viruses. introduction viruses – latin for ‘poison’ viruses – latin for ‘poison’ viruses...
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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)
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