Microbial World Chapter 01

Viruses

• Not classified as prokaryotes or eukaryotes due to reliance on host for survival.
• Reproduce only by using cellular machinery of other organisms.
• Considered living only when multiplying within host cells; cannot survive outside living hosts.

Bacteria and Classification

• Classified as prokaryotes due to lack of membrane-bound organelles and nucleus.
• Cell wall contains peptidoglycan, a unique feature.
• Archaea are also prokaryotes but lack peptidoglycan in their cell walls.
• Fungi, plants, and protists are classified as eukaryotes and have membrane-bound nuclei.

Characteristics of Organisms

• Algae are photosynthetic eukaryotes.
• Prokaryotes, including bacteria and archaea, lack a membrane-bound nucleus and organelles.
• Bacteria reproduce via binary fission, not mitosis.
• True fungi have chitin in cell walls, while plant and algal walls contain cellulose.

Genetic Material

• All living organisms contain DNA; it's not a distinguishing feature between domains.
• Bacteria have both DNA and RNA; viruses contain either DNA or RNA.
• Bacterial cell walls are made of peptidoglycan, which is absent in archaea.

Theoretical Understanding

• The theory of biogenesis states that living cells arise from preexisting cells.
• Viruses are only considered living when they replicate within host cells.

Archaea

• Do not typically cause diseases in humans and include groups like methanogens and extreme halophiles.
• Not all archaea possess cell walls, differentiating them from bacteria.

Summary of Cellular Structures

• Bacteria are not eukaryotes; they are prokaryotic and lack membrane-enclosed structures.
• Eukaryotes (algae, helminthes, fungi, protozoa) possess membrane-enclosed organelles and nuclei.