6. Attachment
First step to initiate infectionFirst step to initiate infection
Receptor ligand interaction
Ligand on virus surfaceLigand on virus surface
Host cell receptors
This virus‐cell interaction determines the host
range and tissue tropism of the viruses
Viruses might have more than one ligand and may g g y
bind to various cell receptors in sequential order
Replication of viruses
7. Attachment
Initial viral attachment to cells is through a fewInitial viral attachment to cells is through a few
receptors
Weak
Reversible
When attachment to sufficient receptors
Strong
Irreversible
Replication of viruses
14. Entry/Penetrationy/
All animal viruses must cross the plasmaAll animal viruses must cross the plasma
membrane of the cells
Some viruses must cross the nuclear envelop,Some viruses must cross the nuclear envelop,
usually via nuclear pore
Replication of viruses
30. Central dogma of molecular biology g gy
The flow of genetic information is always from DNA to RNA and thenThe flow of genetic information is always from DNA to RNA and then
to protein, with genetic information transmitted from one generation
to the next through copying from DNA to DNA
Replication of viruses
33. Transcriptionp
The viruses that replicate in nucleus uses cellularThe viruses that replicate in nucleus uses cellular
enzymes while the ones that replicate in cytoplasm
encode their own
All viruses that carry out transcription in the
cytoplasm (except the plus strand RNA viruses) havecytoplasm (except the plus‐strand RNA viruses) have
the transcriptases packed in the virion
Replication of viruses
40. RNA viruses that do NOT have a DNA phase
Genome RNA-dependent Infectivity of Initial event in
RNA viruses that do NOT have a DNA phase
Genome RNA dependent
RNA polymerase
(=transcriptase)
IN VIRION
Infectivity of
RNA
Initial event in
cell
Plus-stranded
RNA
No Infectious Translation
Negative-
stranded RNA
Yes Non-infectious Transcription
Double-
stranded RNA
Yes Non-infectious Transcription
Replication of viruses 40
45. Types of transcription and translation
Early transcription and translation:Early transcription and translation:
Virus enzymes required for
TranscriptionTranscription
Shut down of cellular function
Late transcription and translation:Late transcription and translation:
Structural proteins
Virus associated enzymesVirus associated enzymes
Replication of viruses
46. Categories of proteins encoded by the viruses
Structural proteins of viruses S uc u a p o e s o uses
Virus associated enzymes (transcriptases)
Non structural proteins mainly enzymes required for
transcription, replication of NA and cleavage
Regulatory proteins that control the temporal expression
of viral genome
Proteins down regulating the expression of cellular
genome
Replication of viruses
47. Categories of proteins encoded by the viruses
Oncogene products (Oncoproteins) and inactivators of O coge e p oduc s (O cop o e s) a d ac a o s o
cellular tumor suppressors
Proteins influencing viral virulence host range tissueProteins influencing viral virulence, host range, tissue
tropism etc
Virokines, act on noninfected cells to modulate the
progress of infection in the host
Replication of viruses