General Characteristics of Viruses

• small size (nm)
• acellular/noncellular
• single type of nucleic acid (DNA or RNA)
• protein coat
• obligate intracellular parasites

Viral Structure

- virion: fully developed virus particle, infections

- nucleic acid

* DNA or RNA

* single-stranded or double stranded (ssDNA, dsDNA, ssRNA, dsRNA)

* linear, circular & segmented

Viral Structure: Capsid

• protein nucleic acid
• made of capsomeres
• may have spikes

Viral Structure: Enzymes

- use host cell machinery

* drugs that interfere with viral reproduction also disrupt host cell function

- some package their own (viral) enzymes

* we can target these with drugs

Viral Structure: Envelope

- naked non-envelope

- enveloped viruses

* phospholipid membrane around capsid

* from host plasma or nuclear membrane

* must stay moist during spread from host to host

Viral Structure: Envelope

- viral & host specific proteins/carbs

* adsorption/attachment sites (bind host receptor)

~ naked viruses

~ enveloped viruses

* determine host range

* example: influenza & HIV

Attachment

Hemagglutination

Antigenic Drift

• only RNA viruses can go through this

Classification

• nucleic acid
• size & shape
• +/- envelope
• strategy for replication

Virus Taxonomy

• 6 orders -virales
• 87 families -viridae
• 19 subfamilies -
• 248 genera -virus

Growth of Viruses

Virus Plaques

Viral Multiplication

Lytic Cycle

Comparison of Bacterial & Animal Virus Replication

Virus Entry

Animal Viral Biosynthesis: DNA Genomes

Animal Viral Biosynthesis: RNA Genomes

Release By Budding or Lysis

Influenza Virus

Antigenic Shift

Retrovirus: HIV Virion Structure

HIV Lifecycle

HIV Activation

Inhibition of HIV