Bacterial Cell Structure Quiz

Bacterial Cell Structure

• Cell Appendages: These are structures extending from the bacterial cell.
  • Flagella: Long, thick, and twisted protein structures. Found in Gram-positive and Gram-negative bacteria. May be one, two, or multiple per cell. Used for motility (movement). Examples include Salmonella, Vibrio cholerae, and Escherichia coli.
  • Monotrichous flagellum: Single flagellum.
  • Lophotrichous flagellum: Multiple flagella at one end.
  • Amphitrichous flagellum: Multiple flagella at both ends.
  • Peritrichous flagellum: Multiple flagella all over the cell surface.
  • Axial Filaments (Endoflagella): Found in spirochetes (like Treponema). Run along the bacteria's axis, producing rotational motility.
  • Fimbriae (Pili): Short, thin protein structures. Found in all Gram-negative bacteria and some Gram-positive. Numerous (up to 1000) per cell. Function in adherence to host cells and to each other.
  • Sex Pili: Longer and thicker pili (1-10 per cell). Only in Gram-negative bacteria. Used for gene transfer through conjugation.

Bacterial Cell Envelope

• Capsule: The outermost viscous layer, often found in pathogenic bacteria. Predominantly composed of polysaccharides (e.g., Streptococcus pneumoniae, Neisseria meningitides), but in some cases, polypeptides (e.g., Bacillus anthracis). May act as a virulence factor (making the bacteria more harmful) by preventing phagocytosis. Can be detected by capsule stains (like India ink).

• Cell Wall: Located outside the cytoplasmic membrane. Determines the shape of the cell. Composed of peptidoglycan.

  • Gram-Positive Bacteria: Thick peptidoglycan layer. Contains lipoteichoic acid (for attachment).
  • Gram-Negative Bacteria: Thin peptidoglycan layer in a periplasmic space and an outer membrane. The outer membrane includes lipopolysaccharide (LPS), containing lipid A.

Cytoplasmic Membrane

• Structure: Phospholipid bilayer and proteins
• Functions:
  • Selective permeability and transport of solutes.
  • Energy production (electron transport chain).
  • Excretion of hydrolytic exoenzymes and toxic waste.
  • Biosynthesis of the cell wall.
• Mesosomes: Invaginations of the cytoplasmic membrane into the cytoplasm. Increase the surface area and function in cell division.

Cytoplasmic Contents

• Chromosome: A single circular DNA molecule (double-stranded helix).
• Plasmid: Circular extra DNA segment in some bacteria. Can replicate independently. Often carries genes for antibiotic resistance.
• Ribosomes (70S): rRNA and protein complex. Function in protein synthesis.

Bacterial Spores

• Structure: Resistant structures.

• Formation (Sporulation):

  • Dormant and viable for long periods.
  • Formed by some bacteria (e.g., Bacillus and Clostridium).
  • Process of producing inactive forms from active vegetative cells.
  • DNA enclosed in a multi-layered rigid envelope strengthened by keratin and calcium dipicolinate.

• Spore Germination:

  • In suitable environment, the spore coat is destroyed.
  • Active vegetative cells are produced.
  • Reproduces by binary fission.
  • Examples: spores enter through wounds or via inhalation causing infection/disease.

Antimicrobial Chemotherapy

• Classification:

  • Source: Natural, synthetic, or semi-synthetic.
  • Action: Bactericidal (killing bacteria), or bacteriostatic (preventing growth).
    • Broad spectrum: Effective against many types of bacteria.
    • Narrow spectrum: Effective against a few specific types.

• Target sites for antibiotics:

  • Inhibiting cell wall synthesis. (Beta-lactam antibiotics like Penicillins, Cephalosporins; and Glycopeptides like Vancomycin.)
  • Disrupting cell membranes (Polymyxins).
  • Inhibiting protein synthesis (e.g., Macrolides like erythromycin or Aminoglycosides).
  • Inhibiting nucleic acid synthesis (e.g., Sulfonamides, Quinolones).