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Understanding Prokaryotes and Their Characteristics

May 24, 2025

Lecture Notes: Prokaryotes

Introduction

  • Prokaryotes: Organisms without membrane-bound nuclei.
    • Derived from Greek: "pro" (before) + "karyon" (nucleus)
  • Eukaryotes: Organisms with true nucleus.
    • Derived from Greek: "eu" (true) + "karyon" (nucleus)
  • Domains of Life:
    • Bacteria and Archaea: Prokaryotes
    • Eukarya: Eukaryotes

Characteristics of Prokaryotes vs. Eukaryotes

Size

  • Prokaryotes: 0.2 to 2 micrometers in diameter
  • Eukaryotes: 10 to 100 micrometers in diameter

Nucleus

  • Prokaryotes: No nuclear membrane/nuclei; have nucleoid region and single circular chromosome.
  • Eukaryotes: True nucleus with nuclear membrane and multiple linear chromosomes.

Organelles

  • Prokaryotes: No membrane-bound organelles.
  • Eukaryotes: Membrane-bound organelles (e.g., lysosomes, Golgi apparatus, ER).

Movement

  • Prokaryotic Flagella: Rotary motion with two protein building blocks.
  • Eukaryotic Flagella: Complex, undulatory motion with microtubules.

Glycocalyx

  • Prokaryotes: Capsule or slime layer for protection.
  • Eukaryotes: Present in some cells lacking a cell wall.

Cell Wall

  • Prokaryotes: Chemically complex, contains peptidoglycan.
  • Eukaryotes: Chemically simple; cellulose in plants, chitin in fungi.

Plasma Membrane

  • Prokaryotes: No carbohydrates/sterols.
  • Eukaryotes: Contains sterols and carbohydrates for receptors.

Cytoplasm

  • Prokaryotes: No cytoskeleton or cytoplasmic streaming (cyclosis).
  • Eukaryotes: Cytoskeleton present, allows for cytoplasmic streaming.

Chromosome

  • Prokaryotes: Single circular chromosome, no histones.
  • Eukaryotes: Multiple linear chromosomes, associated with histones.

Cell Division

  • Prokaryotes: Binary fission; no mitotic phases or spindle apparatus.
  • Eukaryotes: Mitosis.

Sexual Reproduction

  • Prokaryotes: No meiosis; DNA transfer via conjugation.
  • Eukaryotes: Involves meiosis.

Prokaryotic Structure

  • Fimbriae: Hairlike appendages for adherence.
  • Capsule: Sticky layer for adherence and immune evasion.
  • Flagella: Rotary motion, different structure from eukaryotes.
  • Sex Pili: Facilitates conjugation and lateral gene transfer.
  • Plasmids: Small DNA rings, often conferring antibiotic resistance.

Reproduction and Adaptation

  • Rapid reproduction through binary fission.
  • Endospores: Dormant cells that can remain viable for centuries.
  • Mutations: Source of genetic variation, driving evolution and antibiotic resistance.
  • Genetic Recombination: Increases diversity, involves lateral gene transfer.

Nutrition and Metabolic Adaptations

  • Greatest diversity in modes of nutrition among life forms.
  • Nutritional Modes:
    • Photoautotrophs: Light as energy source; use CO2 as carbon source.
    • Chemoautotrophs: Inorganic chemicals as energy source; use CO2 as carbon source.
    • Photoheterotrophs: Light as energy source; use organic compounds as carbon source.
    • Chemoheterotrophs: Organic compounds as both energy and carbon source.

Examples

  • Photoautotrophs: Cyanobacteria, plants, certain protists.
  • Chemoautotrophs: Prokaryotes in hydrothermal vents, volcanic areas.
  • Photoheterotrophs: Aquatic and salt-loving prokaryotes.
  • Chemoheterotrophs: Many prokaryotes, fungi, animals, some plants (e.g., carnivorous plants supplementing with insects).

Extremophiles

  • Thermophiles: Thrive in very hot environments.
  • Halophiles: Thrive in high salt environments.

These notes capture the essential details from the lecture on prokaryotes, focusing on their characteristics, structure, reproduction, adaptation, nutrition, and examples of various types.

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