Prokaryotic cell components

Usually prokaryotes are unicellular (but not always). Although microbes are commonly unicellular, these grow in colony and some types of bacteria can form biofilm that enhances their survival.

Note: word “cyto” – refers to “cell”, a word originated from Greek. (Dictionarycom.)

Here are the basic cell components of prokaryotes:


All cells have: (also found in Eukaryotes)

  • Cell Wall (not found in animal cell)
    • This is rigid strong outer layer that protects cell from osmosis (bursting) and supports the cell by maintaining the shape.
    • In prokaryotes, it is often made out of peptidoglycan
    • In eukaryotes, (fungi, plants) it is often made out of cellulose
  • Cytoplasmic membrane/plasma membrane/cell membrane
    • This is a barrier that separates the inside of the cell from the outside of the cell.
    • Function is to control what nutrients can enter/exit the cell. This can serve to protect cell from harmful substances like antibiotics.
  • Cytoplasm
    • This is aqueous mixture containing macromolecules, ions, proteins, ribosomes etc. that fills the dead space inside the cell.
    • Molecules found in cytoplasm are essential for efficient metabolism.
  • Ribosomes
    • These are found within cytoplasm, and is the site of protein synthesis.

Components only specific to prokaryotes

  • Nucleoid region
    • Randomly/irregular shaped region in cytosol/cytoplasm of prokaryotic cell housing DNA. There is no membrane. It is an open region where various enzymes, RNA and proteins are found for cellular metabolism.
    • Note that no nucleus membrane is what allows mRNA and protein synthesis to occur at the same time for some prokaryotes.
  • Plasmid
    • This is a piece of DNA that carries non-essential (often) or sometimes essential genes. For example, it could be genes for antibiotic resistance.
  • Flagellum (exception, found in protozoan (euk.)
    • This is long microtubule structure that allows cell to move
  • Pili
    • Proteinaceous and multi-subunit structure. (kline et al., 2010)
    • These are used to attach to surfaces/epithelial cells/other cells (biofilm), an important virulence factor for an infection in many microbes. (Schilling et al., 2001)
  • Outer membrane (only found in Gram negative bacteria) (Brown et al., 2015)
    • It contains lipopolysaccharides (LPS) and various porins/efflux pump, transporters which confer bacteria with antibiotic resistance.
    • LPS is large polymer that have three parts: lipid A, core oligosaccharide and O-antigen. (Gu et al., 2015)
    • Detailed structure drawing: Peptidoglycan structure and function
  • Periplasmic space (in Gram negative bacteria)
    • This is a region between cell membrane and outer membrane of cell
    • There are various enzymes for hydrolysis, chemoreceptors and binding proteins. This space is also where transportation, degradation and motility is carried out.


Brown, L., Wolf, J. M., Prados-Rosales, R. and Casadevall, A. Nat. Rev. Microbiol. (2015) 13: p. 620-630.

Cell Functions. Cell Functions. ( (accessed Feb. 2, 2017).

cyto-. Dictionarycom. ( (accessed Feb. 2, 2017).

Gu, Y., Stansfeld, P. J., Zeng, Y., Dong, H., Wang, W. and Dong, C. Structure. (2015) 23 (3): p. 496-504.

Kline, K. A., Dodson, K. W., Caparon, M. G. and Hultgren, S. J. Trends. Microbiol. (2010) 18(5): p. 224-232.

-24 The periplasm is between the cytoplasmic and outer membranes in gram-negative bacteria. Through the Microscope Main News RSS. ( (accessed Feb 2, 2017″.

Schilling, J. D., Mulvey, M. A. and Hultgren, S. J. Jou. Infect. Dis. (2001) 183 (Supplement 1): p. 36-40.


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