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VIROLOGYSTRUCTURE, 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
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the structure of viruses
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dvm5.blogspot.com
Reference: Chapter 3 Carter And Saunders, 2007
Marilen M. Parungao-Balolong 2011
Thursday, January 26, 2012
dvm5.blogspot.com
Reference: Chapter 3 Carter And Saunders, 2007
Marilen M. Parungao-Balolong 2011
The nucleic acid genome plus the protective protein coat is called the nucleocapsid which may have icosahedral, helical or complex symmetry.
Thursday, January 26, 2012
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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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
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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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the capsid
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THE CAPSID & VIRAL SYMMETRY
COMPLEX
HELICAL
ICOSAHEDRAL
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BASED ON THE ARCHITECTURE...
Helical Viruses
Icosahedral Viruses
Enveloped Viruses
Complex Viruses
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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
Thursday, January 26, 2012
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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CAPSOMERES: structural polypeptide
✤ The number and arrangement of the capsomeres are useful in identification and classification
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NOTING THE CAPSID & THE ENVELOPE..
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THE NUCLEIC ACID CORE
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THE NUCLEIC ACID CORE
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THE NUCLEIC ACID CORE
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THE NUCLEIC ACID CORE
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THE NUCLEIC ACID CORE
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IN RELATION TO SYMMETRY...
TYPES GENOMESGENOMESGENOMESGENOMES
dsDNA ssDNA dsRNA ssRNA
Icosahedral (naked)
Icosahedral (Enveloped)
Helical (naked)
Helical (Enveloped)
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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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BASIS OF CLASSIFICATION
• SECONDARY: • replication strategy
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NAMING YOUR VIRUSES
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HOW ARE THEY NAMED?
• Family names end in -viridae.
• Genus names end in -virus
• Viral species: A group of viruses sharing the same genetic information and ecological niche (host)
• Common names are used for species
• Subspecies are designated by a number
Parungao-Balolong 2011
EXAMPLE Herpesviridae
Herpesvirus
Human herpes virus
EXAMPLE Retroviridae
Lentivirus
Human
immunodeficiency virus
HIV-1, HIV-2
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REPRESENTATIVE VIRUSES
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-stranded DNA,
nonenveloped viruses
Parvoviridae
Human parvovirus
Fifth disease
Anemia in
immunocompromised patients
Table 13.2 (1 of 20)
Virus Families
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-stranded DNA,
nonenveloped viruses
Parvoviridae
Human parvovirus
Fifth disease
Anemia in
immunocompromised patients
Table 13.2 (1 of 20)
Virus Families
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Mastadenovirus
Respiratory infections in
humans
Tumors in animals
Table 13.2 (2 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Double-Stranded DNA, Nonenveloped Viruses
Mastadenovirus
Respiratory infections in
humans
Tumors in animals
Table 13.2 (2 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Papillomavirus (human
wart virus)
Polyomavirus
Cause tumors; some
cause cancer
Table 13.2 (3 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Double-Stranded DNA, Nonenveloped Viruses
Papillomavirus (human
wart virus)
Polyomavirus
Cause tumors; some
cause cancer
Table 13.2 (3 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Orthopoxvirus (vaccinia
and smallpox viruses)
Molluscipoxvirus
Smallpox
Molluscum contagiosum
Cowpox
Table 13.2 (4 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Double-Stranded DNA, Enveloped Viruses
Orthopoxvirus (vaccinia
and smallpox viruses)
Molluscipoxvirus
Smallpox
Molluscum contagiosum
Cowpox
Table 13.2 (4 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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.
Table 13.2 (5 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Double-Stranded DNA, Enveloped Viruses
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.
Table 13.2 (5 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Hepadnavirus (Hepatitis B
virus)
Use reverse
transcriptase to produce
DNA from mRNA.
Table 13.2 (6 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Double-Stranded DNA, Enveloped Viruses
Hepadnavirus (Hepatitis B
virus)
Use reverse
transcriptase to produce
DNA from mRNA.
Table 13.2 (6 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Enterovirus
Enteroviruses include
poliovirus and
coxsackievirus.
