Lecture Notes: Functional Anatomy of Prokaryotic and Eukaryotic Cells

Introduction

• Comparison of prokaryotic and eukaryotic cells
• Focus on prokaryotes, specifically the domain Bacteria

Prokaryotic Cells

DNA Structure

• DNA found in nucleoid (not membrane-bound)
• Single circular chromosome

Organelles

• Lack membrane-bound organelles
• Possess ribosomes (70s structure) for protein synthesis

Cell Wall

• Contains peptidoglycan
• More complex than eukaryotic cell walls
• Eukaryotic cells:
  • Animal cells: No cell wall
  • Plant cells: Cellulose
  • Fungi: Chitin

Cell Division

• Asexual reproduction via binary fission
• Results in identical daughter cells

Cell Organization

• Generally smaller and simpler
• Typically unicellular organisms

Eukaryotic Cells

• More complex structure with multiple organelles
• Generally larger (10x the size of prokaryotes)
• Mostly multicellular organisms (with exceptions in Protista)

Types of Bacteria

Cell Shapes

1. Coccus: Round cells
2. Bacillus: Rod-shaped cells
3. Spirillum: Spiral-shaped cells
4. Vibrio: Comma-shaped cells

Cell Arrangements

• Diplo: Pairs
• Strepto: Chains
• Tetrad: Groups of four
• Sarcinae: Cubical packets
• Staphylococci: Grape-like clusters

Gram Reaction

• Gram-positive: Purple, thicker peptidoglycan layer
• Gram-negative: Pink, thinner peptidoglycan, outer lipopolysaccharide layer
• Importance of identifying gram reaction for classification

Structures in Bacteria

Glycocalyx

• Can be a capsule (firmly attached) or slime layer (loosely attached)
• Protects from immune response and increases virulence

Flagella

• For motility, associated with H antigen
• Types:
  • Peritrichous: Many flagella all over
  • Monotrichous: One flagellum at one end
  • Lophotrichous: Many flagella at one end
  • Amphitrichous: Flagella at both ends

Fimbriae and Sex Pilus

• Fimbriae: Adhesion and attachment (200-400 per cell)
• Sex Pilus: Genetic information transfer (fewer in number)

Cell Wall

• Protects plasma membrane and provides shape
• Gram-positive: Thick peptidoglycan
• Gram-negative: Thin peptidoglycan + lipopolysaccharides (endotoxins)
• Endotoxins can cause severe immune responses

Special Bacteria Types

• Mycoplasma: No cell wall, high lipid content
• Mycobacterium: High lipid content with mycolic acid (requires acid-fast staining)

Plasma Membrane

• Fluid mosaic model: phospholipid bilayer with embedded proteins
• Selectively permeable for transport of substances

Transport Mechanisms

• Active Transport: Requires ATP, moves substances against concentration gradients
• Passive Transport: No energy required, moves substances from high to low concentration
  • Simple Diffusion: Direct movement through membrane
  • Facilitated Diffusion: Movement through transport proteins
  • Osmosis: Movement of water across membrane

Tonicity

• Hypertonic: Cell shrinks (water leaves)
• Hypotonic: Cell swells (water enters, risk of bursting)
• Isotonic: No net movement of water

Cytoplasm and Ribosomes

• Cytoplasm: Mostly water, contains nucleoid and ribosomes
• Ribosomes: Two subunits (30s + 50s = 70s in prokaryotes)
• Antibiotics can target bacterial ribosomes (70s) without affecting human ribosomes (80s)

Endospores

• Dormant, metabolically inactive structures for survival in harsh conditions
• Examples: Clostridium species (causes botulism, tetanus)

Important Implications

• Food preservation and sterilization practices
• Importance of vaccines and public awareness about bacterial infections and prevention.