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Chapter 30
Replication and variation of
viruses
Section 1Section 1
multiplication multiplication of virusesof viruses
Basic steps in viral multiplication cycle
Adsorption (attachment)Adsorption (attachment) Penetration or entryPenetration or entry Uncoating to release the genomeUncoating to release the genome virion component productionvirion component production Assembly (maturation)Assembly (maturation) Release from the cellRelease from the cell
Productive or lytic responseProductive or lytic response
the the Basic steps
nonproductive response response or lysogeny no new virus is producedno new virus is produced the cell survives and dividesthe cell survives and divides the viral genetic material persists indefinitely ithe viral genetic material persists indefinitely i
n a latent staten a latent state in the case of bacteriophagesin the case of bacteriophages
Lytic or virulent virusesLytic or virulent viruses
can enter only into a productive relationshipcan enter only into a productive relationship
temperate virusestemperate viruses
can establish ether a productive or a nonprcan establish ether a productive or a nonproductive relationshipoductive relationship
Basic steps in viral multiplication cycle
adsorption/adsorption/attachmentattachment ↓ ↓penetrationpenetration ↓ ↓ uncoating uncoating
biosynthesisbiosynthesis ↓ ↓ assembly & releaseassembly & release
self -replication
Viral growth curve Fig 29-1
Eclipse periodEclipse period
Latent periodLatent period
Cytopathic effeCytopathic effect (CPE)ct (CPE)
Adsorption or Adsorption or attachmentattachmentAdsorption or Adsorption or attachmentattachment
••Nonspecific adsorption Nonspecific adsorption
••Specific combination Specific combination
---virion attachment proteins adsorb to specific receptor on the surface of susceptible cells
---static electricity-combination between ---static electricity-combination between virus and cellvirus and cell
UncoatingUncoatingUncoatingUncoating---The viral nuclei acid is ---The viral nuclei acid is released from the capsidreleased from the capsid
EntryEntrynaked virus---by endocytosis or viropexis
enveloped virus---by fusion of viral envelope with host-cell membrane
( 病毒胞膜与宿主细胞膜融合 )
( 吞饮或胞饮 )
ADSORPTIONADSORPTION
ADSORPTIONADSORPTION
Requires viral attachment protein Cellular receptors
PENETRATION PENETRATION - ENVELOPED VIRUSES- ENVELOPED VIRUSES
FusionFusion融合 with plasma membranewith plasma membrane
Entry via endosomesEntry via endosomes内含体
PENETRATION
herpesviruses, paramyxoviruses, HIVherpesviruses, paramyxoviruses, HIV
PENETRATION PENETRATION - ENVELOPED VIRUSES- ENVELOPED VIRUSES
Fusion with plasma membraneFusion with plasma membrane
Entry via endosomesEntry via endosomes
VIRUS UPTAKE BY CLATHRIN COATED PITS内陷小窝
Called :ViropexisCalled :Viropexis病毒吞饮 / endocytosis / pinocytosis/ endocytosis / pinocytosis
PENETRATIONNON-ENVELOPED VIRUSES
entry directly entry directly across plasma across plasma membranemembrane
PENETRATIONNON-ENVELOPED VIRUSES
entry directly across entry directly across plasma membraneplasma membrane
UNCOATING
Need to make genome availableNeed to make genome available
Once uncoating occurs, enter Once uncoating occurs, enter eclipse perieclipse periodod
Eclipse phase lasts until first new virus paEclipse phase lasts until first new virus particle formedrticle formed
BIOSYNTHESIS OF VIRUSES
mRNA productionmRNA production
genome synthesisgenome synthesis protein synthesisprotein synthesis
early protein (function protein)early protein (function protein)late protein (structural protein)late protein (structural protein)
Gene expression and genome replication
