ch_04_lecture_presentation 13 ed edited no videos (1)

Chapter 4: Functional Anatomy of Prokaryotic and Eukaryotic Cells

Comparing Prokaryotic and Eukaryotic Cells: An Overview

• Prokaryote:

  • Greek origin meaning "prenucleus".

  • Characteristics:

    • One circular chromosome, not membrane-bound.

    • No histones or organelles.

    • Bacterial cell walls contain peptidoglycan; Archaea have pseudomurein.

    • Reproduces via binary fission.

• Eukaryote:

  • Greek origin meaning "true nucleus".

  • Characteristics:

    • Paired chromosomes enclosed in a nuclear membrane.

    • Contains histones and organelles.

    • Cell walls (when present) are polysaccharide-based.

    • Reproduces via mitosis.

Identifying Basic Bacterial Shapes

• Bacterial Size and Shape:

  • Average size: 0.2 to 2.0 µm in diameter and 2 to 8 µm in length.

  • Forms:

    • Monomorphic: most bacteria exhibit a single shape.

    • Pleomorphic: some bacteria can change shapes.

• Bacterial Shapes:

  • Bacillus: Rod-shaped.

  • Coccus: Spherical-shaped.

  • Spiral:

    • Vibrio: comma-shaped.

    • Spirillum: spiral-shaped.

    • Spirochete: tightly coiled.

  • Other shapes: Star-shaped, Rectangular.

Arrangements of Cocci and Bacilli

• Cocci Arrangements:

  • Pairs: Diplococci.

  • Clusters: Staphylococci.

  • Chains: Streptococci.

  • Groups of four: Tetrads.

  • Cubelike groups: Sarcinae.

• Bacilli Arrangements:

  • Pairs: Diplobacilli.

  • Chains: Streptobacilli.

  • Shape-specific formations: Single bacillus, Coccobacillus.

Prokaryotic Cell Structure

• Structures External to the Cell Wall:

  • Glycocalyx:

    • Viscous and gelatinous layer made of polysaccharides/polypeptides.

    • Types:

      • Capsule: well-organized and firmly attached.

      • Slime layer: unorganized and loose.

    • Contributes to virulence by preventing phagocytosis and aiding biofilm formation.

  • Flagella:

    • Filamentous appendages for propulsion; made of protein (flagellin).

    • Comprises three parts:

      • Filament: longest part.

      • Hook: connects filament to basal body.

      • Basal Body: anchors flagellum to the cell wall/membrane.

    • Variations in arrangement:

      • Peritrichous: flagella all over the cell.

      • Monotrichous: one flagellum.

      • Lophotrichous: multiple flagella at one end.

      • Amphitrichous: one flagellum at each end.

    • Movement through "run" and "tumble" dynamics based on rotation.

  • Fimbriae: Hair-like appendages for attachment.

  • Pili: Facilitate motility and bacterial conjugation.

The Cell Wall of Prokaryotes

• Main Functions:

  • Prevents osmotic lysis and protects the plasma membrane.

• Composition:

  • Made of peptidoglycan in bacteria, contributing to cell wall integrity.

• Differences Between Types:

  • Gram-positive: Thick peptidoglycan, contains teichoic acid; high susceptibility to penicillin; produces exotoxins.

  • Gram-negative: Thin peptidoglycan, outer membrane present; protects against phagocytosis and antibiotics; produces endotoxins.

Internal Structures of Prokaryotic Cells

• Cytoplasm:

  • Includes water (80%), proteins, carbohydrates, lipids, ions.

• Nucleoid:

  • Contains the bacterial chromosome (circular DNA) and plasmids (extrachromosomal DNA).

• Ribosomes:

  • Sites of protein synthesis; smaller 70S ribosomes compared to eukaryotic 80S ribosomes.

  • Structural composition: 50S and 30S subunits.

• Inclusions:

  • Various storage structures (e.g., metachromatic granules, polysaccharide granules).

• Endospores:

  • Resistant resting cells produced during nutrient depletion for survival.

Eukaryotic Cells Overview

• Major Organelles:

  • Nucleus: Contains DNA, involved in cell division.

  • Endoplasmic Reticulum: Rough ER (protein synthesis with ribosomes) and Smooth ER (lipid synthesis).

  • Golgi Complex: Modifies and packages proteins for secretion.

  • Mitochondria: Powerhouse of the cell, ATP production.

  • Chloroplasts: Site of photosynthesis in plants.

Comparison of Prokaryotic and Eukaryotic Features

• Flagella and Cilia:

  • Differences in structure (e.g., 9 + 2 microtubule arrangement in eukaryotes).

• Cell Wall and Glycocalyx:

  • Prokaryotic cell walls are peptidoglycan-based; Eukaryotic cell walls (when present) are carbohydrate-based.

• Plasma Membrane:

  • Similar structures but differ in the presence of sterols and carbohydrates in eukaryotes.

Summary on the Evolution of Eukaryotes

• Endosymbiotic Theory:

  • Proposes that eukaryotic cells evolved from larger prokaryotic cells engulfing smaller prokaryotic cells, leading to the development of mitochondria and chloroplasts.