"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack
Virus structure: classification: replication
1. VIROLOGY
STRUCTURE, CLASSIFICATION & REPLICATION
Thursday, January 26, 2012
2. TOPICS
• STRUCTURE
• describe and differentiate various viral
structural types and relate to its function
• CLASSIFICATION
• ICTV vs Baltimore classification
• REPLICATION
• DNA viruses
• RNA viruses
Thursday, January 26, 2012
4. Reference: Chapter 3 Carter And Saunders, 2007
Marilen M. Parungao-Balolong 2011 dvm5.blogspot.com
Thursday, January 26, 2012
5. Reference: Chapter 3 Carter And Saunders, 2007
The nucleic acid genome plus the
protective protein coat is called the
nucleocapsid which may have
icosahedral, helical or complex symmetry.
Marilen M. Parungao-Balolong 2011 dvm5.blogspot.com
Thursday, January 26, 2012
6. the envelope
• Enveloped viruses obtain their
envelope by budding through
a host cell membrane
• In some cases, the virus buds
through the plasma
membrane but in other cases
the envelope may be derived
from internal cell membranes
such as those of the Golgi
body or the nucleus
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7. the envelope
• Enveloped viruses do not
necessarily have to kill their
host cell in order to be
released, since they can bud
out of the cell - a process
that is not necessarily lethal
to the cell - hence some
budding viruses can set up
persistent infections
Thursday, January 26, 2012
8. the envelope
• Enveloped viruses are readily
infectious only if the envelope
is intact (since the viral
attachment proteins which
recognize the host cell
receptors are in the viral
envelope)
• This means that agents that
damage the envelope, such as
alcohols and detergents,
reduce infectivity
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10. THE CAPSID & VIRAL
SYMMETRY
COMPLEX
HELICAL
ICOSAHEDRAL
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11. BASED ON THE
ARCHITECTURE...
Enveloped Viruses
Helical Viruses
Complex
Viruses
Icosahedral Viruses
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12. ICOSAHEDRAL
CAPSID
• Icosahedral morphology is
characteristic of the
nucleocapsids of many
“spherical” viruses
• The icosahedral capsid
structure of adenovirus is
made up of three proteins,
hexon, penton base, and fiber
• Some proteins are associated
with viral DNA, whereas
others are associated with
hexon and are involved in
the formation of the capsid
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13. HELICAL
CAPSID
• The icosahedral capsid structure
of adenovirus is made up of
three proteins, hexon, penton
base, and fiber
• Helical morphology is seen in
nucleocapsids of many
filamentous and pleomorphic
viruses
• Helical nucleocapsids are
characterized by length, width,
pitch of the helix, and number of
protomers per helical turn
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14. CAPSOMERES:
structural polypeptide
✤ The number and
arrangement of the
capsomeres are useful in
identification and
classification
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21. IN RELATION TO
SYMMETRY...
TYPES GENOMES
dsDNA ssDNA dsRNA ssRNA
Icosahedral
(naked)
Icosahedral
(Enveloped)
Helical (naked)
Helical
(Enveloped)
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22. BASIS OF
CLASSIFICATION
• PRIMARY: nature of their genome and
their structure
• NUCLEIC ACID
• RNA or DNA (single-stranded or double-stranded; non-
segmented or segmented; linear or circular; if genome is
single stranded RNA, can it function as mRNA?; whether
genome is diploid (such as in retroviruses)
• VIRION STRUCTURE ( symmetry (icosahedral, helical,
complex); enveloped or not enveloped; number of
capsomeres
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23. BASIS OF
CLASSIFICATION
• SECONDARY:
• replication strategy
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32. NAMING YOUR
VIRUSES
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33. HOW ARE THEY NAMED?
• Family names end in -viridae. EXAMPLE
Herpesviridae
• Genus names end in -virus Herpesvirus
• Viral species: A group of Human herpes virus
viruses sharing the same
genetic information and EXAMPLE
ecological niche (host)
Retroviridae
• Common names are used Lentivirus
for species Human
immunodeficiency virus
• Subspecies are designated HIV-1, HIV-2
by a number
Parungao-Balolong 2011
Thursday, January 26, 2012
79. LIFE CYCLE
Parungao-Balolong 2011
Thursday, January 26, 2012
80. LIFE CYCLE
Parungao-Balolong 2011
Thursday, January 26, 2012
81. LIFE CYCLE
Lytic cycle: Phage causes lysis and death of host
cell.
Lysogenic cycle: Prophage DNA incorporated in host
Parungao-Balolong 2011
Thursday, January 26, 2012
82. LIFE CYCLE
Lytic cycle: Phage causes lysis and death of host cell.
Lysogenic cycle: Prophage DNA incorporated in
host DNA.
Parungao-Balolong 2011
Thursday, January 26, 2012
85. VIRUS MULTIPLICATION (DNA Virus)
• DNA: Cellular enzyme transcribes viral
DNA in nucleus
Parungao-Balolong 2011
Thursday, January 26, 2012
86. VIRUS MULTIPLICATION : (+ strand RNA Virus)
•RNA, + strand:Viral RNA is a template for synthesis of
RNA polymerase.
Attachment
Capsid
Nucleus
RNA
Cytoplasm
Host cell
Entry
Maturation and uncoating
and release
Translation and synthesis RNA replication by viral RNA-
of viral proteins dependent RNA polymerase
Uncoating releases
– strand is transcribed viral RNA and proteins.
from + viral genome.
Capsid Viral Viral
protein genome protein
(RNA)
(a) ssRNA; +
+ strand or sense strand;
Picornaviridae
mRNA is transcribed
from the – strand.
Parungao-Balolong 2011
Thursday, January 26, 2012
87. VIRUS MULTIPLICATION
(- strand RNA Virus)
Attachment
Capsid Nucleus
RNA Cytoplasm
Host cell
Entry
Maturation and uncoating
and release
Translation and synthesis RNA replication by viral RNA-
of viral proteins dependent RNA polymerase
Uncoating releases
viral RNA and proteins.
The + strand (mRNA) must first
be transcribed from the – viral
Viral Viral
genome before proteins can
genome protein
be synthesized.
(RNA)
Capsid
protein
(b) ssRNA; – or
– strands are antisense strand;
incorporated Rhabdoviridae
into capsid Additional – strands are
transcribed from mRNA.
• RNA – strand:Viral enzyme copies viral RNA to
make mRNA in cytoplasm Parungao-Balolong 2011
Thursday, January 26, 2012
88. VIRUS MULTIPLICATION : (dsRNA Virus)
• RNA, double-stranded:Viral enzyme copies – strand
RNA to make mRNA in cytoplasm
Attachment
Capsid Nucleus
RNA
Cytoplasm
Host cell
Entry
Maturation and uncoating
and release
Translation and synthesis RNA replication by viral RNA-
of viral proteins dependent RNA polymerase
Uncoating releases
RNA polymerase initiates production of mRNA is produced inside the viral RNA and proteins.
– strands. The mRNA and – strands form the capsid and released into the
dsRNA that is incorporated as new viral genome. cytoplasm of the host. Viral
Viral
genome protein
(RNA)
(c) dsRNA; + or sense
Capsid proteins and RNA- strand with – or
dependent RNA polymerase antisense strand;
Reoviridae
Parungao-Balolong 2011
Thursday, January 26, 2012
89. VIRUS MULTIPLICATION
(Retrovirus)
• RNA, reverse transcriptase: Viral enzyme copes viral RNA to
make DNA in cytoplasm Parungao-Balolong 2011
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90. END OF COVERAGE
NEXT MEETING:
MIDTERMS!!!
Thursday, January 26, 2012