Viral Reolication Flashcards
When a virus infects a cell, ______ must be uncoated and must gain access to __________
nucleic acid
metabolic machinery of cell.
Attachment of a virus
specific binding of a ___ protein (the ________) to a constituent of the cell surface (the ______)
e.g.__________ of influenza virus
virion
anti-receptor
receptor
hemagglutinin
some complex viruses (HSV) may have more than one species of anti-receptor molecule
T/F
T
Penetration of a virus into a cell is not an energy-dependent step
T/F
F
It is
Penetration of a virus into a cell occurs ________ after _________
almost instantaneously after attachment
After the virus attaches to the host cell, it can enter the cell by several mechanisms:
(1) Transfer of ________ across the cell membrane by ______
(2) Transfer of _________ through the cell membrane
(3) ______________ with the host cell membrane
the entire viral particle ; endocytosis
only the viral genome
Fusion of the viral envelope
Uncoating of a virus
Can occur at ________ or ———
same time as penetration
shortly after
Uncoating of a virus
Is the _________ of ________ from _______
Released as:
________(_____)
as ________ (______)
separation of viral nucleic acid (n.a.)
outer structural components
free n.a.; picornaviruses
nucleocapsid; reoviruses
After uncoating of the virus
There should be _________ and ___________
Expression of viral genome
synthesis of viral components
After the viral nucleic acid is released inside the host cell:
The ________ and ———- processes of the host cell are redirected for the production of ______ and _______
transcription and translation
viral proteins and nucleic acids
The different types of nucleic acid genomes are expressed and replicated in several ways:
DNA genomes undergo replication-using ________________
RNA genomes may be +ssRNA; Can be ____________ or _________
RNA genomes may also be -ssRNA; The RNA must ____________________
processes similar to cellular replication
read directly as an mRNA or reverse transcribed by reverse transcriptase into DNA
first be used as a template to form +mRNAs
Assembly and Release of virus
Components of _____ synthesis directed by _________
______ stage of infection
capsid; late genes
Final
Assembly of enveloped viruses needs interaction with ________ which has been ________
plasma membrane
modified
Assembly and Release of virus
Enveloped viruses released _______ by __________ or _____
Naked viruses _______ in _______ and released during ______
gradually
budding or exocytosis
accumulate in cytoplasm ; lysis
Factors in Viral Pathogenesis
______ of the infecting virus
Effects of viral infection on ____ (Cellular ______)
Entry into the Host
Virulence
Cells; Pathogenesis
Factors in Viral Pathogenesis
_______ of Infection
Cell/Tissue ______
Cell/Tissue _______
______-____ Response
Virus _________ or ______
Course
Tropism
Damage
Host Immune
Clearance or Persistence
Course of Viral Infection
________
_______
_______
Primary Replication
Systemic Spread
Secondary Replication
Course of Viral Infection
Primary Replication
The place of primary replication is where the virus replicates after ____________
gaining initial entry into the host.
Course of Viral Infection
This frequently determines whether the infection will be __________ or _____________
localized at the site of entry
spread to become a systemic infection.
Course of Viral Infection
Systemic Spread
Apart from direct cell-to-cell contact, the virus may _____________ and ______
spread via the blood stream and the CNS.
Course of Viral Infection
Secondary Replication
Secondary replication takes place at ______________ following ________
susceptible organs/tissues following systemic spread.
Viral Virulence
The ability of a virus to ______ in an infected host
cause disease
A ______ strain causes significant disease
While
_________________ strain causes no or
reduced disease
virulent
An avirulent or attenuated
Virulence depends on
_____
Virus _____ (genetics)
___________________
_______ factors -
Dose
strain
Inoculation route - portal of entry
Host
Cell Tropism
Viral _____ for ____________
affinity
specific body tissues
Cell Tropism
is determined by
Cell _______ for virus.
Cell ________ that recognize viral promoters and enhancer sequences.
Ability of the cell to __________.
receptors
transcription factors
support virus replication
Cell Tropism
is determined by
_______ barriers.
Local ______,___,______
enzymes and non- specific factors in —————
_____ enzymes and ____ in the gastrointestinal tract that may inactivate some viruses.
Physical
temperature, pH, and oxygen tension
body secretions
Digestive; bile
Viruses may replicate widely throughout the body without any disease symptoms if they do not cause _________
significant cell damage or death.
