Figure 1).

Part a: The micrograph shows ball-shaped cocci about 0.9 microns long. Part b: The micrograph shows hotdog-shaped bacilli about 2 microns long. Part c: The micrograph shows corkscrew-shaped spirilli that are quite long and 2 microns in diameter.

Figure 1. Prokaryotes fall into three basic categories based on their shape, visualized here using scanning electron microscopy: (a) cocci, or spherical (a pair is shown); (b) bacilli, or rod-shaped; and (c) spirilli, or spiral-shaped. (credit a: modification of work by Janice Haney Carr, Dr. Richard Facklam, CDC; credit c: modification of work by Dr. David Cox; scale-bar data from Matt Russell)


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