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Part III VirologyPart III Virology
A-prof. Yang Haibo A-prof. Yang Haibo Dept. of medical Microbiology and Dept. of medical Microbiology and
immunologyimmunology
virusvirus
• The smallest infectious agents The smallest infectious agents
• Contain only one kind of nucleic acidContain only one kind of nucleic acid
• Non-Non-cellural typecellural type
• Replicate only in living Replicate only in living and susceptible cellscells
Section 1 Section 1 size and size and shape of shape of virusesviruses
Size of virusesSize of viruses
• Measuring unit: nanometer, nmMeasuring unit: nanometer, nm• A small virus has a diameter of abouA small virus has a diameter of abou
t 20nm. Parvovirus t 20nm. Parvovirus 细小病毒组细小病毒组• A large virus have a diameter of up tA large virus have a diameter of up t
o 400nm. Poxviruses o 400nm. Poxviruses 痘病毒类痘病毒类
300×250nm
葡萄球菌
烟草花叶病毒
立克次体 450nm
衣原体390nm
15×300nm65×95nm
70nm
腺病毒
30nm
脊灰病毒 40nm
乙脑病毒
100nm
流感病毒10nm
卵白蛋白
噬菌体
1000nm
痘苗病毒
Size and Shape of VirusesSize and Shape of Viruses
Shapes of virusesShapes of viruses
• SphericalSpherical
• Rod-shapedRod-shaped
• Brick-shapedBrick-shaped
• Tadpole-shapedTadpole-shaped
• Bullet-shapedBullet-shaped
• FilamentFilament
White, DO and Fenner, FJ. Medical Virology, 4th Ed. 1994
Shapes of Viruses:Spherical
Shapes of Viruses :Rod-shaped
Shapes of Viruses :Brick-shaped .
Tadpole-shaped
Shapes of Viruses :Bullet-shaped
Shapes of Viruses :Filament
Section 2Section 2
structure and structure and function of function of virusesviruses
Terms and definitions in Terms and definitions in virologyvirology
virion:virion: the complete virus particle the complete virus particle
capsid:capsid: the protein shell, or coat, that e the protein shell, or coat, that encloses the nucleic acid genomencloses the nucleic acid genome
envelope:envelope: a lipid-containing membrane a lipid-containing membrane that surrounds some virus particlesthat surrounds some virus particles
Virion
Capsid
Viral core
envelope
Structure of virionStructure of virion
nucleic acid
peplomer(spike)
capsid
nucleocapsidnucleocapsid
capsomere
(Naked virus)(Naked virus)
envelopeenvelope
viral core
En
veloped
virus
En
veloped
virus
• Capsomeres:Capsomeres: morphologic units, cluster morphologic units, clusters of polypeptedess of polypeptedes
• Nucleocapsid:Nucleocapsid: the protein-nucleic acid c the protein-nucleic acid complexomplex
• Naked virusNaked virus
• Enveloped virusEnveloped virus
Terms and definitions in Terms and definitions in virologyvirology
1. Viral protein1. Viral protein
• Protect the viral genomeProtect the viral genome
• Attach to susceptible cellAttach to susceptible cell
• Structural symmetry of the virusStructural symmetry of the virus
• AntigenicAntigenic
• Enzymes (non-structral proteins) Enzymes (non-structral proteins)
2. Viral nucleic acid2. Viral nucleic acid
• In the center of the virion, Control thIn the center of the virion, Control the viral heredity and variation, respone viral heredity and variation, responsible for the infectivity.sible for the infectivity.
• The genome of a virus can be either DNA or RNA
3. Viral lipid 3. Viral lipid envelopesenvelopes
• A lipid-containing membrane that surA lipid-containing membrane that surrounds some viral particles.rounds some viral particles.
• acquired while the viral nucleocapsid acquired while the viral nucleocapsid buds through a cellular membrane in buds through a cellular membrane in the course of maturationthe course of maturation
ReleaseBudding through Budding through
plasma membrane plasma membrane (enveloped virus)(enveloped virus) Rupture(un-enveloped Rupture(un-enveloped
virus)virus)
• Viruses-encoded glycoproteins are expoViruses-encoded glycoproteins are exposed on the surface of the envelope.sed on the surface of the envelope.
