Microbiology Basics: Prokaryotes vs Eukaryotes

Microbiology

• Microbiology is the science of microorganisms (small living organisms).
• Microorganisms include bacteria, viruses, and fungi.
• These organisms are too small to be seen with the naked eye and require a microscope.

Prokaryotes and Eukaryotes

• Prokaryotes:
  • Primitive or premature cells.
  • Lack a true nucleus and membrane-bound organelles.
  • Their genetic material (DNA) is not enclosed in a membrane.
  • Examples include bacteria and rickettsia.
• Eukaryotes:
  • True cells
  • Contain a true nucleus, which is a membrane-bound compartment holding the cell's DNA.
  • Have membrane-bound organelles.
  • Examples include fungi.

Bacterial Cell Structure

• Essential Structures (found in all bacteria):
  • Cell wall
  • Cytoplasmic membrane
  • Cytoplasm
  • Nuclear body (nucleoid)
• Additional Structures (some, but not all bacteria have these):
  • Capsule
  • Flagella
  • Fimbriae (pili)
  • Inclusion granules

Bacterial Cell Wall

• Forms the outer rigid layer of the cell.
• Composed of peptidoglycan (carbohydrate and protein).
• Responsible for the rigidity of the cell wall.
  • Gram-positive bacteria have a thicker peptidoglycan layer (80%).
  • Gram-negative bacteria have a thinner peptidoglycan layer (20%).
• Gram-positive bacteria have teichoic acid in their cell walls.
• Gram-negative bacteria have lipopolysaccharides (LPS) in their cell walls, which are made of a lipid A, core polysaccharide, and O-antigen regions.
• The periplasmic space is the area between the cell wall and the cytoplasmic membrane containing peptidoglycans and enzymes.

Cytoplasmic Membrane

• Semipermeable membrane inside the bacterial cell wall.
• Composed of phospholipids and proteins.
• Involved in transport of nutrients and waste.
• Also contains enzymes for respiration and oxidative phosphorylation to make energy.
• Involves DNA replication, cell wall synthesis, and secretion of proteins.

Cytoplasm

• The gelatinous substance inside the cytoplasmic membrane.
• Contains the genetic material (DNA), ribosomes, and other components such as storage granules.
• Prokaryotes lack mitochondria and endoplasmic reticulum.

Ribosomes

• Complex structures within the cytoplasm.
• Made of RNA and proteins.
• Involved in protein synthesis.
• 70S ribosomes are found in prokaryotes.
• 80S ribosomes are found in eukaryotes.

The Nuclear Body

• Contains the cell's genetic material (DNA).
• Organized into a single chromosome.
• Bacterial cells lack a nucleus.

Plasmids

• Extrachromosomal DNA molecules that replicate independently of the bacterial chromosome.

Capsule

• Gelatinous layer outside the cell wall.
• Polysaccharide in most bacteria.
• Aids in adherence, protection, and evasion of the immune system.

Flagella

• Long, whip-like appendages.
• Involved in bacterial motility.
• Can have various arrangements (e.g. monotrichous, lophotrichous, amphitrichous).

Fimbriae (Pili)

• Short, hair-like appendages.
• Important for attachment and conjugation (DNA transfer).

Spores

• The resting or dormant forms in some bacteria.
• High resistance to harsh conditions.
• Produced in response to unfavorable conditions (e.g. lack of nutrients or extreme environmental factors).
• They are responsible for the resistance of bacteria to heat and chemicals.

Glycocalyx

• Thin coat made of polysaccharides.
• Found on the surface of bacteria.
• Helps in adhesion and colonization.