ViralViral(+) mRNA(+) mRNA
biosynthetic site
DNA in the nucleus
RNA in the cytoplasm
protein in the cytoplasm
Biosynthesis of ds-DNA virusBiosynthesis of ds-DNA virus
parental ds-DNAparental ds-DNA early mRNAearly mRNA
early proteinearly proteinin the cytoplasmin the cytoplasm
progeny ds-DNA
in nucleus
later mRNA
later protein
in the cytoplasm
半保留复制
利用核内依赖利用核内依赖 DNA DNA 的的 RNARNA 多聚酶转多聚酶转录录
⑴⑴biosynthesis of early protein---biosynthesis of early protein--- 依赖依赖 DNADNA 的的 DNADNA 聚合酶聚合酶等等⑵replication of progeny DNA
⑶biosynthesis of late protein
⑴⑴⑵
⑶
DNADNA 聚合酶聚合酶
Biosynthesis of ss-RNA virusBiosynthesis of ss-RNA virusparental parental ㈩㈩ ss-RNAss-RNA
early proteinearly proteinin the cytoplasmin the cytoplasm
acts directly as mRNAacts directly as mRNA
㈠㈠ ss-RNA(±RNA)ss-RNA(±RNA) later protein
progenyprogeny ㈩㈩ ss-RNAss-RNA
(( 复制中间型复制中间型 ))
-----RNA must first transcribe the complementary ---RNA must first transcribe the complementary plus strandplus strand
(( 依赖依赖 RNARNA 的的 RNARNA 聚合酶聚合酶 ))
+RNA acts as mRNA+RNA acts as mRNA
ECLIPSE PHASE ECLIPSE PHASE P260P260
The period of infection in which no infectThe period of infection in which no infectious viruses are found inside the cell ious viruses are found inside the cell
The original virions lose their infectivity sThe original virions lose their infectivity soon after entryoon after entry
Assembly Assembly
the process of enclosing the viral genomthe process of enclosing the viral genome in a protein capsid e in a protein capsid
releaserelease
Disintegration 崩解崩解 : naked virus cause the host cell lysis
Budding: enveloped viruses
Budding viruses do not necessarily kill the cell. Thus, some budding viruses may be able to set up persistence
ReleaseBudding through Budding through
plasma membrane plasma membrane (enveloped virus)(enveloped virus)
Rupture(un-enveloped virus)Rupture(un-enveloped virus)
Replication cycle of virusReplication cycle of virus
adsorption adsorption
biosynthesisbiosynthesis
assembly and release
uncoatinguncoating
protein and protein and nucleic acidnucleic acid
penetrationpenetration
• progeny viruses • produce cell effects---damage and lysis of cells
Abnormal multiplication of Abnormal multiplication of viral viral & i& interferencenterference
Abortive infection ( 顿挫感染 , 无效感染无效感染 )
non-permissive cells permissive cells( 容纳性细胞 )
When a virus infects a cell (or host), but canWhen a virus infects a cell (or host), but cannot complete the full replication cycle ( not not complete the full replication cycle ( not biosynthesize their components or not assebiosynthesize their components or not assemble virions.), i.e. a non-productive infectiomble virions.), i.e. a non-productive infection. n.
Section 2Section 2
viral variation and resiviral variation and resistencestence
defective virusesdefective viruses Lacks one or more functional genes Lacks one or more functional genes
required for viral replicationrequired for viral replication
Require helper activity from another Require helper activity from another virus for some step in replication or virus for some step in replication or maturationmaturation
interferenceinterference
Two viruses often leads to an inhibition Two viruses often leads to an inhibition of multiplication of one of the virusesof multiplication of one of the viruses
两种病毒同时感染同一种细胞两种病毒同时感染同一种细胞 ,, 发生一种病毒抑制另一发生一种病毒抑制另一种病毒复制的现象称为干扰现象种病毒复制的现象称为干扰现象
指缺陷病毒与其完整病毒指缺陷病毒与其完整病毒 (( 非缺损病毒非缺损病毒 )) 同时感染同一同时感染同一细胞时细胞时 , , 能干扰完整病毒的增殖能干扰完整病毒的增殖 , , 发挥干扰作用的缺陷病发挥干扰作用的缺陷病毒为缺陷干扰颗粒毒为缺陷干扰颗粒 (DIP)(DIP)
defective interfering particle (DIP)defective interfering particle (DIP)
紫外线、 χ 线和射线可灭活
耐抗生素和甘油
消毒剂可灭活 ;包膜病毒对脂溶剂敏感
耐冷不耐热
pH5.0 以下或 pH9.0 以上迅速灭活
Viral resistanceViral resistance