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?