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