1 Applied Microbiology 5 th lecture: Chapter 6. 2 Viruses.
-
date post
22-Dec-2015 -
Category
Documents
-
view
216 -
download
3
Transcript of 1 Applied Microbiology 5 th lecture: Chapter 6. 2 Viruses.
11
Applied MicrobiologyApplied Microbiology
55thth lecture: Chapter lecture: Chapter 66
22
VirusesViruses
33
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
-> Size range –-> Size range –
most <0.2 most <0.2 μμm; requires electron microscopem; requires electron microscope
-> Virion-> Virion – fully formed virus able to establish an – fully formed virus able to establish an infectioninfection
44
VirusesViruses
Form and Function of VirusesForm and Function of Viruses
55
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
CapsidsCapsids- All viruses have All viruses have capsidscapsids - protein coats that enclose - protein coats that enclose and and
protectprotect their nucleic acid. their nucleic acid.
- Each capsid is constructed from Each capsid is constructed from identical subunitsidentical subunits calledcalled
capsomerscapsomers made of protein. made of protein.
- The capsid together with the nucleic acid areThe capsid together with the nucleic acid are
nucleoscapsidnucleoscapsid..
- Some viruses have an Some viruses have an external coveringexternal covering called called envelopeenvelope; ;
those lacking an envelope are those lacking an envelope are nakednaked
66
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
Capsids - EnvelopeCapsids - Envelope
77
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
Two structural types:Two structural types:
-> -> helicalhelical - continuous helix of capsomers forming - continuous helix of capsomers forming a a
cylindrical nucleocapsidcylindrical nucleocapsid
-> -> icosahedralicosahedral - 20-sided with 12 corners - 20-sided with 12 corners- vary in the number of capsomers- vary in the number of capsomers
- Each capsomer may be made of 1 or several - Each capsomer may be made of 1 or several proteins.proteins.
- Some are enveloped.- Some are enveloped.
88
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
helicalhelical
Influenza virus
99
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
IcosahedralIcosahedral
AdenovirusHerpes simplex virus
1010
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
Viral envelopeViral envelope-> mostly -> mostly animal virusesanimal viruses
-> acquired when the virus leaves the host cell-> acquired when the virus leaves the host cell
-> exposed proteins on the outside of the envelope, called -> exposed proteins on the outside of the envelope, called
spikesspikes, essential for attachment of the virus to the host , essential for attachment of the virus to the host cellcell
1111
VirusesViruses
Function of Capsid/EnvelopeFunction of Capsid/Envelope
-> -> ProtectsProtects the nucleic acid when the virion the nucleic acid when the virion isis
outside the host celloutside the host cell
-> Helps to -> Helps to bindbind the virion the virion to a cell surfaceto a cell surface andand
assists the assists the penetration of the viral DNApenetration of the viral DNA or or
RNA into a suitable host cellRNA into a suitable host cell
1212
VirusesViruses
Viral MorphologyViral Morphology
1313
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
Complex viruses: atypical virusesComplex viruses: atypical viruses-> Poxviruses lack a typical capsid and are covered by -> Poxviruses lack a typical capsid and are covered by a a
dense layer of dense layer of lipoproteinslipoproteins..
-> Some -> Some bacteriophagesbacteriophages have a polyhedral have a polyhedral nucleocapsid nucleocapsid
along with a helical along with a helical tailtail and and attachment fibersattachment fibers..
1414
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
Nucleic AcidsNucleic Acids
Viral genomeViral genome – either DNA or RNA but never both – either DNA or RNA but never both
-> Carries -> Carries genes necessary to invade host cellgenes necessary to invade host cell and redirect and redirect
cell’s activity to cell’s activity to make new virusesmake new viruses
-> -> Number of genes is low -Number of genes is low - varies for each type of virus – varies for each type of virus – fewfew
to hundredsto hundreds
1515
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
DNA virusesDNA viruses -> usually -> usually double stranded (ds)double stranded (ds) but may be single but may be single stranded (ss)stranded (ss)-> circular or linear-> circular or linear
RNA virusesRNA viruses -> usually -> usually single strandedsingle stranded, may be , may be double double strandedstranded, , may be segmented into separate RNA piecesmay be segmented into separate RNA pieces-> ssRNA genomes ready for -> ssRNA genomes ready for immediate immediate translationtranslation are are positive-sense RNApositive-sense RNA..-> ssRNA genomes that must be -> ssRNA genomes that must be converted into converted into properproper formform are are negative-sense RNAnegative-sense RNA..
