Enzyme and metabolism

• Prokaryotes are the most numerous and widespread organisms on earth, and are so classified because they have no defined membrane-bound nucleus
• Prokaryotes


  • Bacteria (or eubacteria)
  • Archaea (or archaebacteria)
• Prokaryotic cell


  • No membrane-bound nucleus
  • Surrounded by a plasma membrane
  • No subcellular organelles, only infoldings of the plasma membrane called mesosomes
  • DNA condensed within the cytosol to form the nucleoid
• Peptidoglycan cell wall


  Protects the prokaryotic cell from mechanical and osmotic pressure
• Some antibiotics, such as penicillin, target enzymes involved in the synthesis of the cell wall
• Gram-positive bacteria


  • Thick cell wall surrounding the plasma membrane
• Gram-negative bacteria


  • Thinner cell wall and an outer membrane, between which is the periplasmic space
• Bacterial flagella


  • Tail-like structures used for movement
  • Rotation of flagella allows bacteria to move through their surrounding media in response to chemicals (chemotaxis)
  • Made of the protein flagellin that forms a long filament attached to the flagellar motor by the flagellar hook
• Bacterial flagella


  • Made of the protein flagellin
  • Rotate rather than bend
• Bacterial flagella movement


  1. Rotation

  2. Allows bacteria to move towards attractants and away from repellents (chemotaxis)
• Flagellar filament

  • Thin helical filament, 15 nm in diameter and 10 µm long
  • Contains 11 subunits in two helical turns
  • Appears as an 11-bladed propeller with a hollow central core