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