Viral Reolication Flashcards by Iseoluwa Ojo

When a virus infects a cell, ______ must be uncoated and must gain access to __________

nucleic acid

metabolic machinery of cell.

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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

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some complex viruses (HSV) may have more than one species of anti-receptor molecule

T/F

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Penetration of a virus into a cell is not an energy-dependent step

T/F

It is

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Penetration of a virus into a cell occurs ________ after _________

almost instantaneously after attachment

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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

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Uncoating of a virus

Can occur at ________ or ———

same time as penetration

shortly after

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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

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After uncoating of the virus

There should be _________ and ___________

Expression of viral genome

synthesis of viral components

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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

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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

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Assembly and Release of virus

Components of _____ synthesis directed by _________

______ stage of infection

capsid; late genes

Final

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Assembly of enveloped viruses needs interaction with ________ which has been ________

plasma membrane

modified

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Assembly and Release of virus

Enveloped viruses released _______ by __________ or _____

Naked viruses _______ in _______ and released during ______

gradually

budding or exocytosis

accumulate in cytoplasm ; lysis

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Factors in Viral Pathogenesis

______ of the infecting virus

Effects of viral infection on ____ (Cellular ______)

Entry into the Host

Virulence

Cells; Pathogenesis

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Factors in Viral Pathogenesis

_______ of Infection

Cell/Tissue ______

Cell/Tissue _______

______-____ Response

Virus _________ or ______

Course

Tropism

Damage

Host Immune

Clearance or Persistence

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Course of Viral Infection

________

_______

Primary Replication

Systemic Spread

Secondary Replication

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Course of Viral Infection
Primary Replication
The place of primary replication is where the virus replicates after ____________

gaining initial entry into the host.

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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.

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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.

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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