Understanding Acellular Pathogens and Viruses ch six

Oct 18, 2024

Lecture Notes: Acellular Pathogens and Viruses

Introduction

  • Chapter 6 focuses on disease-causing agents that are not cells.
  • Main focus: Viruses (also some mention of prions).

Characteristics of Viruses

  • Acellular: Not composed of cells.
  • Obligate Intracellular Parasites: Need to live inside another cell to reproduce.
  • Host Specificity: Narrow range of hosts they can infect, often specific to a species or cell type.
  • Genomic Material: Contain either DNA or RNA, never both.
  • Capsid: Protein coat surrounding the nucleic acid.
  • Envelope: Some viruses have a phospholipid membrane envelope.

Virus Structure

  • Naked Virus: DNA or RNA + capsid.
  • Enveloped Virus: DNA or RNA + capsid + envelope.
  • Spikes: Glycoproteins that enable attachment to host cells.

Viral Shapes

  • Helical
  • Icosahedral
  • Complex

Virus Classification

  • Based on type of nucleic acid:
    • Double-stranded DNA (enveloped/naked)
    • Single-stranded DNA
    • Double-stranded RNA
    • Single-stranded RNA (two types)
  • Replication: Viruses hijack host cellular machinery to replicate.

Viral Life Cycles

  • Lytic Cycle: Results in cell death.
    1. Attachment
    2. Penetration
    3. Biosynthesis
    4. Maturation
    5. Lysis
  • Lysogenic Cycle: Virus integrates into host DNA (prophage), can later enter lytic cycle.
  • Animal Cells: Involves uncoating; viral DNA may integrate into the host nucleus.

Viral Enzymes

  • RNA-dependent RNA Polymerase
  • Reverse Transcriptase: Converts RNA to DNA.

Types of Viral Infections

  • Persistent: Virus remains in tissue (e.g., herpes).
  • Latent: Dormant until activated (e.g., chickenpox -> shingles).
  • Chronic: Symptoms worsen over time (e.g., HIV).

Other Acellular Pathogens

  • Viroids: Plant pathogens.
  • Prions: Infectious protein particles.
    • Cause neurological cell death.
    • Diseases: Kuru, Creutzfeldt-Jakob, mad cow disease.

Key Takeaways

  • Understand virus composition and characteristics.
  • Differentiate replication processes based on DNA/RNA and virus type.
  • Review recommended videos for a better understanding of viral replication and prion diseases.