VirusesViruses

What Is A VirusWhat Is A Virus

A microscopic A microscopic parasite that parasite that infects cells in infects cells in biological biological organisms.organisms.

Do Viruses LiveDo Viruses Live

Viruses are considered neither alive Viruses are considered neither alive nor deadnor dead

Viruses a Viruses a HOST Can reproduce only by invading and Can reproduce only by invading and

controlling other cells as they lack the controlling other cells as they lack the cellular machinery for self-cellular machinery for self-reproductionreproduction

Performs no cellular functions on its Performs no cellular functions on its own.own.

Viruses Are ParasitesViruses Are Parasites

Viruses are parasites, meaning Viruses are parasites, meaning they cannot survive and thrive they cannot survive and thrive without a host or group of host without a host or group of host cells.cells.

The hosts provide viruses with all The hosts provide viruses with all the chemicals and molecules they the chemicals and molecules they need to survive and reproduce. need to survive and reproduce.

Viruses are completely dependent Viruses are completely dependent upon other organisms to function.upon other organisms to function.

PhysiologyPhysiology

Consists of:Consists of: A strand of genetic A strand of genetic

materialmaterial An outer protective An outer protective

protein coat called protein coat called a a CASPID

Tail fibres that Tail fibres that allow the virus to allow the virus to anchor onto host anchor onto host cellscells

Viruses are SpecificViruses are Specific

Specific viruses infect specific Specific viruses infect specific cellscells Example: The Influenza Virus Example: The Influenza Virus

attacks the cells in the respiratory attacks the cells in the respiratory system and is responsible for flusystem and is responsible for flu

Example: Human Immunodeficiency Example: Human Immunodeficiency Virus (HIV) attacks the white blood Virus (HIV) attacks the white blood cells of the human immune systemcells of the human immune system

Virus ShapesVirus Shapes

Viruses can be classified by their Viruses can be classified by their shapeshape

Examples of virus shapes are:Examples of virus shapes are: RetrovirusRetrovirus BacteriophageBacteriophage AndeovirusAndeovirus Pox VirusPox Virus Tobacco Mosaic VirusTobacco Mosaic Virus

RetrovirusRetrovirus

HIV destroys white blood cellsHIV destroys white blood cells The loss of these cells impedes the ability of The loss of these cells impedes the ability of

the immune system to fight infectionthe immune system to fight infection AIDS occurs when the body’s immune system AIDS occurs when the body’s immune system

has collapsed and the body is open to infectionhas collapsed and the body is open to infection

BacteriophageBacteriophage

Bacteriophages Bacteriophages are bacteria are bacteria “eaters”.“eaters”.

They attack and They attack and destroy destroy bacteriabacteria

AdenovirusAdenovirus The common cold is The common cold is

caused by the caused by the RhinovirusRhinovirus

Symptoms include Symptoms include coughing, sneezing, coughing, sneezing, sore throat and a runny sore throat and a runny nosenose

No cure for the No cure for the common cold except for common cold except for rest and lost of fluidsrest and lost of fluids

Tobacco Mosaic VirusTobacco Mosaic Virus

Pox VirusPox Virus

Small PoxSmall Pox Attacks blood Attacks blood

vessels in the vessels in the skin and around skin and around the mouth and the mouth and throatthroat

Causes rashes Causes rashes and fluid filled and fluid filled blistersblisters

Ebola VirusEbola Virus

Foot and Mouth DiseaseFoot and Mouth Disease

Highly contagious, from cattle and Highly contagious, from cattle and pigspigs

SARSSARS

Severe Acute Respiratory SyndromeSevere Acute Respiratory Syndrome

ReplicationReplication

There are generally 4 steps to There are generally 4 steps to replicationreplication

1.1. Attachment and EntranceAttachment and Entrance

2.2. Synthesis of protein and Synthesis of protein and genetic materialgenetic material

3.3. Assembly of the new virusesAssembly of the new viruses

4.4. Release of new virus particlesRelease of new virus particles

ReplicationReplication

ReplicationReplication

ReplicationReplication

The process is known as the The process is known as the LYTICLYTIC CYCLECYCLE

LYSIS: LYSIS: The destruction or The destruction or bursting open of a cell.bursting open of a cell.

This leads to the releasing of This leads to the releasing of viruses from a cell.viruses from a cell.

ReplicationReplication

Can be completed in as little as 25-Can be completed in as little as 25-45 min and can reproduce hundreds 45 min and can reproduce hundreds of new viruses under ideal lab of new viruses under ideal lab conditionsconditions

Lysogenic CycleLysogenic Cycle

Viruses can lie dormant within any host Viruses can lie dormant within any host or environment until the proper or environment until the proper conditions for their activity are provided. conditions for their activity are provided.

LYSOGENY: LYSOGENY: the dormant state of a virusthe dormant state of a virus The virus’ genetic material becomes The virus’ genetic material becomes

integrated into cell and is replicated to integrated into cell and is replicated to all daughter cells until activated by a all daughter cells until activated by a stimulusstimulus

ActivationActivation

Can be caused by environmental Can be caused by environmental changes like temperature or pHchanges like temperature or pH

Can be caused by changes in Can be caused by changes in available nutrientsavailable nutrients

The above can trigger the The above can trigger the lytic lytic cyclecycle and new viruses are formed and new viruses are formed and releasedand released

Viruses As PathogensViruses As Pathogens

Viruses attack cells as they reproduce killing the host cells

The destruction of these cells causes symptoms of diseases

Antibiotics do nothing to stop viruses

VaccinesVaccines

Made from dead or weakened viral cells can stimulate the body to fight viruses