Virus Replication Flashcards
Host tropism
Influenza A:
causes
epidemics and
occasionally
pandemics, and
there are animal
reservoirs, (birds;
pigs…)
Most bird variants
cannot infect
humans
Local vs widespread
e.g. Human Papilloma
Virus (HPV)
- Commonly cause local
infections Warts;
Verrucae;
Measles virus migrates
to lymphatic tissues then
disseminates to many
epithelial sites
Tissue tropism
E.g.influenza virus –
restricted to respiratory
epithelial cells
Rabies – spreads to
brain, then salivary
glands via peripheral
nerves
Sites of infection
Respiratory Gastro-intestinal Dermal (Skin)
Stages of viral replication
Stages of viral replication
[1.] Adsorption
[2.] Entry
[3.] Uncoating
[4.] Replication /synthesis
[5.] Assembly
[6.] Exit
Bacteriophages (bacterial viruses)
- Bacteriophage = “Bacteria eater”
- Tail fibres bind to specific
surface receptors and - Phage genome is injected into
susceptible bacterial host - Phage replication occurs in the
cytoplam - Phages encode enzymes to
trigger bacterial cell lysis
Phage Replication Summary
[1] Adsorption - Phage tail fibres
[2-3] Entry & Uncoating- Injection of genome through bacterial surface receptors
[4] Replication & synthesis– Lysis / Lysogeny
[5] Assembly– New phage particle in cytoplasm
[6] Exit- Phage-encoded lysis
[1.] Adsorption
A.Bacteriophage-Tail fibers
with viral attachment proteins
B. Enveloped virus (Influenza virus)-Attachment spike embedded in
viral envelope
C. Non-enveloped virus (Adenovirus)-Attachment spike extending from viral capsid
D. Non-enveloped virus (Poliovirus)-Attachment protein as part of viral
capsid
SARS-CoV-2 Spike (S) protein
Some variants may
recognise or bind-to the
receptor more or less
easily
Do S protein variants
affect immune
response / vaccine
efficiency?
Slightly lower antibody
recognition of B.1.351,
but vaccine still
considered effective
[2&3] Entry & Uncoating
There are multiple different mechanisms of viral
entry into eukaryotic cells and uncoating
The type of entry depends on:
The viral structure
Enveloped / non-enveloped
Or the host cell
Availability of suitable receptors
[i] Replication: dsDNA viruses
DNA replication and
transcription must
occur in the nucleus
Translation occurs in
the cytoplasm
Assembly occurs in
the nucleus
e.g. Herpes viruses
Can also exist as a
dormant episome in
neurones - latency
RNA Virus replication (+ / – sense)
- Positive sense (5’ – 3’) e.g. Polio virus
Acts as mRNA and can be directly translated into viral
proteins - Negative sense (3’-5’) e.g. Influenza virus
Must be converted to the complimentary positive sense
by RNA polymerase before translation - Influenza = negative sense RNA genome (ssRNA-)
and carries an RNA polymerase in the virion for
conversion on entry into cells.
[ii] Replication: RNA+ viruses
RNA replication and
translation occur in
the cytoplasm
e.g. Poliovirus
Viral encoded RNA
polymerase creates
negative strand for
genome replication
Coat proteins
translated from new
copies of + strand
[iii] Replication: RNA- viruses
Positive strand is
transcribed in the
cytoplasm for
translation of coat
proteins
Virion carries an RNA
polymerase
e.g. Influenza virus
Positive strand acts
as a template for
replication of
Negative strand
genomes
[iv] Replication: Retroviruses
HIV (2 x +ssRNA)
Virion carries reverse
transcriptase and integrase
enzymes
Reverse transcriptase
converts RNA to DNA in the
cytoplasm
DNA is integrated into the
host chromosome in the
nucleus (provirus) which is
transcribed by host
[5&6]- Assembly and Exit
The mechanism of exit (egress) also depends on virus
type and host cell type.
* Enveloped viruses send viral proteins to the host cell
plasma membrane, dock to them, and ‘bud’ out of the cell,
taking a portion of the plasma membrane with them.
* Naked viruses often exit a cell by lysis.
* Plant viruses may move from cell to cell within one plant
via specific cytoplasmic connections.
HIV – Budding from the
membrane
Viral Replication Summary
DNA Viruses-Replication in nucleus
RNA Viruses-Replication in cytoplasm
Retro Viruses-Replication of provirus in
nucleus
Eukaryotic Virus Replication Summary
[1] Adsorption- Specific virus – cell receptor binding
[2-3] Entry & Uncoating– Multiple mechanisms (endocytosis /
fusion/ damage)
[4] Replication & synthesis-Method depends on genome type
[5] Assembly– In nucleus / cytoplasm
[6] Exit- Lysis / budding
