Viral StructureViral Structure

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VirusVirusDerived from the Latin word meaning toxin or poisonDerived from the Latin word meaning toxin or poison

Is it a molecule or a microbe?

Outside of the living cell, a virus is a lifeless chemical, and seems to carry out no life function of its own. However, once it invades a living cell, the virus displays an important trait that it shares will all living things…. It reproduces!

Viruses occupy a position betweenViruses occupy a position between non-living and living matter

Types of VirusesTypes of Viruses

Viruses are grouped into 3 types according Viruses are grouped into 3 types according to to the cell type that they attackthe cell type that they attack. .

Individual viruses will only attack a certain type of cell. Individual viruses will only attack a certain type of cell.

This is called This is called host specificityhost specificity..

Type #1 – Animal VirusesType #1 – Animal Viruses

Type #2 – Plant VirusesType #2 – Plant Viruses

Type #3 – Bacterial VirusesType #3 – Bacterial Viruses

Animal VirusesAnimal Viruses

Animal Viruses attack Animal Viruses attack only animal cellsonly animal cells

The chicken pox virus The chicken pox virus ((varicella zostervaricella zoster) is a ) is a highly contagious animal highly contagious animal virus that is characterized virus that is characterized by the spots it causes all by the spots it causes all over the body.over the body. varicella zoster virusvaricella zoster virus

Plant VirusesPlant Viruses

Plant Viruses attack Plant Viruses attack

only plant cellsonly plant cells

Tobacco Mosaic VirusTobacco Mosaic Virus

(TMV) was the first virus to (TMV) was the first virus to

be discovered. be discovered.

It is an It is an RNARNA virus that affects virus that affects tobacco plantstobacco plants and other and other plants in the same family. It causes plants in the same family. It causes mottling and mottling and discolorationdiscoloration on the leaves. on the leaves.

Tobacco Mosaic VirusTobacco Mosaic Virus

Bacterial VirusesBacterial Viruses

Bacterial Viruses attack Bacterial Viruses attack

only bacterial cellsonly bacterial cells

T4 BacteriophageT4 Bacteriophage infects only infects only

E.Coli bacteriaE.Coli bacteria and is one of and is one of

the the largest bacterial viruseslargest bacterial viruses. .

T4 bacteriophage has a very distinct shape with a T4 bacteriophage has a very distinct shape with a head,head, tail and tail fibrestail and tail fibres that help to anchor it onto a bacterial that help to anchor it onto a bacterial cell.cell.

T4 BacteriophageT4 Bacteriophage

General Structures of VirusesGeneral Structures of Viruses

Helical (rod)

DNA/RNA is found coiled within the hollow tube of the rod

Can be short and rigid to long and flexible

Spherical / Icosohedral

DNA/RNA is found coiled within the center icosahedron

Complex

Attack only bacterial cells. DNA/RNA is found within the head

Unusual morphology that possess many structures

General Structure of a BacteriophageGeneral Structure of a Bacteriophage

Capsid protein

Collar

Sheath

Base Plate

Spike Tail Fibres

Bacteriophage

All viruses contain both a PROTEIN COAT (CAPSID PROTEIN) and either DNA or RNA

Defining Characteristics of All VirusesDefining Characteristics of All Viruses

Non-cellularNon-cellular Do not respire (breathe)Do not respire (breathe) Do not respond to stimuliDo not respond to stimuli Do not growDo not grow Only reproduce once they are inside other living Only reproduce once they are inside other living

organisms or cells (parasitic)organisms or cells (parasitic) Contain DNA or RNA or bothContain DNA or RNA or both Contain a protein coat around the DNA or RNAContain a protein coat around the DNA or RNA Can be stored inert (with reproducing) for long Can be stored inert (with reproducing) for long

periods of time periods of time

How are Viruses spread?How are Viruses spread?

Viruses can be spread in Viruses can be spread in many different methods:many different methods:

• Via Via water dropletswater droplets (tears, mucus) (ex. Cold, (tears, mucus) (ex. Cold, flu)flu)

• Via Via insectsinsects ( ex. Polio, ( ex. Polio, hepatitis, TMV)hepatitis, TMV)

• Via Via direct blood contactdirect blood contact, , other to child or person other to child or person to person (ex. HIV, to person (ex. HIV, Herpes)Herpes)

Cool Virus FactsCool Virus Facts Viruses range in size from Viruses range in size from

about 20 to 400 about 20 to 400 nanometers in diameter. nanometers in diameter. In perspective, a medium In perspective, a medium sized virus next to a flea is sized virus next to a flea is roughly the same as a roughly the same as a human next to a mountain human next to a mountain twice the size of Mount twice the size of Mount EverestEverest

The study of viruses is The study of viruses is known as virology and the known as virology and the scientists who study scientists who study viruses are known as viruses are known as virologistsvirologists

Above: T4 Bacteriophages attacking a bacterial cell

A few well known Viruses that can affect Humans….A few well known Viruses that can affect Humans….

Above: The influenza virus responsible for the Spanish flu that killed over 40

million people in 1918.

