Lecture Notes: Prokaryotic and Eukaryotic Cells

Overview

• Focus on prokaryotic cells in microbiology.
• Eukaryotic cells are more complex, often covered more in general biology.

Prokaryotic Cells

• Characteristics:

  • Simple structure, oldest cell type, precursor to eukaryotic cells.
  • Lack nucleus and organelles like mitochondria.
  • Have DNA, metabolism, generative properties, homeostasis.

• Common Features with Eukaryotic Cells:

  • DNA, ribosomes (site for protein synthesis), cytoplasm, plasma membrane.

• Bacterial Cell Wall:

  • Provides shape and protection.
  • Differs from eukaryotic cell walls (plants/fungi).
  • Made of peptidoglycan.

Bacterial Shapes

• Cocci: Spherical (e.g., coccus, cocci).
• Bacilli: Rod-shaped (e.g., bacillus, bacilli).
• Vibrio: Comma-shaped.
• Spirillum: Wavy.
• Spirochete: Corkscrew.

Bacterial Arrangements

• Mono: Single.
• Diplo: Pairs.
• Strepto: Chains.
• Tetrad: Groups of four.
• Staph: Clusters (like grapes).

Bacterial Diseases

• Leptospirosis: Caused by spirochetes, transmitted through contaminated urine.
• Cholera: Caused by vibrio, transmitted through contaminated water.

Cell Wall Differences

• Gram Positive:

  • Thick peptidoglycan layer, retains purple stain.
  • Contains teichoic acid.

• Gram Negative:

  • Thin peptidoglycan, outer membrane.
  • Contains lipopolysaccharide (LPS), can cause endotoxic shock.

• Acid-Fast Bacteria:

  • Thick lipid layer (mycolic acid), resists staining.
  • Examples: Tuberculosis, leprosy.

Bacterial Structures

• Internal Structures:

  • Cytoplasm, ribosomes (70S), nucleoid region (circular DNA).
  • Some bacteria have plasmids, chromatophores, inclusions, endospores.

• External Structures:

  • Pili: Conjugation and attachment.
  • Glycocalyx: Capsule or slime layer for protection and adherence.
  • Flagella: Movement, various configurations (monotrichous, amphitrichous, etc.).

Bacterial Movement

• Chemotaxis: Movement towards/away from chemical signals.
• Flagella move in counterclockwise (run) or clockwise (tumble).

Eukaryotic Cells and Endosymbiosis

• Eukaryotic Cells:

  • More complex, contain organelles like nucleus, mitochondria, etc.

• Endosymbiotic Theory:

  • Mitochondria and chloroplasts evolved from engulfed prokaryotic cells.
  • Evidence: Size, circular DNA, ribosomes, division method, double membrane.

Cell Surface Area to Volume Ratio

• Importance:

  • Efficient exchange with environment, nutrient intake, waste elimination.

• Mechanisms:

  • Maintain small size, elongate or flatten, folding, compartmentalization.

Summary

• Prokaryotic cells are simpler but essential biological units.
• Understanding their structures and functions is key in microbiology and recognizing bacterial diseases.
• Prokaryotic and eukaryotic cells have distinct differences but also share some similarities.