Microbiology Lecture Notes: Viruses

Overview

• Examined prokaryotes (bacteria, archaea) and eukaryotes (protists, fungi, lichens, algae, plants, animals)
• Focus on viruses, which require electron microscopes to be seen

Characteristics of Viruses

• Not eukaryotic or prokaryotic as they are not cells
• Composed of a basic set of genes, lacking cell structures like organelles
• No internal compartments, metabolism, ribosomes, or membranes
• Considered ultimate intracellular parasites, needing a host cell for reproduction

Antibiotics and Viruses

• Antibiotics target cell structures; ineffective against viruses
• Limited antiviral drugs available due to viruses' reliance on host cell machinery

Are Viruses Living?

• Debate on whether viruses are living organisms
• Do not fit typical criteria: cannot reproduce independently, lack cellular structure

Virus Structure

• Composed of genetic material (DNA or RNA, not both)
  • Can be single- or double-stranded
• Encased in a protein shell (capsid)
  • Capsids can be helical, polyhedral, or complex

Capsid

• Protein shell housing genetic material
• Some viruses have an additional lipid layer called an envelope
  • Enveloped viruses (e.g., HIV) are easier to control

Virus Specificity and Variety

• Highly specific to host types (e.g., respiratory tract, plants, bacteria)
• Variety in forms, from small bacteriophages to larger viruses

Studying Viruses

• Cannot grow viruses like bacteria; require host cells
• Electron microscopy used to visualize viruses
  • Micrometer to nanometer scale necessary

Examples of Viruses

• Ebola: Large, helical virus
• Adenovirus: Polyhedral, causes respiratory infections
• Tobacco Mosaic Virus: Infects plants
• Bacteriophages: Infect bacteria, not humans

Challenges in Treating Viral Infections

• Drugs must target the virus without harming host cells
• Example: COVID-19 treatments can have side effects due to this difficulty

Conclusion

• Viruses are highly specific and varied
• Not cells, not fitting neatly into categories
• Require careful study and targeted treatment approaches