Below: Human Pappiloma Virus (HPV)

Above: The Ebola Virus

Below: The Noravirus responsible for causing Norwalk epidemics in hospitals

and cruise ships

Viral ReplicationViral Replication

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A closer look at the Bacteriophage life cycle…A closer look at the Bacteriophage life cycle…

Bacteria with a single ring of genetic material (in dark blue)

Bacteriophage (phage) with genetic material inside head

Step 1: Attachment

The tail fibres and base plate of the phage attach to specific surface receptors on the bacteria.

Note: Each type of phage is attracted to a certain type of surface receptor (ex. T4 bacteriophage is only attracted to receptors on E.coli cells.)

Step 2: Penetration / Entrance

The phage genetic material is injected into the bacterial cell. (Genetic material travels out of the head of the virus and through the tail into the bacterial cell.) The phage then disintegrates.

Step 1

Step 2

Phage genetic material (viral DNA or RNA)

Step 3: Replication

At this stage the viral genetic material will either integrate itself into the host DNA and enter the lysogenic pathway before it begins to replicate or it will begin to replicate within the bacterial cell.

Step 1

Step 2

Step 3

A mix of the host bacterial DNA as well as the viral genetic material (DNA or RNA)

The Lysogenic PathwayThe Lysogenic Pathway

This is a stage in which the viral DNA is basically lying dormant in the genetic material of the bacterial cell and replicating normally through binary fission along with the bacterium. This stage can last from minutes to years depending on the virus type.

Step 1

Step 2

Lysogenic Pathway

Step 4: AssemblyThe individual units of the phage are synthesized from the viral genetic material and brought together to form new phage particles.

Step 1

Step 2

Lysogenic Pathway

Step 4 Step 3

Step 5: Release of newly formed viruses The bacterial cell lyses (dies and the cell wall/membrane breaks open) and the new virus particles are released to go out and infect other bacterial cells.

Step 1

Step 2

Lysogenic Pathway

Step 4 Step 3

Step 5

Steps 1 through 5 are termed the Lytic PathwaySteps 1 through 5 are termed the Lytic Pathway

Step 1

Step 2

Lysogenic Pathway

Step 4 Step 3

Step 5

Lytic Pathway

A Electron Micrograph of bacteriophages attached to a bacterial cell wall.

Human Leukemia cells infected by the Epstein Barr Virus

Viruses and DiseaseViruses and Disease

Many human diseases are caused Many human diseases are caused by viruses including the by viruses including the common cold, the flu, common cold, the flu, chickenpox and cold sores. chickenpox and cold sores. Viruses are also the cause of Viruses are also the cause of more serious diseases such as more serious diseases such as Ebola, AIDS and SARS as well Ebola, AIDS and SARS as well as some types of cancer.as some types of cancer.

Some types of viruses like HIV Some types of viruses like HIV and herpes simplex can lay and herpes simplex can lay dormant for years whereas dormant for years whereas others begin to cause cell death others begin to cause cell death immediately until the point immediately until the point where the organism will start to where the organism will start to suffer. (you get sick!)suffer. (you get sick!)

The human body’s basic lines of defense The human body’s basic lines of defense against viruses include…against viruses include…

Primary lines of defensePrimary lines of defense1.1. SkinSkin

2.2. Mucous MembranesMucous Membranes

3.3. CiliaCilia

4.4. Stomach acidsStomach acids

5.5. Tears Tears (contain lysosomes that can destroy (contain lysosomes that can destroy virus particles)virus particles)

How would each of the above help to protect How would each of the above help to protect the body from viral infections?the body from viral infections?

Phagocytic white blood cellsPhagocytic white blood cells

Phagocytes leave the blood vessels, search out the viruses and engulf them.

Secondary Lines of Defense

White Blood Cells can also make antibodies White Blood Cells can also make antibodies against virusesagainst viruses

Antibodies attacking a virusAntibodies attacking a virus

Treatment and preventionTreatment and prevention

Anti-viral drugsAnti-viral drugs are available are available to treat the to treat the symptomssymptoms of of some viral diseases. They some viral diseases. They are not able to are not able to rid the body rid the body of the virus, only treat the of the virus, only treat the symptomssymptoms and possible slow and possible slow the replication of the virus.the replication of the virus.

The best treatment is The best treatment is prevention in the form of prevention in the form of vaccinesvaccines..

How vaccines workHow vaccines work

1.1. To produce a vaccine the virus To produce a vaccine the virus must must first be isolatedfirst be isolated

2.2. The virus is The virus is matured and allowed matured and allowed to reproduceto reproduce under very carefully under very carefully controlled conditionscontrolled conditions

3.3. The virus is The virus is chemically chemically weakenedweakened so that it is no longer so that it is no longer able to cause infection but the able to cause infection but the actual actual structure of the virusstructure of the virus is still is still completely completely intactintact. .

4.4. The weakened virus is The weakened virus is injected injected into the organisminto the organism to build up to build up aantibodiesntibodies to the specific virus. to the specific virus.