VIRUSESVIRUSES

INTRODUCTIONINTRODUCTION

Viruses – Latin for ‘poison’Viruses – Latin for ‘poison’ Viruses are Viruses are NOT NOT classified as living (they lack classified as living (they lack

cytoplasm, organelles and a cell membrane)cytoplasm, organelles and a cell membrane) Viruses cannot carry any metabolic functions Viruses cannot carry any metabolic functions

and cannot reproduce on its ownand cannot reproduce on its own Viruses require a living HOST cell to reproduceViruses require a living HOST cell to reproduce

PARTS OF THE VIRUSPARTS OF THE VIRUS

An inner genetic An inner genetic material (nucleic acid material (nucleic acid - DNA or RNA)- DNA or RNA)

Capsid – outer Capsid – outer protein coat protein coat (provides shape and (provides shape and accounts for 95% of accounts for 95% of the virus)the virus)

Some viruses have spikes or a mechanism to Some viruses have spikes or a mechanism to attach to host cellsattach to host cells

Scientists classify viruses Scientists classify viruses based on their unique based on their unique characteristics, including:characteristics, including:

size and shape of the capsid shape and structure of the virus type(s) of diseases the virus causes type of genetic material (RNA or DNA) method of reproduction

Virus Shape and Structure:

There are different shapes for viruses:There are different shapes for viruses:

1) Helical (Spiral) 1) Helical (Spiral) 2) Enveloped2) Enveloped 3) Phage (many sides with a tail)3) Phage (many sides with a tail)

LOOKING IN…

Viruses were first looked at under electron Viruses were first looked at under electron microscopesmicroscopes

Size Range: 20 nm to 400 nmSize Range: 20 nm to 400 nm 1 nm = 1 billionth of a metre (101 nm = 1 billionth of a metre (10-9 -9 m)m) 1 mm = 1 millionth of a metre (101 mm = 1 millionth of a metre (10-6 -6 m)m)

PICTURE THIS…You can fit almost 5000 influenza PICTURE THIS…You can fit almost 5000 influenza viruses on the head of a pinviruses on the head of a pin

VIRUS TYPESThere are many virus types There are many virus types

including:including: RetrovirusesRetroviruses ReovirusesReoviruses AdenovirusesAdenoviruses RhabdovirusesRhabdoviruses Orthomyxoviruses, etc.Orthomyxoviruses, etc.

Each has a different inner Each has a different inner nucleic acidnucleic acid, , coatcoat and and structurestructure

BACTERIOPHAGE

Special category of virus

Word means ‘bacteria- eater’ – they infect and destroy bacterial cells

Have a unique shape with a head and tail region

THE HOST

HostHost – the cell on which another organism lives – the cell on which another organism lives Host Range – Host Range – the limited # of host species, tissues or the limited # of host species, tissues or

cells a virus can infectcells a virus can infect Ex. Ex. Rabies virusRabies virus – infects rodents, dogs, humans (it – infects rodents, dogs, humans (it

has a has a broad host rangebroad host range)) Ex. Ex. Human Cold VirusHuman Cold Virus – only infects cells of the upper – only infects cells of the upper

respiratory tractrespiratory tract Ex. Ex. HIV HIV - only infects certain types of white blood - only infects certain types of white blood

cells (both have a cells (both have a narrow rangenarrow range))

Methods of Reproduction

Incubation periodIncubation period = the time it takes between = the time it takes between when the virus infects a cell and when when the virus infects a cell and when symptoms appear (when the virus ruptures the symptoms appear (when the virus ruptures the cell).cell).

There are There are twotwo types of reproduction/replication: types of reproduction/replication: The The LYTIC LYTIC cyclecycle The The LYSOGENIC LYSOGENIC cyclecycle

Lytic cycle: ATTACHMENT & ENTRYATTACHMENT & ENTRY

- The virus invades a - The virus invades a host cellhost cell and injects its genetic and injects its genetic material into the material into the host cellhost cell. . REPLICATIONREPLICATION

- The - The host cellhost cell replicates the parts of the virus (synthesis of replicates the parts of the virus (synthesis of proteins and nucleic acids).proteins and nucleic acids). ASSEMBLYASSEMBLY:: - New viruses are assembled in the - New viruses are assembled in the host cell.host cell. RELEASE:RELEASE: - The new viruses are released from the infected - The new viruses are released from the infected host cell host cell to to invade new cells invade new cells - The - The host cell host cell is is LYSED LYSED (bursts open) and dies.(bursts open) and dies.Note:Note: 25-45 min. production of 100s of viruses 25-45 min. production of 100s of viruses

LYTIC CYCLELYTIC CYCLE

LySOGENic cycle: ATTACHMENT & ENTRYATTACHMENT & ENTRY

- The virus invades a - The virus invades a host cellhost cell and injects its genetic and injects its genetic material into the material into the host cellhost cell. . PROVIRUS FORMATIONPROVIRUS FORMATION

- The viral DNA is inserted into the - The viral DNA is inserted into the host cell’shost cell’s DNA and is referred DNA and is referred to as a to as a provirus.provirus.