Cell Damage
Picornaviruses cause ___________ the cells in which they replicate, leading to ____ and increased ____ secretion in the case of Rhinoviruses, then paralysis or death (usually due to ______ failure) for Poliovirus .
lysis and death of
fever.; mucus
respiratory
Retroviruses do not generally cause cell death
T/F
With reason
T
Because they released from the cell by budding rather than by cell lysis, and cause persistent infections.
The _______ to the virus probably has the greatest impact on the outcome of infection.
immune response
Immune Response
In the most cases, the virus is ______ from the body and results in ______
In other infections, the immune response is unable to ____________ and the virus _____.
Cleared completely; complete recovery.
clear the virus completely; persists
In general, ______ immunity plays the major role in clearing virus infection whereas ______ immunity protects against reinfection.
cellular
humoral
Immune Pathological Response
Enhanced viral injury could be due to one or a mixture of the following mechanisms;-
Increased _________ to Tc cells e.g. HBV
Specific _________ or ___________
Binding of _______ virus
Immune _______ in organs such as the skin, brain or kidney e.g. ____ of rubella and measles.
secondary response
ADCC or complement mediated cell lysis
un-neutralized
complex deposition; rash
Immune Pathological Response
Binding of un-neutralized virus- ____ complexes to cell surface ___ receptors, and thus _______________ e.g. ______ haemorrhagic fever, _____.
Antibody ; Fc
increasing the number of cells infected
Dengue; HIV
Viral Clearance or Persistence
There are 2 types of chronic persistent infections.
_________
________
True Latency
Persistence
The majority of viral infections are ______ but certain viruses may cause ________
cleared
persistent infections.
Viral Clearance or Persistence
True Latency - the virus ____________________________ e.g. HSV, VZV. Its genome may be _______ or _________
remains completely latent following primary infection
integrated into the cellular genome or exists as episomes.
Viral Clearance or Persistence
Persistence - the virus __________ in the body at a ________ level e.g. ___,_____,____ ____
replicates continuously
very low
HIV, HBV, CMV, EBV.
Mechanisms of Viral Persistence
______ variation
_______ tolerance
restricted __________
antigenic
Immune
gene expression
Mechanism of viral persistence
immune tolerance- causing ___________, may be due to _____ factors, _______ infection,_________
a reduced response to an antigen
genetic
pre-natal
molecular mimicry
Mechanisms of Viral Persistence
down-regulation of _______________, resulting in ____________
e.g.
_____viruses
MHC class I expression
lack of recognition of infected cells
Adeno
Mechanisms of Viral Persistence
down-regulation of accessory molecules involved in _________ e.g. _____ and _____ by ____.
infection of immunopriviliged sites within the body e.g. ____ in _______ in _____
direct infection of the cells of the ________ e.g. ______ viruses, _______ - often resulting in __________.
immune recognition
LFA-3 and ICAM-1 ; EBV
HSV ; sensory ganglia in the CNS
immune system itself
Herpes; Retroviruses (HIV) ; immunosuppression
Matrix proteins connect _____ to ——-
envelope to capsid
Vaccinia virus = _____ virus
B19 = ——-
pox
parvo
Robo- ———
Arbo - __________
rodent
arthropods
Baltimore classification
The division of the viruses into classes based on _______ and ________
Suggested by ______ – ____ Baltimore classes.
genome type
mode of replication and transcription
David Baltimore
Seven
Baltimore classification
CLASS1-
CLASS2-
CLASS3-
CLASS4-
CLASS5-
CLASS6-
CLASS7-
Double stranded DNA
Single stranded DNA
Double stranded RNA
single stranded RNA plus sense
Single stranded RNA minus sense
Single stranded RNA that replicated with DNA intermediate
Double stranded DNA that replicated with RNA intermediate
In the Baltimore classification, which classes have examples fo bacterial viruses
Class 1-4
Early mRNA codes for ?
Late mRNA codes for ?
Proteins to ensure it’s infectivity . Eg proteins to shut off host cell, or replicate viral genome
Structural proteins . Eg capsid