Rhinovirus
Hepatitis A virus
Table 13.2 (7 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, + Strand, Nonenveloped
Enterovirus
Enteroviruses include
poliovirus and
coxsackievirus.
Rhinovirus
Hepatitis A virus
Table 13.2 (7 of 20)
Thursday, January 26, 2012
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Hepatitis E virus
Norovirus causes
gastroenteritis.
Table 13.2 (8 of 20)
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, + Strand, Nonenveloped
Hepatitis E virus
Norovirus causes
gastroenteritis.
Table 13.2 (8 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Alphavirus
Alphaviruses are transmitted
by arthropods; include EEE,
WEE.
Rubivirus (rubella virus)
Table 13.2 (9 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, + Strand, Enveloped
Alphavirus
Alphaviruses are transmitted
by arthropods; include EEE,
WEE.
Rubivirus (rubella virus)
Table 13.2 (9 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Arboviruses can replicate
in arthropods; include
yellow fever, dengue, SLE,
and West Nile viruses
Hepatitis C virus
Table 13.2 (10 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, + Strand, Enveloped
Arboviruses can replicate
in arthropods; include
yellow fever, dengue, SLE,
and West Nile viruses
Hepatitis C virus
Table 13.2 (10 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Coronavirus
Upper respiratory
infections
SARS
Table 13.2 (11 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, + Strand, Enveloped
Coronavirus
Upper respiratory
infections
SARS
Table 13.2 (11 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Vesiculovirus
Lyssavirus (rabies virus)
Cause numerous animal
diseases
Table 13.2 (12 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, One RNA Strand Vesiculovirus
Lyssavirus (rabies virus)
Cause numerous animal
diseases
Table 13.2 (12 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Filovirus
Enveloped, helical
viruses
Ebola and Marburg
viruses
Table 13.2 (13 of 20)
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, One RNA Strand Filovirus
Enveloped, helical
viruses
Ebola and Marburg
viruses
Table 13.2 (13 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Paramyxovirus
Morbillivirus
Paramyxovirus
Parainfluenza
Mumps
Newcastle disease
Table 13.2 (14 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, One RNA Strand Paramyxovirus
Morbillivirus
Paramyxovirus
Parainfluenza
Mumps
Newcastle disease
Table 13.2 (14 of 20)
Thursday, January 26, 2012
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Hepatitis D virus
Depends on coinfection
with Hepadnavirus
Table 13.2 (15 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, One RNA Strand Hepatitis D virus
Depends on coinfection
with Hepadnavirus
Table 13.2 (15 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Influenzavirus (Influenza
viruses A and B)
Influenza C virus
Envelope spikes can
agglutinate RBCs.
Table 13.2 (16 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, Multiple RNA Strands Influenzavirus (Influenza
viruses A and B)
Influenza C virus
Envelope spikes can
agglutinate RBCs.
Table 13.2 (16 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings UN 13.3
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Crossing the Species Barrier
UN 13.3
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Bunyavirus (CE virus)
Hantavirus
Table 13.2 (17 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, Multiple RNA Strands Bunyavirus (CE virus)
Hantavirus
Table 13.2 (17 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Arenavirus
Helical capsids contain
RNA-containing granules
Lymphocytic
choriomeningitis
VEE and Lassa Fever
Table 13.2 (18 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, – Strand, Multiple RNA Strands Arenavirus
Helical capsids contain
RNA-containing granules
Lymphocytic
choriomeningitis
VEE and Lassa Fever
Table 13.2 (18 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Lentivirus (HIV)
Oncogenic viruses
Use reverse
transcriptase to produce
DNA from viral genome.
Includes all RNA tumor
viruses
Table 13.2 (19 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Single-Stranded RNA, Two RNA Strands, Produce DNA Lentivirus (HIV)
Oncogenic viruses
Use reverse
transcriptase to produce
DNA from viral genome.
