Prokaryotic Cells

Prokaryotic Cells

Overview of Prokaryotes

• Prokaryotes represent 2 of the three domains of life:
  • The Domain Bacteria
  • The Domain Archaea

Ecological Roles

• Metabolic activities of prokaryotes are crucial for maintaining Earth's biosphere.
• Key roles in recycling essential elements:
  • Carbon (C): Break down organic material in dead organisms, releasing $CO_2$.
  • Nitrogen (N): Fix $N_2$ from the atmosphere.
  • Oxygen (O): Produce significant amounts of $O_2$.

Unique Ice-Forming Bacteria: Pseudomonas Syringae

• Found in diverse environments, including soil and clouds.
• Manipulates forces between water molecules to aid ice formation under unusual conditions.
• Utilizes proteins to create high and low-density patches of water, leading to ice formation at higher temperatures.
  • Applications: Used by ski resorts for artificial snow production.
  • Can also cause frost damage to crops.
• May influence weather patterns through its widespread presence and unique functionalities.

Mechanisms of Ice-Making

• Spectroscopy: Used to analyze molecular vibrations of bacteria and water.
• Ordered water structure around P. syringae enhances freezing conditions.
• Identified proteins that lead to the rearrangement of water molecules into crystalline structures for ice formation.

Importance of Prokaryotes in Human Health

• Many prokaryotes are beneficial:
  • E.g., gut bacteria that aid digestion.
• Antibiotics target bacterial pathogens but do not affect eukaryotic cells due to fundamental differences in cell structure.

Characteristics of Prokaryotic Cells

• Size: Very small compared to eukaryotic cells (up to 10 times smaller in diameter).
• Shapes:
  • Cocci: spherical (e.g., Streptococcus).
  • Bacilli: rod-shaped (e.g., Escherichia coli).
  • Spirilla: spiral (e.g., corkscrew shape).

Cell Structure

• Cell Wall: Composed mainly of peptidoglycan, important for rigidity and protection.
  • Gram Staining: Distinguishes between Gram-positive (purple/blue) and Gram-negative (pink) due to differences in cell wall composition.
• Glycocalyx: External layer that can be a slime layer (loose) or capsule (firmly attached).
  • Protects from physical damage and helps in attachment.

Metabolism and Energy Acquisition

• Prokaryotes display metabolic versatility:
  • Categorized by how they respond to oxygen:
  • Aerobes: Require oxygen.
  • Anaerobes:
    • Obligate Anaerobes: Oxygen is toxic; they rely on fermentation.
    • Facultative Anaerobes: Can use oxygen or ferment.

Nitrogen Fixation

• Prokaryotes are essential for nitrogen fixation, converting $N<em>2$ to $NH</em>3$, a vital process for all living organisms.
• Examples of nitrogen-fixing bacteria include Azotobacter and Rhizobium.

Reproduction Methods

1. Binary Fission: Parent cell divides into two identical daughter cells.
2. Conjugation: Exchange of plasmids between two bacteria during mating.
3. Endospores: Some bacteria form dormant cells to survive unfavorable conditions.

Domains of Prokaryotes

• Bacteria:

  • Diverse includes pathogenic species (e.g., Bacillus anthracis, Staphylococcus aureus) and beneficial species (e.g., Lactobacillus).

• Archaea:

  • Known for extremophiles, living in harsh environments (e.g., hot springs).

Antibiotic Mechanisms

• Several classes of antibiotics target specific prokaryotic structures:
  • Protein Synthesis Inhibitors (e.g., Erythromycin targeting the 50S subunit).
  • Cell Wall Inhibitors (e.g., Penicillins).
  • DNA/RNA Synthesis Inhibitors (e.g., Quinolones).
• Mechanisms of resistance include:
  • Drug efflux pumps, inactivation of drugs, or modification of drug target sites.

Conclusion

• Prokaryotes maintain ecological balance and are essential for various biological processes. Understanding their unique characteristics and functions is crucial for medical and environmental applications.