Cell Biology

• Cell wall


  Present beneath the slime layer or capsule
• Cell wall


  • Gives characteristic shape to the bacteria
  • Gives protection against mechanical and chemical injury
• Cell wall of all eubacteria

  Contains a material murein or peptidoglycan
• Murein or peptidoglycan


  Consists of polysaccharide chains cross linked with short amino acid chains
• Bacteria


  Could be gram positive or gram negative based on cell wall structure
• Cell surface membrane


  • A thin membrane lying beneath the cell wall, differentially permeable like in eukaryotic cells
  • May be folded inward in some cells to form mesosomes and photosynthetic membranes
  • Enzymes associated with respiration are found on the surface of mesosomes
• Cytoplasm


  • Appears granular due to the presence of ribosomes
  • Contains stored food, lipid, glycogen granules, and other materials dispersed through it
• Genetic material


  • In the form of single circular DNA attached to the surface membrane (internally) at a point
  • Bacteria lack a nuclear membrane
  • The space in the cytoplasm that is held by the DNA (genetic material) is called nucleoid
• Flagella


  • Many bacteria are equipped with one or more flagella
  • Helps bacteria move and respond to certain stimuli
  • Simple in structure and resemble just one of the microtubules of eukaryotic flagella
  • Originates from a basal structure in the cell membrane
• Pilli or fimbriae


  • Shorter and thinner than flagella
  • Project from the walls of some gram negative bacteria
  • Help in the attachment of these strains with other cells or surface