8、病毒的复制

2. Abortive infection
--- The virus enters the non-permissive cell which can not provid the essential enzymes & energy to viral multiplication
--- permissive cell and non-permissive cell
Non reversable Cells without the appropriate receptors are
not susceptible to the virus.
II Penetration and uncoating
Often occur simultaneously
1. Penetration
Classification of Viruses
I Classification of viruses ---basis of classification
Virion morphology Physicochemical properties of the virion Virus genome properties Virus protein proteries Genome organization and replication Antigenic properties Biologic properties
Virions are either engulfed into vacuoles by “endocytosis” or the virus envelope fuses with the plasma membrane to facilitate entry
Fusing
Some enveloped viruses fuse directly with the plasma membrane. Thus, the internal components of the virion are immediately delivered to the cytoplasm of the cell.
Replication of Viruses
As obligate intracellular parasites, Virus must enter and replicate in living cells in order to “reproduce” themselves.
This “growth cycle” involves specific attachment of virus, penetration and uncoating, nucleic acid transcription, protein synthesis, maturation and assembly of the virions and their subsequent release from the cell by budding or lysis
Uncoating is usually achieved by cellular proteases “opening up” the capsid
III Biosynthesis
genome replication mRNA production protein synthesis
1. Replication of genome
3. Release
Disintegration : 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
nucleic acids and capsids are assembled together.
2. Maturation
The stage of viral replication at which a virus particle becomes infectious
Standard of Maturation: Having intactness of structure Having property of infectiousness Having antigenicity
I Satellite virus (e.g.virusoid)
Virusoid are small (200-400nt), circular RNA molecules with a rod-like secondary structure which possess no capsid or envelope which are associated with certain plant diseases.
Growth curve
Eclipse: During the biosynthesis; intact virus
particales can not be seen by all means
Logarithmic phase Decline phase
Products of viral replication
progeny genome
early proteins (functional) late mRNA
late proteins (structural)
III assembly、 Maturation 、release
1. Assembly
The stage of replication during which all the structural components come together at one site in the cell and the basic structure of the virus particle is formed.
Viral Interference
1. Concept
2. Probably mechanism
Interferon, IFN blocking or destroying receptors for
virus altering the metabolic pathway of host Defective interfering particle, DIP
I Affected by physical agent Heat ；PH；Radiation
II Affected by chemical agent
III Mechanisms --- Disruption of the lipid-containing envelop --- Modification of proteins --- Modification of DNA
such as heatproteinase K、 ultraviolet 、 DNAase 、 RNAase et.
Structure of PrPC and PrPSC
分子构型
存在部位
存在形式
对蛋白酶K抗性
对去污剂的溶解 性
Endocytosis
Entry via endosomes at the cell surface
2. Uncoating
Nucleic acid has to be sufficiently uncoated that virus replication can begin at this stage.
3. Significances
Benefits---
breaking off disease infected by virus
Disadvantage---
interfere with effect of inoculation of vaccine
Inactivation of viral
II Classification of viruses
By 1995 --71 families, 11 subfamilies --164 genera
For humans and animals --24 families, --DNA: 7; RNA: 17 for humans
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Subvirus
When the nucleic acid is uncoated, infectious virus particles cannot be recovered from the cell - this is the start of the Eclipse phase - which lasts until new infectious virions are made
Their replication strategy like that of viruses they are obligate intracellular parasites.
II viroid
Viroids are small (200-400nt), circular RNA molecules with a rod-like secondary structure which possess no capsid or envelope which are associated with certain plant diseases.
Their replication strategy like that of viruses they are obligate intracellular parasites.
III Prion
--- an infectious factor of protein with no detectable nucleic acid
--- Basic structural unit is prion protein --- PrPc PrPsc while obtaining pathogenicity
and transmissibility --- possesing strong resistant to various factors
I Attachment/Adsorption
1. Ionic attraction
--- at pH7.0 --- temperature-independent. --- non specific --- reversable
2. Receptor combine
Virus attaches to the cell surface. Attachment is via ionic interactions which are temperature-independent.
Principle --- semi-conservative replication Type --- DNA viruses : ds and ss
RNA viruses : ds 、ss and retrovirus
2. Synthesis of proteins
parent genome
early mRNA
Virion Defective virus Abortive infection Integration
Abnormal multiplication
1 . Defective virus
--- containing normal capid proteins --- having mutation or deletion of part of genome --- reproducing with helper virus --- interfering the homologus virus --- HBV and HDV