Viral Structure and Replication
1. Viral Structure
Hepadnaviruses
Enveloped
Virus Particle: Contains ds/ssDNA, unusual
Covering-Capsid: Protein coat surrounded by capsomers.
Envelope: (Not found in all viruses).
Central Core – Nucleic Acid Molecules: (DNA or RNA) Double/single strand DNA/RNA, every viron has it.
Matrix Proteins: Enzymes not found in all viruses.
HepB
- Break in skin/blood, STD
- Flu-like symptoms, jaundice
2 Shapes
- Helical
- Icosahedral
Non-Enveloped Viruses
Adenoviruses/Papillomaviruses/Polyomaviruses/Parvoviruses
Adeno
- Infect lymphoid tissue
- Respiratory/intestinal tissue
Papillo
- HPV, warts, direct contact, most common
- Seed Warts: Painless
- Plantar: Soles of feet
- Genital: Most common STD, tiny, flat, cauliflower branching
Poly
- dsDNA, JC/BK, asymptomatic
- PML: Destroy white matter
- BK infection: Renal transplants
Parv
- The only ssDNA
- Distemper in cats
- 5th disease: Erythema infection rash child
2. Types of Nucleic Acid in Virus
DNA Viruses
Usually double-stranded but may be single-stranded.
RNA
Usually single; may be double, may be segmented into separate RNA pieces.
ssRNA
- Genomes ready for immediate translation are positive sense RNA
- ” ” that must be converted into proper form are negative sense RNA
3. Modes of Viral Multiplication
RNA Viruses
Enveloped, segmented ssRNA
Orthomyxoviruses/Bunyavirus/Arenaviruses
Ortho
- Influenza A, B, C, A worst
- Attaches and multiplies
Influenza Glycoproteins
- Hemagglutinin (H:): Most important, binds to host cell cant get in
- Neuraminidase (N): Budding
- Both undergo changes, decrease immune response
Influenza Mutation
- Antigenic Drift: Flu B, constant mutation, spike changes AA
- Shift: Genes/RNA sub w/a Gene from another flu virus, human gets bird flu = death
Arbovirus
- St. Louis encephalitis
- W. Nile encephalitis
- Yellow Fever
- Dengue Fever
Pandora Virus
Largest genome of any virus
Viral Genome
DNA or RNA, never both!
Preformed Enzyme in Viron
- Polymerases DNA/RNA
- Replicases Copy RNA
- Reverse Transcription: Synthesis of DNA from RNA, AIDS virus
Adsorption
Binding of virus to specific molecules on the host cell.
Penetration
Genome enters the host cell – endocytosis (engulfed)
Uncoating
The viral nucleic acid is released from the capsid.
Synthesis
Viral components are produced – envelope merges w/membrane
Assembly
New viral particles are constructed.
Release
Assembled viruses are released by budding (exocytosis)/cell lysis.
DNA Viruses
Enveloped
- Poxviruses
- Herpesvirus
- Hepadnavirus
Pox
- Largest & most complex, double-stranded DNA, specific for cytoplasm of epidermal cells (postules).
- Smallpox: Inhalation/skin contact
- 2 Causes:
- Variola Major – Highly virulent
- Variola Minor – Less virulent
- Vaccine contains vaccinia virus closely related to variola.
- Humans can get monkey/cowpox.
Herpes
- HSV1: Oral, trigeminal (5th)
- HSV2: Genitals, lumbosacral spinal nerve, sacroganglia, can be spread w/no visible lesions.
- Lays dormant/latent in nerves
Varicella-Zoster (VZV)
- Respiratory droplets/contact
- Primary infection: Chickenpox
- Results in shingles
- Live weakened vaccine
Cytomegalovirus
- Giant cells, saliva, secretions
- Asymptomatic, flu-like
Epstein-Barr (EBV)
- Saliva
- Burkitt Lymphoma: B-cell malignancy in jaw
- Nasopharyngeal Carcinoma: Epithelial cells
HHV6
70% MS patients show s/s Hodgkin’s Lymphoma
HHV7
Related to above
HHV8
Kaposi Sarcoma
Polio
: enteroviral, spinalcord