• Not all viruses have the envelope, and virNot all viruses have the envelope, and viruses can be divided into 2 kinds: envelouses can be divided into 2 kinds: enveloped virus and naked virus. ped virus and naked virus.
3. Vidral lipid envelopes3. Vidral lipid envelopes
4. Viral glycoproteins4. Viral glycoproteins
• virus-encodedvirus-encoded
• Interact with a cellular receptorInteract with a cellular receptor
• Important viral antigensImportant viral antigens
Section 3Section 3 structure of viral structure of viral capsidcapsid
symmetrysymmetry
• Cubic (Icosahedral Cubic (Icosahedral 二十面体的二十面体的 ))• HelicalHelical• ComplexComplex
Icosahedral Helical
Cubic symmetryCubic symmetry
• Be of the icosahedral pattern Be of the icosahedral pattern
• Has 20 faces, each an equilateral trianHas 20 faces, each an equilateral trianglegle
• 12 vertices 12 vertices 顶角顶角• The physical appearance of the particlThe physical appearance of the particl
e is spherical e is spherical
Icosahedral symmetry
http://www.tulane.edu/~dmsander/WWW/Video/Video.html
• 20 faces20 faces• 12 vertices12 vertices
Icosahedral symmetry
Helical symmetryHelical symmetry
• Protein subunits are bound in a periProtein subunits are bound in a periodic odic 循环的 循环的 way to the viral nucleic away to the viral nucleic acid, winding it into a helixcid, winding it into a helix
Tobacco mosaic virus
adapted from:
Klug and Caspar Adv. Virus Res. 7:225
Helical symmetry
• Length controlled by nucleic Length controlled by nucleic acidacid
• Helix may be stiff or flexibleHelix may be stiff or flexible• All animal viruses with helical All animal viruses with helical
symmetry are envelopedsymmetry are enveloped
Complex symmetryComplex symmetry
• Do not exhibit simple cubic or Do not exhibit simple cubic or helical symmetry helical symmetry
• More complicated in structureMore complicated in structure
Complex symmetry
Poxvirus family
Atypical viruslike Atypical viruslike antigensantigens
Defective virusDefective virus 缺陷病毒缺陷病毒 P246P246
• A virus particle that is functionally A virus particle that is functionally deficient in some aspect of replicationdeficient in some aspect of replication
• • A virus consisted of Viral nucleic acid A virus consisted of Viral nucleic acid
and protein but cannot replicate and protein but cannot replicate without a “helper” virus that provides without a “helper” virus that provides missing function.missing function.
Viroids Viroids 类病毒类病毒
• Small infectious agents that cause diseases of plants
• Consist a single molecule of circular RNA without protein coat or envelope
prionsprions
• Infection particles composed solely Infection particles composed solely of protein with no detectable nucleiof protein with no detectable nucleic acidc acid
• Highly resistant to inactivation by hHighly resistant to inactivation by heat, formaldehayde and UVeat, formaldehayde and UV
PrionsPrions (protinaceous infection particle)
prion protein,PrP
Cellular PrP,
Scrapie prion protein
The agent of TSEs---transmissible spongiform encepha
lopathy.
Prion disease
• CNSCNS• Long incubationLong incubation• Slow course of disease Slow course of disease • Spongiform encephalopathySpongiform encephalopathy• Vacuolation Vacuolation 空泡形成 空泡形成 of neuronsof neurons• Rare in manRare in man
Clinical findings :
scrapie of sheep and goatscrapie of sheep and goat
The first TSEs, 300 years ago, EUThe first TSEs, 300 years ago, EU
bovine spongiform encephalopaty,BSEbovine spongiform encephalopaty,BSE
Kuru diseaseKuru diseaseCreutzfeld-Jakob diaseae,Creutzfeld-Jakob diaseae,CJDCJDvariant variant CJD, v-CJDCJD, v-CJD
Review questions
1.1. What are the two types of symmertry of virWhat are the two types of symmertry of viral capsid?al capsid?
2.2. What are the functions of viral proteins?What are the functions of viral proteins?3.3. What is the composition of the viral enveloWhat is the composition of the viral envelo
pe, and how is it formed?pe, and how is it formed?4.4. Which proteins of virus induce protective aWhich proteins of virus induce protective a
ntibody?ntibody?5.5. What are the differences between viruses aWhat are the differences between viruses a
nd prions?nd prions?