Microbiology Overview on Cells

Study Notes

Microorganisms are classified into acellular (viruses) and cellular organisms (prokaryotes and eukaryotes).

Prokaryotes lack a true nucleus, while eukaryotes have a defined nuclear body.
Prokaryotic cells divide through binary fission; eukaryotic cells divide via mitosis or meiosis.
Prokaryotes typically have peptidoglycan cell walls; eukaryotic cells may have cellulose or chitin.
Prokaryotic cytoplasmic membranes are simpler than eukaryotic ones.
Prokaryotes generally lack membrane-bound organelles, whereas eukaryotes contain them.
Energy production in prokaryotes occurs in the cytoplasmic membrane; in eukaryotes, it occurs in mitochondria.
Protein synthesis sites differ; prokaryotes use ribosomes in the cytoplasm, while eukaryotes use ribosomes attached to the endoplasmic reticulum.

Cell Wall: Composed mainly of peptidoglycan, providing protection and shape to bacteria. Components like M protein and mycolic acid can enhance pathogenicity.
Cytoplasmic Membrane: Functions as a selectively permeable barrier.
Mesosomes: Extensions of the cytoplasmic membrane, serving as sites for chromosome attachment.
Ribosomes: Essential for protein synthesis.
Inclusions: Nutrient storage, with examples including metachromatic granules.
Endospores: Highly resistant resting cells composed of calcium dipicolinate, produced by genera like Bacillus and Clostridium.
Capsule: Enhances virulence by hindering phagocytosis; can be antigenic based on K antigens.
Pili (Fimbriae): Include ordinary pili for attachment and sex pili for conjugation.
Glycocalyx: Can be a capsule (organized) or slime layer (unorganized).

Flagella: Used for locomotion; classified by arrangements (atrichous, monotrichous, etc.).
Periplasmic Flagella: Also known as axial filaments, contribute to cell motility.

Adherence and antiphagocytic factors, enzymes, and toxins (exotoxins and endotoxins) play significant roles in pathogenicity.
Exotoxins: Secreted proteins, heat-labile, with specific pharmacological effects.
Endotoxins: Part of the bacterial cell wall, heat-stable, less immunogenic.

Nutrients: Essential elements like carbon, nitrogen, and minerals are necessary for growth.
- Some organisms are halophilic, requiring high salt concentrations.
Oxygen and Carbon Dioxide:
- Obligate aerobe: Requires oxygen.
- Obligate anaerobe: Grows in absence of oxygen.
- Facultative anaerobe: Can switch between aerobic and anaerobic respiration.
- Microaerophilic: Requires low oxygen levels.
- Capnophilic: Prefers elevated CO2 levels.
Temperature: Bacteria can be classified as psychrophilic, mesophilic, or thermophilic based on optimal temperature ranges.
pH: Most bacteria thrive in neutral or slightly alkaline conditions; some extremes include acidophiles and alkaliphiles.

Understanding bacterial growth cycles is essential for proper culturing and experimentation.
Nutrient media formulation is critical for cultivating specific microorganisms.