Cell shape and Size

• Distinguishing characteristics of prokaryotic cells

  • DNA not enclosed within a membrane
  • Lack other membrane-bound organelles
  • DNA not associated with histone proteins
  • Cell walls almost always contain the complex polysaccharide peptidoglycan
  • Reproduction usually by binary fission
• Vibrios

  • Vibrio parahaemolyticus
  • Spirillum volutans
• Square bacterium


  • Haloquadratum walsbyi
• star-shaped

  • Stella vacuolata and Stella humosa
• Advantages of small size

  • Higher surface-to-volume ratio
  • Higher growth rate
  • Higher mutation rate
• Thiomargarita namibiensis


  • Size: 750 µm, Cell volume: 200,000,000 µm3
• Escherichia coli


  • Size: 1 x 2 µm, Cell volume: 2 µm3
• Bacteria are prokaryotic, single-celled organisms that can be found everywhere on Earth.
• Viruses are not considered living organisms because they cannot reproduce or carry out metabolic processes without the presence of host cells.
• Archaea is another type of microbe that was once classified as bacteria but has since been reclassified due to differences in their genetic makeup.
• Fungi are eukaryotes with cell walls made up of chitin instead of cellulose like plants.
• coccus


  ety. grain or seed. it is any spherical or roughly spherical bacterium.
• rod/bacillus/cigar-shaped


  also called bacilliform bacterium
• Spirillum


  ety. a coil. cork screw shape to a gently curved shape.
• vibrios


  ety. to wave. a curved-rod shape similar to a comma.
• Spirochete


  ety. in spiral + long hair. slender and spiral in shape. its movement is through spinning and flexing about the long axis. they are more flexible than spirillum.
• pleiomorphic 


  Mycoplasma pneumoniae
• square

  Haloquadratum walsbyi
• diplococci

  one plane of division. do not detach from each other when dividing.
• streptococci


  one plane of division with chain-like arrangement. do not detach from each other when dividing.
• tetrad

  two planes of division. aerococcus, pedicoccus, tetragenococcus
• sarcinae


  three planes of division. sarcina ventriculi, sarcina ureae.
• staphylococci

  grape-like shaped that are randomly stacked
• Palisades


  chinese characters/chinese letters arrangement. clusters of cells attached to one end of the previous cells.