Lecture Notes: Chapter 4 - Prokaryotic Cell Structure and Function

Overview

• Types of Microbes: Prokaryotes, Eukaryotes, Viruses
• Focus on Prokaryotes in this chapter

History of Prokaryotes

• Development of the microscope by Hooke and refinement by Van Leeuwenhoek
• Initial observations:
  • Large cells with a "kernel" (nucleus) – Eukaryotes
  • Small cells without a kernel – Prokaryotes
• Prokaryotes were initially thought to mature into Eukaryotes, but they are distinct organisms.

Characteristics of Prokaryotic Organisms

• Size: Very small compared to Eukaryotic cells
• Organelles: No organelles
• Unicellular: Composed of only one cell
• Metabolism:
  • Heterotrophic: Ingest other organisms for carbon and energy
  • Autotrophic: Produce organic carbon via photosynthesis
• Reproduction: Asexual

Classification of Prokaryotes

• Two Groups: Bacteria and Archaea
  • Bacteria: Often divided into Gram-positive and Gram-negative
  • Archaea:
    • Ancient organisms
    • No peptidoglycan in cell walls
    • Extremophiles (e.g., Halophiles, Thermophiles, Acidophiles)

Importance of Identification

• Identification critical in medicine
• Unknown project involves identifying a sample of bacteria
• Bacterial Shapes:
  • Coccus: Round
  • Bacillus: Rod
  • Spiral: Curved or spiraled
• Bacterial Arrangements:
  • Coccus: Diplococci, Streptococci, Tetrad, Sarcinae, Staphylococci
  • Bacilli: Single, Diplobacilli, Streptobacilli, Coccobacilli
  • Spiral: Vibrio, Spirillum, Spirochete

Prokaryotic Cell Structure

• Compared to Eukaryotes
• Identification and Pathogenicity

External Structures

• Appendages:
  • Flagella: Used for locomotion; structure includes H antigens
  • Fimbriae: Used for attachment
  • Pilus: Used for DNA transfer during conjugation

Cell Layers

• Glycocalyx:
  • Slime Layer: Unorganized, loosely attached
  • Capsule: Organized, tightly attached, increases pathogenicity
• Cell Wall: Protects from osmotic lysis
  • Gram-positive: Thick peptidoglycan layer
  • Gram-negative: Thin peptidoglycan with outer membrane, Lipopolysaccharides (LPS)
  • Acid-fast: Little peptidoglycan, many lipids (e.g., Mycobacterium)
• Cell Membrane: Phospholipid bilayer, selectively permeable

Internal Structures

• Cytoplasm: Includes cytosol, ribosomes, and potentially plasmids and inclusions
• Chromosome: Single, circular DNA
• Ribosomes: 70S in prokaryotes, essential for protein synthesis
• Plasmids: Small DNA molecules, confer antibiotic resistance
• Inclusions: Storage areas within the cell

Endospores

• Produced by Bacillus and Clostridium
• Highly resistant resting cells
• Process: Sporulation
• Resistant to disinfection, heat, radiation

Conclusion

• Review structures and their roles in identification and pathogenicity
• Consider differences and similarities between prokaryotic and eukaryotic cells for further understanding.