Viruses and Viroids Overview

Viruses

• Definition: Viruses are microscopic infectious agents that require a living host cell to replicate.
• Structure: Composed of genetic material (DNA or RNA) surrounded by a protein coat (capsid); some have an outer lipid envelope.
• Reproduction: Hijack host cellular machinery to reproduce; can follow lytic (destructive) or lysogenic (integrative) cycles.
• Classification: Classified based on:
  • Type of nucleic acid (DNA or RNA)
  • Presence of an envelope
  • Shape (icosahedral, helical, complex)
• Diseases: Cause numerous diseases in humans, animals, and plants (e.g., influenza, HIV, COVID-19).

Viroids

• Definition: Small, circular RNA molecules that infect plants, lacking a protein coat.
• Characteristics:
  • The smallest known infectious pathogens
  • Only consist of a short strand of RNA
  • Replicate within host cells using host's own machinery
• Associated Diseases: Cause various plant diseases (e.g., potato spindle tuber disease).

Prions

• Definition: Infectious agents composed solely of misfolded proteins; lack nucleic acids.
• Mechanism: Induce normal proteins in the brain to misfold, leading to brain damage and disease.
• Characteristics:
  • Resistant to heat and proteases
  • Cause neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease, BSE - "mad cow disease").
• Transmission: Can be transmitted through contaminated food or medical procedures.

Lichen

• Definition: Symbiotic association between fungi (mycobiont) and photosynthetic organisms (photobiont, usually algae or cyanobacteria).
• Characteristics:
  • Grow in diverse environments (rocks, trees, soil).
  • Serve as indicators of air quality and environmental health.
  • Can reproduce sexually (fungal spores) or asexually (fragmentation, soredia).
• Role in Ecosystems:
  • Contribute to soil formation and nutrient cycling.
  • Serve as food for various organisms and habitat for small fauna.

Viruses

• Microscopic infectious agents requiring a living host cell to reproduce.
• Composed of genetic material (DNA or RNA) encased in a protein coat (capsid), with some having an outer lipid envelope.
• Replicate by hijacking host cellular machinery, following lytic (destructive) or lysogenic (integrative) cycles.
• Classified based on their nucleic acid type (DNA or RNA), presence of an envelope, and shape (icosahedral, helical, complex).
• Viruses cause various diseases in humans, animals, and plants, such as influenza, HIV, and COVID-19.

Viroids

• Small, circular RNA molecules lacking a protein coat that infect plants.
• The smallest known infectious pathogens, consisting only of a short strand of RNA.
• Replicate within host cells using the host's own machinery.
• Cause various plant diseases, like potato spindle tuber disease.

Prions

• Infectious agents made solely of misfolded proteins, lacking nucleic acids.
• Induce normal proteins in the brain to misfold, leading to brain damage and disease.
• Resistant to heat and proteases.
• Cause neurodegenerative diseases such as Creutzfeldt-Jakob disease and Bovine Spongiform Encephalopathy (BSE, "mad cow disease").
• Transmitted via contaminated food or medical procedures.

Lichens

• Symbiotic association between fungi (mycobiont) and photosynthetic organisms (photobiont, typically algae or cyanobacteria).
• Grow in diverse environments, including rocks, trees, and soil.
• Serve as indicators of air quality and environmental health.
• Reproduce sexually through fungal spores or asexually through fragmentation and soredia.
• Contribute to soil formation and nutrient cycling within ecosystems.
• Provide food for various organisms and habitat for small fauna.

Explore the fascinating world of viruses and viroids in this quiz. Learn about their structure, reproduction, classification, and the diseases they cause. Test your knowledge on how these infectious agents impact humans, animals, and plants.