Prokaryotic Cells


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•  Prokaryotes have a simple cell structure without compartmentalisation

Prokaryotes are organisms whose cells lack a nucleus  ('pro' = before ; 'karyon' = nucleus)

They belong to the kingdom Monera and have been further classified into two distinct domains:

  • Archaebacteria – found in extreme environments like high temperatures, salt concentrations or pH (i.e. extremophiles)
  • Eubacteria – traditional bacteria including most known pathogenic forms (e.g. E. coli, S. aureus, etc.)

Prokaryotic Features

Prokaryotic cells will typically contain the following cellular components:

  • Cytoplasm – internal fluid component of the cell
  • Nucleoid – region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)
  • Plasmids – autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer) 
  • Ribosomes – complexes of RNA and protein that are responsible for polypeptide synthesis (prokaryote ribosome = 70S)
  • Cell membrane – Semi-permeable and selective barrier surrounding the cell
  • Cell wall – rigid outer covering made of peptidoglycan; maintains shape and prevents bursting (lysis)
  • Slime capsule – a thick polysaccharide layer used for protection against dessication (drying out) and phagocytosis
  • Flagella – Long, slender projections containing a motor protein that enables movement (singular: flagellum)
  • Pili – Hair-like extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)

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•  Prokaryotes divide by binary fission

Binary fission is a form of asexual reproduction used by prokaryotic cells

In the process of binary fission:

  • The circular DNA is copied in response to a replication signal
  • The two DNA loops attach to the membrane
  • The membrane elongates and pinches off (cytokinesis), forming two cells

Overview of Binary Fission and Rate of Bacterial Growth

binary fission