Three Domains of Life

Overview

• Life is scientifically divided into three domains:
  • Eukarya
  • Archaea
  • Bacteria
• These domains originated from a common ancestor.
• They did not originate at the same time:
  • Common ancestor mutated to create two domains: Bacteria and a group that further mutated into Archaea and Eukarya.

Classification Systems

• Earlier classification: Five Kingdom System
  • Categories: Monera, Protists, Fungi, Plants, Animals
  • Monera grouped Archaea and Bacteria together.
• New classification: Three Domain System
  • Monera divided into Bacteria and Archaea.
  • Eukarya includes Protists, Fungi, Plants, and Animals.

Domain Details

Eukarya

• Eukaryotic organisms:
  • Can be single or multicellular.
  • Contain membrane-bound nucleus and organelles.
• Examples of membrane-bound organelles:
  • Nucleus
  • Mitochondria
  • Ribosomes
  • Golgi apparatus
  • Endoplasmic reticulum
  • Lysosomes
  • Chloroplasts (in plants)

Archaea

• Characteristics:
  • Single-celled organisms.
  • Share similarities with both Eukaryotes and Bacteria.
• Similarities with Eukaryotes:
  • Start mRNA translation with methionine.
  • Associate DNA with histone proteins.
  • Similar RNA polymerases.
  • Similar DNA replication mechanisms.
  • Share metabolic pathways.
• Similarities with Bacteria:
  • Both are prokaryotes (lack membrane-bound nucleus and organelles).
  • Contain a single circular chromosome.
  • Reproduce via binary fission, budding, and fragmentation.
  • Use flagella for movement.
• Unique characteristics:
  • Known as extremophiles; can withstand extreme conditions (high temperature, pressure, salinity).
  • Found in normal environments (e.g., human skin).
  • Energy sources:
    • Photosynthetic (light, CO2, water)
    • Chemosynthetic (inorganic compounds like ammonia)

Bacteria

• Characteristics:
  • Single-celled, lack membrane-bound organelles.
  • First prokaryotic cells discovered; referred to as eubacteria (true bacteria).
• Relationships with humans:
  • Symbiotic (e.g., gut microbiome):
    • About 1 trillion bacteria in human gut.
    • Beneficial bacteria produce vitamins (e.g., Vitamin K, Biotin).
  • Pathogenic bacteria cause diseases:
    • Can be intracellular (inside cells) or extracellular (outside cells).
    • Classified as Gram-positive or Gram-negative:
      • Gram-negative bacteria are primary pathogens; resistant to antibiotics.
      • Can cause serious conditions like bacterial septic shock.

Conclusion

• Importance of understanding the three domains of life.
• For more information, visit clarifyscienceconcepts.com.
• Encourage questions and engagement in the comments.