Transcript multiplication and variation of viruses

Chapter 30
Replication and
variation of viruses
Section 1
multiplication of
viruses
Basic steps in viral multiplication cycle
 Adsorption (attachment)
 Penetration or entry
 Uncoating to release the genome
 virion component production
 Assembly (maturation)
 Release from the cell

Productive or lytic response
the Basic steps

nonproductive response or lysogeny
 no new virus is produced
 the cell survives and divides
 the viral genetic material persists indefinitely
in a latent state
 in the case of bacteriophages

Lytic or virulent viruses
can enter only into a productive relationship

temperate viruses
can establish ether a productive or a
nonproductive relationship
Basic steps in viral multiplication cycle
self -replication
adsorption/
attachment
↓
penetration
↓
uncoating
biosynthesis
↓
assembly & release
Viral growth curve Fig 29-1
Eclipse period
Latent period
Cytopathic
effect (CPE)
Adsorption or attachment
•Nonspecific adsorption
---static electricity-combination between
virus and cell
•Specific combination
---virion attachment proteins adsorb to specific
receptor on the surface of susceptible cells
Entry
(吞饮或胞饮)
naked 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)
Uncoating
---The viral nuclei acid is
released from the capsid
ADSORPTION
ADSORPTION
Requires viral attachment protein
 Cellular receptors

PENETRATION
- ENVELOPED VIRUSES

Fusion融合with plasma membrane

Entry via endosomes内含体
PENETRATION
herpesviruses, paramyxoviruses, HIV
PENETRATION
- ENVELOPED VIRUSES

Fusion with plasma membrane

Entry via endosomes
VIRUS UPTAKE BY CLATHRIN COATED PITS内陷小窝
Called :Viropexis病毒吞饮/ endocytosis / pinocytosis
PENETRATION
NON-ENVELOPED VIRUSES
entry directly
across plasma
membrane
PENETRATION
NON-ENVELOPED VIRUSES
entry directly across
plasma membrane
UNCOATING

Need to make genome available

Once uncoating occurs, enter eclipse
period

Eclipse phase lasts until first new virus
particle formed
BIOSYNTHESIS OF VIRUSES
mRNA production
genome synthesis
protein synthesis
early protein (function protein)
late protein (structural protein)
Gene expression and genome replication
Viral
(+) mRNA
biosynthetic site
DNA in the nucleus
RNA in the cytoplasm
protein in the cytoplasm
Biosynthesis of ds-DNA virus
parental ds-DNA
in nucleus
半保留复制
⑵
progeny ds-DNA
利用核内依赖DNA
的RNA多聚酶转录
early mRNA
⑴
in the cytoplasm
early protein
later mRNA
⑶
in the cytoplasm
later protein
⑴biosynthesis of early protein---依赖DNA的DNA聚合酶等
⑵replication of progeny DNA
⑶biosynthesis of late protein
Biosynthesis of ss-RNA virus
parental ㈩ss-RNA
in the cytoplasm
+RNA acts as mRNA
㈠ss-RNA(±RNA)
early protein
later protein
(复制中间型)
progeny ㈩ss-RNA
----RNA must first transcribe the complementary
plus strand
ECLIPSE PHASE P260

The period of infection in which no
infectious viruses are found inside the
cell

The original virions lose their infectivity
soon after entry
Assembly

the process of enclosing the viral
genome in a protein capsid
release
Disintegration 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
Release
Budding through
plasma membrane
(enveloped virus)
Rupture(un-enveloped virus)
Replication cycle of virus
adsorption
• progeny viruses
• produce cell
effects---damage
and lysis of cells
penetration
assembly
and release
uncoating
biosynthesis
protein and
nucleic acid
Abnormal multiplication of viral
& interference
 Abortive infection (顿挫感染,无效感染)
When a virus infects a cell (or host), but
cannot complete the full replication cycle
( not biosynthesize their components or not
assemble virions.), i.e. a non-productive
infection.
non-permissive cells
permissive cells(容纳性细胞)
Section 2
viral variation and
resistence
defective viruses

Lacks one or more functional genes
required for viral replication

Require helper activity from another
virus for some step in replication or
maturation
interference

Two viruses often leads to an inhibition
of multiplication of one of the viruses
两种病毒同时感染同一种细胞,发生一种病毒抑制另
一种病毒复制的现象称为干扰现象
 defective interfering particle (DIP)
指缺陷病毒与其完整病毒(非缺损病毒)同时感染同一细
胞时, 能干扰完整病毒的增殖, 发挥干扰作用的缺陷病毒为
缺陷干扰颗粒(DIP)
Viral resistance
耐冷不耐热
pH5.0以下或pH9.0
以上迅速灭活