DORMANCYDORMANCY:: - The viral DNA remains - The viral DNA remains dormant dormant (inactive) for a period of time (inactive) for a period of time while replication of the while replication of the host cellhost cell occurs without any harm to it. occurs without any harm to it. - The viral DNA is activated and extracted from the - The viral DNA is activated and extracted from the host cell host cell by a by a “ “trigger” or “stimulus”.trigger” or “stimulus”. - This trigger stimulates the - This trigger stimulates the lytic lytic cycle to begin and the infection cycle to begin and the infection and death of the and death of the host cell.host cell.

REPLICATIONREPLICATION- The - The host cellhost cell replicates the parts of the virus (synthesis of replicates the parts of the virus (synthesis of

proteins and nucleic acids).proteins and nucleic acids). ASSEMBLYASSEMBLY:: - New viruses are assembled in the - New viruses are assembled in the host cell.host cell. RELEASE:RELEASE: - The new viruses are released from the infected - The new viruses are released from the infected host cell host cell to to invade new cells invade new cells - The - The host cell host cell is is LYSED LYSED (bursts open) and dies.(bursts open) and dies.

LYTIC/LYSOGENIC CYCLELYTIC/LYSOGENIC CYCLE

HUMANS AND VIRUSES

Many common human diseases are caused by Many common human diseases are caused by virusesviruses

Viruses attack cells as it reproducesViruses attack cells as it reproduces The destruction of the cells causes the The destruction of the cells causes the

symptoms of diseasesymptoms of disease

VIRUSES AND CANCERVIRUSES AND CANCER Some viruses can cause cancer by Some viruses can cause cancer by

adding specific genes to an infected adding specific genes to an infected cell transforming it into a cancer cellcell transforming it into a cancer cell

VirusVirus Cancer TypeCancer Type

Human Human papillomaviruspapillomavirus

Cervical, skin, etc.Cervical, skin, etc.

Hepatitis B/CHepatitis B/C Liver cancer, lymphomasLiver cancer, lymphomas

Epstein-Barr virusEpstein-Barr virus Burkitt’s lymphoma, Burkitt’s lymphoma, Hodgkin’s lymphomaHodgkin’s lymphoma

ANTIBIOTICS and ANTIBIOTICS and VACCINESVACCINES

Antibiotics Antibiotics - substances inhibiting the growth of substances inhibiting the growth of

some microorganisms some microorganisms - They destroy bacteria They destroy bacteria NOTNOT viruses viruses VaccinesVaccines

- Liquid preparations of dead or - Liquid preparations of dead or weakened viral/bacterial cells that weakened viral/bacterial cells that stimulate the body’s stimulate the body’s immune system immune system to fight and produce to fight and produce antibodies antibodies

INFLUENZA VIRUSINFLUENZA VIRUS Physical/chemical Physical/chemical

differences result in flu differences result in flu types A,B,Ctypes A,B,C

Strains described by Strains described by protein coat, isolation protein coat, isolation year and locationyear and location

Destroys cells in upper Destroys cells in upper respiratory tract so there respiratory tract so there is no sweeping of foreign is no sweeping of foreign particlesparticles

Symptoms – sore throat, Symptoms – sore throat, congested lungscongested lungs

Human Human Immunodeficiency Immunodeficiency

Virus (HIV)Virus (HIV) Virus that causes AIDS Virus that causes AIDS

(Aquired Immunodeficiency (Aquired Immunodeficiency Syndrome)Syndrome)

Retrovirus is transmitted Retrovirus is transmitted through variety of bodily through variety of bodily fluids: blood, semen, vaginal fluids: blood, semen, vaginal fluid, breast milkfluid, breast milk

HIV attacks the immune HIV attacks the immune systemsystem

Since 1981, almost 25 Since 1981, almost 25 million people have died million people have died from AIDSfrom AIDS

Other Viral DiseasesOther Viral Diseases

Varicella zoster virus: chickenpox (children) and shingles (adults)

Variola major virus: smallpox

Poliovirus - Polio

SARS coronovirus: Severe Acute Respiratory Syndrome (SARS)