Bio1400.Ch-27.Fall24

General Information

  • Course: General Biology II (Bio - 1400)

  • Schedule: Fall 2024, Tues/Fri 11:00am – 12:15 pm

  • Instructor: Dr. Indrani Mukherjee

  • Chapter: 27

Introduction to Prokaryotes

  • Domains: Two domains of prokaryotes: Bacteria & Archaea

  • Habitat: Prokaryotes thrive in diverse conditions, including acidic, salty, cold, or hot environments.

  • Size & Numbers: Most prokaryotes are microscopic, yet there are more in a handful of soil than all humans that have ever lived.

  • Evolution: Prokaryotes evolve quickly due to short generation times.

Characteristics of Life

  • Domains of Life: Life categorized into 3 domains: Archaea, Bacteria, Eukaryota.

  • Cell Types:

    • Prokaryotic: Archaea, Bacteria

    • Eukaryotic: Animal, Plant, Fungi, Protists

  • Nuclear Envelope:

    • Prokaryotic cells lack a nuclear envelope; Eukaryotic cells possess one.

  • Gene Structure:

    • Histone proteins are absent in prokaryotes but present in eukaryotes.

  • Cell Wall Composition:

    • Prokaryotic: Peptidoglycan in bacteria; polysaccharides in archaea.

    • Eukaryotic: Cellulose or chitin in plants/fungi.

Structural and Functional Adaptations

  • Distribution: Prokaryotic adaptations contribute to success, including unicellularity and survival in extreme environments.

  • Shapes of Prokaryotic Cells:

    • Cocci (spherical)

    • Bacilli (rod-shaped)

    • Spirillum (spiral)

Cell-Surface Structures

  • Cell Wall:

    • Maintains shape and protects from bursting in hypotonic conditions.

    • Eukaryotic cell walls made of cellulose/chitin; archaean walls lack peptidoglycan.

  • Gram Staining:

    • Classifies bacteria based on cell wall composition.

    • Gram-positive: Thick peptidoglycan layer, stains purple.

    • Gram-negative: Thinner peptidoglycan, outer membrane, stains pink.

Prokaryotic Motility

  • Taxis: Movement in response to stimuli (e.g., chemotaxis).

  • Flagella: Composed of varying proteins; differ among bacteria, archaea, and eukaryotes.

Internal Organization in Prokaryotes

  • Cell Structure:

    • Lack complex compartmentalization but possess specialized membranes.

  • Chromosome Structure:

    • Usually a single circular chromosome located in the nucleoid region.

    • Lack nuclear envelope; replication differs from eukaryotes.

Genetic Variation in Prokaryotes

  • Asexual Reproduction: Binary fission allows quick reproduction, resulting in genetically identical offspring.

  • Mutation: Low rates during fission can lead to significant genetic variation due to rapid reproduction.

  • Genetic Recombination:

    • Horizontal Gene Transfer: Contributes to diversity; mechanisms include transformation, transduction, and conjugation.

Nutritional & Metabolic Adaptations

  • Autotrophs: Require inorganic compounds (e.g., CO2).

    • Heterotrophs: Require organic compounds as nutrients.

  • Oxygen Variation:

    • Obligate aerobes need oxygen; obligate anaerobes are poisoned by it; facultative anaerobes can survive in both conditions.

Role of Prokaryotes in Ecosystems

  • Ecological Importance: Essential for recycling chemical elements.

  • Symbiosis: Involves mutualism (both organisms benefit), commensalism (one benefits without harming the other), and parasitism (one harms the other).

Impacts on Humans

  • Beneficial Prokaryotes: Many assist in digestion, producing vitamins and nutrients.

  • Pathogenic Prokaryotes: Cause diseases via exotoxins and endotoxins.

  • Biotechnological Applications: Used in bioremediation, genetic engineering for producing various compounds.

Conclusion

Prokaryotes are indispensable to life on Earth and play critical roles in ecological balance and human health.