1616
VirusesViruses
General Structure of VirusesGeneral Structure of Viruses
Pre-formed enzymes may be present.Pre-formed enzymes may be present.
-> polymerases – DNA or RNA-> polymerases – DNA or RNA
-> replicases – copy DNA-> replicases – copy DNA
-> reverse transcriptase –synthesis of DNA from RNA -> reverse transcriptase –synthesis of DNA from RNA
(AIDS virus)(AIDS virus)
1717
VirusesViruses
How Viruses are classifiedHow Viruses are classified
-> Main criteria presently used are -> Main criteria presently used are structurestructure, , chemical chemical compositioncomposition, and , and genetic makeupgenetic makeup..
-> No taxa above -> No taxa above Family Family (no kingdom, phylum, etc.) (no kingdom, phylum, etc.)
-> Currently recognized: 3 orders, 63 families, and 263 -> Currently recognized: 3 orders, 63 families, and 263 genera genera of virusesof viruses
-> Family name ends in -viridae, i.e.Herpesviridae-> Family name ends in -viridae, i.e.Herpesviridae
-> Genus name ends in -virus, Simplexvirus-> Genus name ends in -virus, Simplexvirus
-> Herpes simplex virus I (HSV-I)-> Herpes simplex virus I (HSV-I)
1818
VirusesViruses
How Viruses are classifiedHow Viruses are classified
1919
VirusesViruses
How Viruses are classifiedHow Viruses are classified
2020
VirusesViruses
Modes of Viral MultiplicationModes of Viral Multiplication
General phases in General phases in animal virusanimal virus multiplication multiplication cycle:cycle:
-> -> AdsorptionAdsorption - binding of virus to specific molecule on - binding of virus to specific molecule on host host
cellcell-> -> PenetrationPenetration - genome enters host cell - genome enters host cell-> -> UncoatingUncoating – the viral nucleic acid is released from the – the viral nucleic acid is released from the
capsidcapsid-> -> SynthesisSynthesis – viral components are produced – viral components are produced-> -> AssemblyAssembly – new viral particles are constructed– new viral particles are constructed-> -> ReleaseRelease – assembled viruses are released by budding – assembled viruses are released by budding
(exocytosis) or cell lysis(exocytosis) or cell lysis
2121
VirusesVirusesModes of Viral MultiplicationModes of Viral Multiplication
2222
VirusesVirusesAdsorption and Host RangeAdsorption and Host Range
-> Virus coincidentally collides with a susceptible host -> Virus coincidentally collides with a susceptible host cellcell
and adsorbs specifically to and adsorbs specifically to receptor sitesreceptor sites on the cell on the cell
membranemembrane
-> Spectrum of cells a virus can infect – -> Spectrum of cells a virus can infect – host rangehost range -> hepatitis B – human liver cells-> hepatitis B – human liver cells
-> poliovirus – primate intestinal and nerve cells-> poliovirus – primate intestinal and nerve cells
-> rabies – various cells of many mammals-> rabies – various cells of many mammals
2323
VirusesVirusesAdsorptionAdsorption
2424
VirusesViruses
PenetrationPenetration
Flexible cell membrane is penetrated by the Flexible cell membrane is penetrated by the whole virus or its nucleic acid by:whole virus or its nucleic acid by:
-> -> endocytosisendocytosis – entire virus is engulfed and enclosed – entire virus is engulfed and enclosed in ain a
vacuole or vesiclevacuole or vesicle
-> -> fusionfusion – envelope – envelope merges directly with membranemerges directly with membrane
resulting in nucleocapsid’s entry into cytoplasmresulting in nucleocapsid’s entry into cytoplasm
2525
VirusesViruses
PenetrationPenetration
Endocytosis
Fusion
2626
VirusesViruses
Replication and Protein ProductionReplication and Protein Production
-> -> Varies Varies depending on whether the virus is a depending on whether the virus is a DNA or RNA DNA or RNA virusvirus
-> -> DNA virusesDNA viruses generally are replicated and assembled generally are replicated and assembled in in the the nucleus.nucleus.
-> -> RNA virusesRNA viruses generally are replicated and assembled generally are replicated and assembled in in the the cytoplasm.cytoplasm.
