VirusesViruses

A submicroscopic pathogenA submicroscopic pathogen

From the Latin: Poison: A slimy liquidFrom the Latin: Poison: A slimy liquid

VirusesViruses

NotNot usually considered to be usually considered to be a living a living organismorganism

Symptoms depend on the host cells Symptoms depend on the host cells that that they infect to reproducethey infect to reproduce Inserts its genetic material and takes over Inserts its genetic material and takes over

host’s functions to produce more viral host’s functions to produce more viral protein and genetic material instead of the protein and genetic material instead of the cell’s usual products.cell’s usual products.

VirusesViruses

Structure outside a host Structure outside a host cellcell Has an inner core of Has an inner core of

nucleic acid nucleic acid (RNA or DNA)(RNA or DNA) Protein coat surrounding Protein coat surrounding

nucleic acidnucleic acid Various sizes and shapesVarious sizes and shapes

VirusesViruses

Viruses Viruses attaches to a host cellattaches to a host cell Virus Virus injects its DNA into host cell injects its DNA into host cell

nucleusnucleus Then it can do one of two thingsThen it can do one of two things

1)Lysogenic Phase1)Lysogenic Phase RNA from virus becomes part of the DNA in RNA from virus becomes part of the DNA in

host cellhost cell No obvious change in host cell No obvious change in host cell It is in the It is in the dormant stage dormant stage until virus gets until virus gets

triggered and enters the lytic cycletriggered and enters the lytic cycle

VirusesViruses

2) Lytic Cycle2) Lytic Cycle Host cell’s DNA is destroyedHost cell’s DNA is destroyed Cell’s machinery is used to produce new Cell’s machinery is used to produce new

virusesviruses The The host cell breaks open to release the host cell breaks open to release the

new viruses, which go and infect new cellsnew viruses, which go and infect new cells

Effects of VirusesEffects of Viruses

They cause disease in all living They cause disease in all living organismsorganisms

When the virus breaks out of the host cell When the virus breaks out of the host cell is is usually destroys itusually destroys it

Electron micrograph of a cluster of Electron micrograph of a cluster of influenza virusesinfluenza viruses

VirusesViruses

This picture shows the structure of This picture shows the structure of thethe Human Immunodeficiency Human Immunodeficiency VirusVirus(HIV). (HIV).

Effect of VirusesEffect of Viruses

They cause disease in plantsThey cause disease in plants Micrograph of the virus that causes Micrograph of the virus that causes

tobacco mosaic disease tobacco mosaic disease

Effect of VirusesEffect of Viruses

They cause disease in bacteriaThey cause disease in bacteria We call them bacteriophagesWe call them bacteriophages