Virus structure: classification: replication

VIROLOGY
STRUCTURE, CLASSIFICATION & REPLICATION

Thursday, January 26, 2012

TOPICS
• STRUCTURE
• describe and differentiate various viral
structural types and relate to its function
• CLASSIFICATION
• ICTV vs Baltimore classiﬁcation
• REPLICATION
• DNA viruses
• RNA viruses

the structure of viruses


Reference: Chapter 3 Carter And Saunders, 2007

Marilen M. Parungao-Balolong 2011 dvm5.blogspot.com

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

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


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


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

the capsid

THE CAPSID & VIRAL
SYMMETRY

COMPLEX

HELICAL

ICOSAHEDRAL


BASED ON THE
ARCHITECTURE...
Enveloped Viruses

Helical Viruses

Complex
Viruses
Icosahedral Viruses

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

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

CAPSOMERES:
structural polypeptide

✤ The number and
arrangement of the
capsomeres are useful in
identiﬁcation and
classiﬁcation

NOTING THE CAPSID &
THE ENVELOPE..


THE NUCLEIC ACID
CORE


IN RELATION TO
SYMMETRY...
TYPES GENOMES

dsDNA ssDNA dsRNA ssRNA

Icosahedral
(naked)
Icosahedral
(Enveloped)

Helical (naked)

Helical
(Enveloped)


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

BASIS OF
CLASSIFICATION

• SECONDARY:
• replication strategy


NAMING YOUR
VIRUSES


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

REPRESENTATIVE
VIRUSES


Virus Families
 Single-stranded DNA,
nonenveloped viruses
 Parvoviridae
Human parvovirus
Fifth disease
Anemia in
immunocompromised patients

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 13.2 (1 of 20)


 Mastadenovirus
 Respiratory infections in
humans
 Tumors in animals



Double-Stranded DNA, Nonenveloped Viruses
 Mastadenovirus
 Respiratory infections in
humans
 Tumors in animals



 Papillomavirus (human
wart virus)
 Polyomavirus
 Cause tumors; some
cause cancer



Double-Stranded DNA, Nonenveloped Viruses
 Papillomavirus (human
wart virus)
 Polyomavirus
 Cause tumors; some
cause cancer



 Orthopoxvirus (vaccinia
and smallpox viruses)
 Molluscipoxvirus
 Smallpox
 Molluscum contagiosum
 Cowpox



Double-Stranded DNA, Enveloped Viruses
 Orthopoxvirus (vaccinia
and smallpox viruses)
 Molluscipoxvirus
 Smallpox
 Molluscum contagiosum
 Cowpox



 Simplexvirus (HHV1 and HHV 2)
 Varicellavirus (HHV 3)
 Lymphocryptovirus (HHV 4)
 Cytomegalovirus (HHV 5)
 Roseolovirus (HHV 6)
 HHV 7
 Kaposi's sarcoma (HHV 8)
 Some herpesviruses can remain
latent in host cells.



 Hepadnavirus (Hepatitis B
virus)
 Use reverse
transcriptase to produce
DNA from mRNA.



 Hepadnavirus (Hepatitis B
virus)
 Use reverse
DNA from mRNA.



 Enterovirus
 Enteroviruses include
poliovirus and
coxsackievirus.
 Rhinovirus
 Hepatitis A virus



Single-Stranded RNA, + Strand, Nonenveloped

 Enterovirus
 Enteroviruses include
poliovirus and
coxsackievirus.
 Rhinovirus
 Hepatitis A virus



 Hepatitis E virus
 Norovirus causes
gastroenteritis.



Single-Stranded RNA, + Strand, Nonenveloped

 Hepatitis E virus
 Norovirus causes
gastroenteritis.



 Alphavirus
 Alphaviruses are transmitted
by arthropods; include EEE,
WEE.
 Rubivirus (rubella virus)



Single-Stranded RNA, + Strand, Enveloped
 Alphavirus
 Alphaviruses are transmitted
by arthropods; include EEE,
WEE.
 Rubivirus (rubella virus)



 Arboviruses can replicate
in arthropods; include
yellow fever, dengue, SLE,
and West Nile viruses
 Hepatitis C virus



 Coronavirus
 Upper respiratory
infections
 SARS



 Vesiculovirus
 Lyssavirus (rabies virus)
 Cause numerous animal
diseases



Single-Stranded RNA, – Strand,
One RNA Strand
 Vesiculovirus
 Lyssavirus (rabies virus)
 Cause numerous animal
diseases



 Filovirus
 Enveloped, helical
viruses
 Ebola and Marburg
viruses



One RNA Strand
 Filovirus
 Enveloped, helical
viruses
 Ebola and Marburg
viruses



 Paramyxovirus
 Morbillivirus
 Paramyxovirus
 Parainfluenza
 Mumps
 Newcastle disease



One RNA Strand
 Paramyxovirus
 Morbillivirus
 Paramyxovirus
 Parainfluenza
 Mumps
 Newcastle disease



 Hepatitis D virus
 Depends on coinfection
with Hepadnavirus



One RNA Strand
 Hepatitis D virus
 Depends on coinfection
with Hepadnavirus



 Influenzavirus (Influenza
viruses A and B)
 Influenza C virus
 Envelope spikes can
agglutinate RBCs.



Multiple RNA Strands
 Influenzavirus (Influenza
viruses A and B)
 Influenza C virus
 Envelope spikes can
agglutinate RBCs.



 Bunyavirus (CE virus)
 Hantavirus



 Arenavirus
 Helical capsids contain
RNA-containing granules
 Lymphocytic
choriomeningitis
 VEE and Lassa Fever



 Lentivirus (HIV)
 Oncogenic viruses
 Use reverse
DNA from viral genome.
 Includes all RNA tumor
viruses



Single-Stranded RNA, Two RNA Strands,
Produce DNA
 Lentivirus (HIV)
 Oncogenic viruses
 Use reverse
DNA from viral genome.
 Includes all RNA tumor
viruses



 Reovirus (Respiratory
Enteric Orphan)
 Rotavirus
 Mild respiratory infections
and gastroenteritis
 Colorado tick fever



Double-Stranded RNA, Nonenveloped
 Reovirus (Respiratory
Enteric Orphan)
 Rotavirus
 Mild respiratory infections
and gastroenteritis
 Colorado tick fever



virus replication


GROWING VIRUSES

Embryonated
Eggs

Plaques

Cell Culture Parungao-Balolong 2011

LIFE CYCLE


LIFE CYCLE

 Lytic cycle: Phage causes lysis and death of host
cell.
 Lysogenic cycle: Prophage DNA incorporated in host

LIFE CYCLE

 Lytic cycle: Phage causes lysis and death of host cell.
 Lysogenic cycle: Prophage DNA incorporated in
host DNA.

VIRUS MULTIPLICATION


VIRUS MULTIPLICATION (DNA Virus)
• DNA: Cellular enzyme transcribes viral
DNA in nucleus


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.


(- strand RNA Virus)
Attachment

Capsid Nucleus

RNA Cytoplasm

Host cell

Entry
and release


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

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
and release


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


(Retrovirus)

• RNA, reverse transcriptase: Viral enzyme copes viral RNA to
make DNA in cytoplasm Parungao-Balolong 2011

END OF COVERAGE
NEXT MEETING:
MIDTERMS!!!


Virus structure: classification: replication

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