-> Positive-sense RNA contain the message for -> Positive-sense RNA contain the message for translation.translation.
-> Negative-sense RNA must be converted into positive--> Negative-sense RNA must be converted into positive-sense sense message.message.
2727
VirusesViruses
ReleaseRelease
Assembled viruses leave host cell in one of two ways:Assembled viruses leave host cell in one of two ways:
-> -> buddingbudding – exocytosis; nucleocapsid binds to membrane – exocytosis; nucleocapsid binds to membrane whichwhich pinches off and sheds the viruses gradually; cell is not pinches off and sheds the viruses gradually; cell is not immediately destroyedimmediately destroyed
-> -> lysislysis – nonenveloped and complex viruses released when – nonenveloped and complex viruses released when cellcell dies and rupturesdies and ruptures
Number of viruses released is variableNumber of viruses released is variable -> 3,000-4,000 released by poxvirus-> 3,000-4,000 released by poxvirus -> >100,000 released by poliovirus-> >100,000 released by poliovirus
2828
VirusesViruses
ReleaseRelease
Budding
Budding of HIV from T-cells
2929
VirusesViruses
Damage to Host CellsDamage to Host Cells
Cytopathic effectsCytopathic effects - virus-induced damage to cells: - virus-induced damage to cells:
1. Changes in size & shape1. Changes in size & shape
2. Cytoplasmic inclusion bodies2. Cytoplasmic inclusion bodies
3. Nuclear inclusion bodies3. Nuclear inclusion bodies
4. Cells fuse to form multinucleated cells.4. Cells fuse to form multinucleated cells.
5. Cell lysis5. Cell lysis
6. Alter DNA6. Alter DNA
7. Transform cells into cancerous cells7. Transform cells into cancerous cells
3030
VirusesViruses
Damage to Host CellsDamage to Host CellsCytopathic effectsCytopathic effects
Herpes simplex virus -> multinucleated giant cells multinucleated giant cells (skin cells)(skin cells)
Cytosolic inclusion bodies
3131
VirusesViruses
Damage to Host CellsDamage to Host Cells
3232
VirusesVirusesPersistent Infections Persistent Infections
-> -> Cells can maintain a carrier relationshipCells can maintain a carrier relationship
-> -> Persistent infectionsPersistent infections - cell harbors the virus and is not - cell harbors the virus and is not
immediately lysedimmediately lysed
-> -> Can last weeks or host’s lifetime; several can periodically Can last weeks or host’s lifetime; several can periodically
reactivate – reactivate – chronic latent statechronic latent state
- measles virus – may remain hidden in brain cells for many - measles virus – may remain hidden in brain cells for many yearsyears
- herpes simplex virus – cold sores and genital herpes- herpes simplex virus – cold sores and genital herpes
- herpes zoster virus – chickenpox and shingles- herpes zoster virus – chickenpox and shingles
3333
VirusesVirusesPersistent Infections Persistent Infections
-> -> Cells can maintain a carrier relationshipCells can maintain a carrier relationship
->-> Some animal viruses enter host cell and permanently Some animal viruses enter host cell and permanently alter alter its its
genetic materialgenetic material resulting in cancer – resulting in cancer – transformationtransformation of the of the cell.cell.
->-> Transformed cells have increased rate of growth, alterations Transformed cells have increased rate of growth, alterations inin
chromosomes, and capacity to divide for indefinite time chromosomes, and capacity to divide for indefinite time periods periods
resulting in resulting in tumorstumors..
->-> Mammalian viruses capable of initiating tumors are called Mammalian viruses capable of initiating tumors are called
oncovirusesoncoviruses..
- Papillomavirus – cervical cancer- Papillomavirus – cervical cancer
- Epstein-Barr virus – Burkitt’s lymphoma- Epstein-Barr virus – Burkitt’s lymphoma
3434
VirusesViruses
Bacteriophages Bacteriophages
->-> Bacteriophages Bacteriophages – – bacterial virusesbacterial viruses (phages) (phages)
-> Most widely studied are those that infect -> Most widely studied are those that infect Escherichia Escherichia colicoli – –
complex structure, complex structure, DNADNA
-> Multiplication goes through similar stages as animal -> Multiplication goes through similar stages as animal viruses. viruses.
