Lecture Notes: Chapter 27 - Bacteria and Archaea

Overview

• Focus on Bacteria and Archaea, both are prokaryotes.
• Prokaryotes are the most abundant organisms on Earth.
• Prokaryotes are single-celled organisms and belong to two domains: Bacteria and Archaea.
• Humans (eukaryotes) belong to the domain Eukarya.

Key Differences: Prokaryotes vs. Eukaryotes

• Prokaryotes: No nucleus, no membrane-bound organelles.
• Eukaryotes: Have a nucleus and membrane-bound organelles.
• Prokaryotes include bacteria and archaea.

Characteristics of Prokaryotes

• Size: Extremely small, microscopic.
• Reproduction: Reproduce via binary fission (asexual reproduction) leading to rapid population growth.
• Mutation Rate: While individual mutation rates are low, large populations and rapid reproduction increase genetic diversity.
• Adaptations: Thrive in diverse and hostile environments (e.g., hot springs).

Structural Features

• Cell Wall: Maintains shape, protects cell, prevents bursting in hypotonic environments.
  • Bacteria: Cell walls contain peptidoglycan.
  • Archaea: Lack peptidoglycan in cell walls.
• Types of Bacteria Cell Walls:
  • Gram-positive: Thick peptidoglycan layer.
  • Gram-negative: Thin peptidoglycan, more complex, includes lipopolysaccharides.

Medical Relevance

• Gram Staining: Differentiates between gram-positive and gram-negative bacteria; affects treatment strategies.
• Antibiotics: Target bacterial cell walls (peptidoglycan), ineffective against viruses.

Additional Structures

• Capsule: Dense, sticky layer outside cell wall aiding in adherence.
• Endospores: Resistant cells for surviving harsh conditions, can remain dormant for centuries.
• External Features:
  • Flagella: Tail-like structures for movement.
  • Pillai: Appendages for DNA transfer.
  • Fimbriae: Hair-like structures for adherence.

Genetic Material

• Nucleoid: Region in cytoplasm where DNA is located, not membrane-bound.
• Chromosomes: One round chromosome in prokaryotes.
• Plasmids: Small rings of DNA, independently replicating.

Reproduction and Adaptation

• Binary Fission: Asexual reproduction method.
• Rapid Evolution: Due to high reproduction rate, mutations, and large population size.
• Mutation: Rare per gene but significant due to population size and reproduction rate.

Conclusion

• Prokaryotes, though simpler in structure, are not primitive.
• Their ability to adapt rapidly makes them successful organisms.
• Despite their simplicity, they play crucial roles in various ecosystems and can be both beneficial and harmful to humans.

Note: The lecture will continue in Part 2.