Includes all RNA tumor
viruses
Table 13.2 (19 of 20)
Thursday, January 26, 2012
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Reovirus (Respiratory
Enteric Orphan)
Rotavirus
Mild respiratory infections
and gastroenteritis
Colorado tick fever
Table 13.2 (20 of 20)
Thursday, January 26, 2012
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Double-Stranded RNA, Nonenveloped
Reovirus (Respiratory
Enteric Orphan)
Rotavirus
Mild respiratory infections
and gastroenteritis
Colorado tick fever
Table 13.2 (20 of 20)
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virus replication
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GROWING VIRUSES
Parungao-Balolong 2011
Plaques
Cell Culture
Embryonated Eggs
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LIFE CYCLE
Parungao-Balolong 2011Thursday, January 26, 2012
LIFE CYCLE
Parungao-Balolong 2011Thursday, January 26, 2012
LIFE CYCLE
Parungao-Balolong 2011
Lytic cycle: Phage causes lysis and death of host
cell. Lysogenic cycle: Prophage DNA incorporated in host
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LIFE CYCLE
Parungao-Balolong 2011
Lytic cycle: Phage causes lysis and death of host cell.
Lysogenic cycle: Prophage DNA incorporated in
host DNA.Thursday, January 26, 2012
VIRUS MULTIPLICATION
Parungao-Balolong 2011Thursday, January 26, 2012
VIRUS MULTIPLICATION
Parungao-Balolong 2011Thursday, January 26, 2012
VIRUS MULTIPLICATION (DNA Virus)
Parungao-Balolong 2011
• DNA: Cellular enzyme transcribes viral DNA in nucleus
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VIRUS MULTIPLICATION : (+ strand RNA Virus)
Parungao-Balolong 2011
Maturationand release
Entryand uncoating
Translation and synthesisof viral proteins
RNA replication by viral RNA-dependent RNA polymerase
Uncoating releasesviral RNA and proteins.
Nucleus
Attachment
Viralprotein
Capsidprotein
Cytoplasm
Host cell
– strand is transcribedfrom + viral genome.
+ strand
mRNA is transcribedfrom the – strand.
Capsid
RNA
Viralgenome(RNA)
ssRNA; +or sense strand;Picornaviridae
(a)
• RNA, + strand: Viral RNA is a template for synthesis of RNA polymerase.
Thursday, January 26, 2012
VIRUS MULTIPLICATION (- strand RNA Virus)
Parungao-Balolong 2011
Maturationand release
Entryand uncoating
Translation and synthesisof viral proteins
RNA replication by viral RNA-dependent RNA polymerase
Uncoating releasesviral RNA and proteins.
Nucleus
Attachment
Viralprotein
Capsidprotein
Cytoplasm
Host cell
– strands areincorporatedinto capsid
The + strand (mRNA) must firstbe transcribed from the – viralgenome before proteins canbe synthesized.
Additional – strands aretranscribed from mRNA.
Capsid
RNA
Viralgenome(RNA)
ssRNA; – orantisense strand;Rhabdoviridae
(b)
• RNA – strand: Viral enzyme copies viral RNA to make mRNA in cytoplasm
Thursday, January 26, 2012
VIRUS MULTIPLICATION : (dsRNA Virus)
Parungao-Balolong 2011
Maturationand release
Entryand uncoating
Translation and synthesisof viral proteins
RNA replication by viral RNA-dependent RNA polymerase
Uncoating releasesviral RNA and proteins.
Nucleus
Attachment
Viralprotein
RNA polymerase initiates production of– strands. The mRNA and – strands form thedsRNA that is incorporated as new viral genome.
Cytoplasm
Host cell
mRNA is produced inside thecapsid and released into thecytoplasm of the host.
Capsid
RNA
Viralgenome(RNA)
dsRNA; + or sensestrand with – or antisense strand; Reoviridae
Capsid proteins and RNA-dependent RNA polymerase
(c)
• RNA, double-stranded: Viral enzyme copies – strand RNA to make mRNA in cytoplasm
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VIRUS MULTIPLICATION (Retrovirus)
Parungao-Balolong 2011• RNA, reverse transcriptase: Viral enzyme copes viral RNA to
make DNA in cytoplasmThursday, January 26, 2012
END OF COVERAGE
NEXT MEETING: MIDTERMS!!!
Thursday, January 26, 2012