Viruses

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Viruses

• The smallest life forms
• From 3-200 genes
• Obligate intracellular parasites
• Known from ancient times

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Discovery of a Virus Disease Foot and Mouth
Disease Virus 1892
Kleenex PLEASE !
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Great Britain 2001, Burning Cows
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Viruses
General Characteristics Living or Dead?
Neither Not Cells Obligate intracellular
parasites Small .. 20nm 350nm Single type
of nucleic acid Protective Coat Specific
Host Range
Streptococcus
E. coli
Yeast Cell
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Virus Structure
Capsids, Nucleic Acid, Envelope
Enveloped
Icosahedral
Helical
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Virus Structure
Icosahedral

• Capsid protein coat
• Capsomeres subunits of the
• protein coat
• Symmetry 12 Corners
• 20 Faces
• 30 Edges

Nucleic acid usually not ordered inside
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Virus Structure
Nucleic Acid Genome
Properties RNA or DNA (not both) Only viruses
among all of life can have RNA as a genome Single
stranded or double stranded Only viruses among
all of life can have single stranded genomes One
piece or multiple Linear or circular As few as 3
genes, as many as 250 genes
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The Structure of an Influenza virus
Envelope Spikes Helical nucleoprotein
Influenza has ssRNA in 8 segments (8 genes)
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Microbe of the Week

• Influenza virus causes epidemic influenza
• An enveloped segmented ssRNA virus
• There are human adapted strains but also, equine,
  swine, domestic bird (chicken) Flu strians
• In nature, Influenza is a wild bird virus
• Influenza mutates rapidly and sometimes jumps
  species

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Microbe of the Week
Influenza virus is cultivated in embryonating
chicken eggs
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Microbe of the Week
Influenza virus undergoes mutational changes each
year necessitating a new vaccine strain be
prepared Antigenic Drift Periodically a
completely new strain emerges from pigs or birds
which is pathogenic for humans. Antigenic
Shift
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The Structure of a Herpesvirus
Tegument
Spikes Envelope
Icosahedral cores
Herpesvirus has dsDNA coding for about 60 genes
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BacteriophagesViruses of bacteria
A complex bacteriophage
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Virus Multiplication
A virus must invade a host cell and direct the
host's metabolic machinery to produce viral
enzymes and structural components such as the
nucleocapsid and copies of the Genome.
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Virus Multiplication
Steps in multiplication bacteriophage Attachment
Penetration Biosysnthesis Assembly Release
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Virus Multiplication
The one-step growth curve bacteriophage
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Virus Multiplication

• Multiplication of Animal Viruses
• Animal viruses adsorb to the plasma membrane.
• Penetration occurs by endocytosis or fusion.
• Animal viruses are uncoated.
• The DNA of most DNA viruses is released into
• the nucleus of the host cell.
• Multiplication of RNA viruses occurs in the
• cytoplasm of the host cell.

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Virus Multiplication
Entry and Uncoating
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Virus Multiplication
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Virus Multiplication
HIV Virus budding
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Virus Multiplication
A () RNA Animal Virus
() means that the polarity of the ssRNA is
the same as messenger RNA
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DNA Polymerases
Cellullar DNA Polymerase(s) DNA ?
DNA Transcriptase DNA ? mRNA, tRNAS, rRNA
DNA Viruses Can use cellular polymerases or can
code for their own DNA pol and Transcriptase
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RNA and RT Polymerases
RNA Viruses RNA Polymerase. RNA dependent
RNA polymerase
Retroviruses (also RNA viruses) Reverse
Transcriptase.. .RNA dependent DNA
polymerase
These are unique polymerases in all of life and
found only with viruses
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Virus Infections
Types of Infections
Acute Persistent Recurrent Latent Oncogenic
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Virus Infections
Types of Infections Example
Acute Influenza, Rotavirus, WNV Persistent
Recurrent Latent Oncogenic
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Virus Infections
Types of Infections Example
Acute Influenza, Rotavirus, WNV Persistent
HIV, con-Rubella Recurrent Latent Oncogenic
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Virus Infections
Types of Infections Example
Acute Influenza, Rotavirus, WNV Persistent
HIV, congenital Rubella Recurrent Herpes
simplex (Cold sores) Latent Oncogenic
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Virus Infections
Types of Infections Example
Acute Influenza, Rotavirus, WNV Persistent
HIV, con-Rubella Recurrent Herpes simplex
(Cold sores) Latent Varicella Zoster
(Chickenpox) Oncogenic
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Virus Infections
Types of Infections Example
Acute Influenza, Rotavirus, WNV Persistent
HIV, con-Rubella Recurrent Herpes simplex
(Cold sores) Latent Varicella Zoster
(Chickenpox) Oncogenic Human Papilloma virus