-> Only the nucleic acid enters the cytoplasm - uncoating -> Only the nucleic acid enters the cytoplasm - uncoating is notis not
necessary.necessary.
-> Release is a result of -> Release is a result of cell lysiscell lysis induced by viral enzymes induced by viral enzymes and and
accumulation of viruses - accumulation of viruses - lytic cyclelytic cycle..
3535
VirusesViruses
Bacteriophages - Replication Bacteriophages - Replication
1. Adsorption1. Adsorption – binding of virus to – binding of virus to specific molecule on host cellspecific molecule on host cell
2. Penetration2. Penetration –genome enters host –genome enters host cellcell
3. Replication3. Replication – viral components – viral components producedproduced
4. Assembly - 4. Assembly - viral components viral components assembledassembled
5. Maturation5. Maturation – completion of viral – completion of viral formationformation
6. Release6. Release – viruses leave cell to infect – viruses leave cell to infect other cellsother cells
3636
VirusesViruses
Bacteriophages – Life Cycles Bacteriophages – Life Cycles
3737
VirusesVirusesBacteriophages Bacteriophages
Lysogeny: The Silent Virus InfectionLysogeny: The Silent Virus Infection
-> Not all phages complete the lytic cycle.-> Not all phages complete the lytic cycle.
-> Some DNA phages, called -> Some DNA phages, called temperate phagestemperate phages, undergo , undergo adsorptionadsorption and penetration but don’t replicate.and penetration but don’t replicate.
-> The viral genome inserts into bacterial genome and -> The viral genome inserts into bacterial genome and becomes anbecomes an inactive inactive prophageprophage - - the cell is not lysed.the cell is not lysed.
-> Prophage is retained and copied during normal cell division-> Prophage is retained and copied during normal cell division resulting in the transfer of resulting in the transfer of temperate phage genometemperate phage genome to all to all host host cell progeny – cell progeny – lysogenylysogeny..
->-> InductionInduction can occur resulting in activation of lysogenic can occur resulting in activation of lysogenic prophageprophage followed by viral replication and cell lysis.followed by viral replication and cell lysis.
3838
VirusesVirusesBacteriophages Bacteriophages
Lysogeny: The Silent Virus InfectionLysogeny: The Silent Virus Infection
-> Lysogeny results in the spread of the virus without killing -> Lysogeny results in the spread of the virus without killing the the host cell.host cell.
-> Phage genes in the bacterial chromosome can cause the -> Phage genes in the bacterial chromosome can cause the production of production of toxinstoxins or or enzymes that cause pathologyenzymes that cause pathology – – lysogeniclysogenic conversion.conversion.
- Corynebacterium diphtheriae- Corynebacterium diphtheriae - Vibrio cholerae- Vibrio cholerae - Clostridium botulinum- Clostridium botulinum
3939
VirusesViruses
Bacteriophages Bacteriophages
4040
VirusesViruses
PrionsPrions
PrionsPrions - misfolded proteins, - misfolded proteins,
contain no nucleic acidcontain no nucleic acid
-> cause transmissible spongiform -> cause transmissible spongiform encephalopathies - neurodegenerative encephalopathies - neurodegenerative diseases (fibrillation of proteins)diseases (fibrillation of proteins)
-> common in animals:-> common in animals:- scrapie in sheep & goats- scrapie in sheep & goats
- bovine spongiform encephalopathies (BSE), - bovine spongiform encephalopathies (BSE),
mad cow diseasemad cow disease
- humans – Creutzfeldt-Jakob Syndrome (CJS)- humans – Creutzfeldt-Jakob Syndrome (CJS)
!!! Extremely resistant to usual sterilization !!! Extremely resistant to usual sterilization techniques !!!techniques !!!
4141
VirusesVirusesDetection and Treatment of Animal Viral Detection and Treatment of Animal Viral
InfectionsInfections
-> More difficult than other agents-> More difficult than other agents
-> Consider overall clinical picture-> Consider overall clinical picture
-> Take appropriate sample -> Take appropriate sample - Infect cell culture- look for characteristic cytopathic effects- Infect cell culture- look for characteristic cytopathic effects
- Screen for parts of the virus- Screen for parts of the virus- Screen for immune response to virus (antibodies)Screen for immune response to virus (antibodies)
-> Antiviral drugs can cause serious side effects-> Antiviral drugs can cause serious side effects