Viruses, viroids, & prions
Virus Features• Obligate intracellular
parasites• Lack ribosomes and
metabolic enzymes • Small DNA or RNA genomes
in protein capsid• Do NOT respond to
antibiotics• Many do have unique
enzymes - targets for anti-viral drugs.
HostsTMV Bacteria
Influenza HIV in LeukocyteII
Viral Shapes
EnvelopesSome viruses wrap self in host membranesNot hardy outside body - need fluid for passageExample - Hepatitis A: no envelope, food/waterExample - Hepatitis B: envelope, blood/STD
Enveloped
Virus Classification and TermsKind of genetic material - DNA or RNASize and shape of capsidIs there a stolen cell membrane - envelope?Host range - organism/cell it infects and disease
- Bacteriophage - viruses that infect bacteria- Oncogenic viruses - cause cancer- Retroviruses - RNA to DNA, lysogenic
Classification
Classification
Types of Viruses
• DS DNA – Herpes virus
• SS RNA (+ strand)–Poliovirus
• SS RNA (- strand) –Influenza
• SS RNA DNA --retrovirus
Viral Replication
Lytic viral diseases are acute, rapid
Growth curve
Lysogeny
Animal Viruses
Penetration of animal viruses
• A = polio, dengue fever
• B = measles, mumps
• C = Adenovirus, Herpes
Synthesis strategies of animal viruses
Release
Latency of animal viruses
Examples – Herpesvirus, chickenpoxAttachment and penetration - same as beforeSome animal viruses are latent outside the cellLysogeny – maintenance of viral genome in cellUsually expressed at low levels for a long time,
never induced
Viroids
• Viroids are small, circular pieces of RNA that infect plants.
• Lack capsid
Prions
• Stanley Prrusiner 1982• Discovered
Proteinaceousinfective particle
• Single Protein, PrP• Disease causing• Folded differently• Prions induce change
in shape
BSE and CJD