Prokaryotes Overview

Overview of Prokaryotes

  • Prokaryotes include Domains Bacteria and Archaea.
  • Both these domains share specific features typical to prokaryotic cells.

Basic Classification

  • Domain Bacteria: Refers to organisms belonging to the Kingdom Bacteria.
  • Domain Archaea: Refers to organisms belonging to the Kingdom Archaea.

Prokaryote Shapes

  • Prokaryotes can have three basic shapes:
    • Spherical (Cocci)
    • Rod-shaped (Bacilli)
    • Spiral (helical forms)

Prokaryote Cell Surface

  • Most prokaryotes possess:
    • Plasma membrane
    • Cell wall: Provides protection against hypotonic conditions.
Cell Wall Composition
  • Bacteria: Composed of Peptidoglycan, a polysaccharide with polypeptide cross-linkages.
  • Archaea: Composed of various polysaccharides and proteins (different from those seen in bacteria).
Gram Stain Classification
  • Gram-positive Bacteria:
    • High concentration of peptidoglycan that traps crystal violet, appearing purple in color.
  • Gram-negative Bacteria:
    • Complex cell walls with lower concentrations of peptidoglycan, appear red due to the crystal violet rinse away.
Additional Cell Structures
  • Capsule: An additional layer of polysaccharides or proteins present in many prokaryotes that aids in protection.
  • Fimbriae: Hair-like appendages aiding in adhesion to substrates.
  • Flagella: Structure for motility, typically composed of:
    • Motor
    • Hook
    • Filament

Prokaryote Internal Organization

  • Nucleoid: Concentrated area where a prokaryote’s circular DNA is located.
  • Plasmids: Smaller rings of DNA found in some bacteria.

Prokaryote Reproduction

  • Binary Fission: Method of division; allows rapid reproduction and adaptation.
  • Remarkably, there are approximately 5 x 10^30 prokaryotic individuals on Earth!

Diversity of Prokaryotes

  • Prokaryotes are incredibly diverse, but specific unfamiliar species do not need to be memorized.
    • Significant groups include Escherichia coli, Chlamydia trachomatis, Streptomyces sp., Borrelia burgdorferi, Cyanobacteria.

Domain Archaea

  • Methanogens: Produce methane as a byproduct.
  • Extreme Thermophiles: Thrive in extremely hot environments.
  • Extreme Halophiles: Flourish in highly saline environments.

Genetic Recombination in Prokaryotes

  • Transduction: Phages transfer bacterial DNA from one host to another.
  • Transformation: Uptake of foreign DNA from the surroundings.
  • Conjugation: DNA exchange between individuals of the same species.

Prokaryote Nutrition

  • Diverse modes of obtaining energy and nutrients:
    • Photoautotrophs: Use light for energy (Ex: Cyanobacteria).
    • Chemoautotrophs: Utilize inorganic chemicals.
    • Heterotrophs: Depend on organic compounds for energy.

Oxygen Usage in Prokaryotes

  • Prokaryotes can be classified based on their oxygen requirements:
    • Obligate Aerobes: Require oxygen for cellular respiration.
    • Obligate Anaerobes: Poisoned by oxygen.
    • Facultative Anaerobes: Can survive with or without oxygen.

Prokaryotes and the Nitrogen Cycle

  • Nitrogen fixation: Some bacteria can convert Nitrogen gas (N₂) into usable forms like ammonium (NH₃).

Metabolic Cooperation

  • Cooperation between prokaryotes can enhance resource use efficiency, exemplified by Cyanobacteria Anabaena, which combines photosynthetic and nitrogen-fixing cells.
  • Biofilms: Surface-coating colonies highlighting cooperative behavior among prokaryotes.

Human Pathogens from Prokaryotes

  • Some diseases caused by prokaryotes:
    • Bacterial dysentery
    • Cholera
    • Typhoid
    • Gonorrhea
    • Syphilis
    • Tuberculosis
    • Acne, and many others.

Antibiotic Mechanisms

  • Antibiotics can work through various mechanisms:
    • Disrupting peptidoglycan formation.
    • Disrupting ribosomal function.
    • Damaging plasma membranes.
    • Interrupting DNA replication and transcription.

Comparative Characteristics Among Domains

  • Bacteria vs Archaea vs Eukarya:
    • Membrane-bound nucleus: No (Bacteria, Archaea), Yes (Eukarya)
    • Histones: No (Bacteria), Yes (Archaea, Eukarya)
    • Peptidoglycan: Yes (Bacteria), No (Archaea, Eukarya)
    • Ribosome mass: 70s (Bacteria, Archaea), 80s (Eukarya)

Questions for Review

  • Key differences between eukaryotic and prokaryotic cells.
  • Explain the significance of DNA location in prokaryotes.
  • What are the methods of genetic exchange in prokaryotes?
  • Examine the various roles of prokaryotes in human health and disease.

Conclusion

  • Prokaryotes represent a crucial part of the biosphere and human health, showcasing a remarkable array of adaptations and diversity.