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Human Viruses: Types, Genome Organization & Functional Diversity Analysis

Dr. Muhammad Shafiq

Department of Biotechnology / Bioinformatics

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What is a Virus?

  • • Obligate intracellular parasite
  • • Contains DNA or RNA genome
  • • Uses host cell machinery for replication
  • • Composed of genome, capsid, and sometimes envelope

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Baltimore Classification of Human Viruses

  • • Group I: dsDNA (Herpesvirus)
  • • Group II: ssDNA (Parvovirus)
  • • Group III: dsRNA (Rotavirus)
  • • Group IV: +ssRNA (SARS-CoV-2)
  • • Group V: -ssRNA (Influenza)
  • • Group VI: ssRNA-RT (HIV)
  • • Group VII: dsDNA-RT (Hepatitis B virus)

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DNA Viruses

  • • Usually replicate in nucleus
  • • More genetically stable
  • • Examples: Herpesvirus, Adenovirus, HPV, Hepatitis B virus
  • • Complex gene regulation mechanisms

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RNA Viruses

  • • High mutation rate
  • • Rapid evolution
  • • Mostly replicate in cytoplasm
  • • Examples: SARS-CoV-2, Influenza virus, HIV, Rabies virus

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Viral Genome Organization

  • • Linear or circular genomes
  • • Segmented genomes (e.g., Influenza)
  • • Overlapping genes
  • • Polyprotein coding strategies

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Gene Organization Strategies

  • • Overlapping reading frames
  • • Alternative splicing
  • • Ribosomal frameshifting
  • • Subgenomic RNAs
  • • Polyprotein cleavage

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Functional Diversity of Viral Genes

  • • Structural proteins (capsid, envelope)
  • • Replication enzymes (polymerases)
  • • Regulatory proteins
  • • Immune evasion proteins
  • • Host interaction factors

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Genome Size Diversity

  • • Parvovirus ~5 kb
  • • HIV ~9.7 kb
  • • Influenza ~13 kb
  • • SARS-CoV-2 ~30 kb
  • • Herpesvirus ~150 kb

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Viral Diversity Analysis (Bioinformatics)

  • • Genome sequencing
  • • Multiple sequence alignment
  • • Phylogenetic analysis
  • • SNP detection
  • • Recombination analysis
  • • Functional domain prediction

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Evolution & Mutation in Viruses

  • • RNA viruses evolve faster
  • • Error-prone RNA polymerase
  • • Drug resistance development
  • • Immune escape & variant emergence

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Applications in Research & Medicine

  • • Vaccine development
  • • Antiviral drug targets
  • • Epidemiological tracking
  • • Functional genomics studies
  • • Pandemic surveillance