Prokaryotic Cells

Cells are broadly categorised based on the presence of the nucleus as either prokaryotes or eukaryotes. The organisms that are single-celled or unicellular with no organised nuclear membrane-bound nucleus or organelle are called prokaryotic cells. The word ‘prokaryote’ in Greek means ‘before nucleus’. The prokaryotic cells are not only the most ancient form of life on earth but also the tiniest organisms to survive independently.

Prokaryotes, which comprises all the different types of bacteria is sub-divided into two main groups – Archaebacteria and Eubacteria. Archaebacteria (archaea) are the organism that can inhabit extreme environments on the earth, varying from the high-temperature regions like hydrothermal vents or hot springs to the regions with extreme high pH water. Eubacteria also called as the ‘true bacteria’ are far more common in our daily life in comparison to archaebacteria.

The common parts of prokaryotic cells are a plasma membrane to separate the cell from the external environment, a semi-fluid like substance called cytosol where organelles are found, DNA the genetic material and ribosome for protein synthesis.

Characteristics of Prokaryotic Cells

  1. Prokaryotic cells do not possess any membrane-bound organelles like the Golgi apparatus, endoplasmic reticulum, vacuoles, lysosomes and mitochondria.
  2. The prokaryotic cells vary in size from 1-2 micrometre in diameter to few micrometres in length.
  3. The DNA in the prokaryotic cell is present in a non-membrane bound region located in the cytoplasm of the cell called nucleoid.
  4. The prokaryotic cell reproduces asexually by a simple biological process called binary fission.
  5. The prokaryotic cells have a larger surface-area-to-volume ratio allowing higher nutrient flow rate and thus faster growth rate.

Example of Prokaryotic Cells

All Bacteria and archaea are counted as prokaryotes. Some of the examples of prokaryotic cells are Bacillus subtilis, Escherichia coli, Pseudomonas.


References:

Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. The Origin and Evolution of Cells. Available from: https://www.ncbi.nlm.nih.gov/books/NBK9841/

Domain Bacteria, Biodiversity, The Ohio State University at Lima  ↵

Fuerst , J. A. (2010) Beyond Prokaryotes and Eukaryotes : Planctomycetes and Cell Organization. Nature Education 3(9):44


External links:

Lumen Learning – Prokaryotic Cells

HyperPhysics – Prokaryotic Cells


Last Updated: Jan 9, 2019


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