VIRUSES

It’s a Small World• Virus: a microscopic particle that gets inside a cell and often destroys the cell

• Viruses are tiny• Smaller than the smallest bacteria• Change rapidly• So small and change so often that scientists don’t know exactly how many types exist

• These properties make viruses difficult to fight

Are Viruses Living?

•Like living things, viruses contain protein and genetic material

•But viruses don’t act like living things•Can’t eat, grow, or break down food•Can’t use oxygen•Cannot function on its own

• Can only reproduce inside a living cell that serves as a host

• Host: an organism from which a parasite takes food or shelter

• Virus uses host’s cell as a tiny factory, and forces host to make viruses rather than healthy new cells

Classifying Viruses• Can be grouped together by:• Their shape• Type of disease they cause

• Life cycle• Kind of genetic material they contain

• There are 4 main shapes of viruses:

Cylinders: The tobacco mosaic virusIs shaped like a cylinder and attacks

tobacco plants.

Crystals: The polio virus is shaped like the crystal shown here.

Spacecraft: One group of viruses attacks only bacteria. Many of these look almost

like spacecraft (also called Bacteriophage).

Spheres: Influenza viruses look like spheres. HIV is another virus that has

this structure.

• Every virus is made up of genetic material inside a protein coat (also known as capsid)

• The protein coat protects the genetic material and helps a virus enter a host cell

• Many viruses have protein coat that matches characteristics of their specific host

• There are 4 main shapes of viruses: crystals, spheres, cylinders, and spacecraft

Capsid: protein coat that surrounds virus

Genetic Material• Genetic material either DNA or RNA• Most RNA is made up of one strand of nucleotides, most DNA is two strands of nucleotides

• Both DNA and RNA contain info for making proteins

• Example: viruses that cause chickenpox & warts contain DNA

• Example: viruses that cause flu, HIV, and common cold contain RNA

• One strain of virus cannot infect both plants and animals

VirusVirus Affects Affects What?What?

Which organisms?Which organisms?

Tobacco mosaicTobacco mosaic PlantsPlants Tobacco, tomato, Tobacco, tomato, pepperspeppers

Potato XPotato X PlantsPlants Potatoes, tomatoes, Potatoes, tomatoes, pepperspeppers

AdenovirusAdenovirus AnimalsAnimals Humans & other Humans & other vertebratesvertebrates

HIVHIV AnimalsAnimals Humans & other Humans & other primatesprimates

BacteriophageBacteriophage BacteriaBacteria E.Coli & other E.Coli & other bacteriabacteria

Different Kinds of Viruses & their sizes

Chicken pox (Varisella zoster virus (VZV)

Flu (Influenza virus)

Rabies virus

A Destructive House Guest• One thing that viruses do that living things also do is make more of themselves

• Viruses attack living cells and turn them into virus factories

• The cycle if a virus incorporating its genes into the genes of a host

cell is called : THE LYTIC CYCLE

A Time Bomb• Some viruses don’t go straight into lytic cycle—they put genetic material in host cells, but don’t make new viruses right away

• In the lysogenic cycle, each new cells gets a copy of the virus’s genes when the host cell divides

• The genes stay inactive for a long time • When they do become active, they begin the lytic cycle and make copies of the virus

Treating a Virus• Antibiotics don’t kill viruses

• Scientists have developed antiviral medications

• Because many viral diseases do not have a cure, it is best to prevent a viral infection from happening in the first place

• Childhood vaccinations give your immune system a “head start” on fighting viruses

• Vaccinations need to be kept current

• Also a good practice to always wash your hands