Virus structure: classification: replication

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


the structure of viruses


dvm5.blogspot.com

Reference: Chapter 3 Carter And Saunders, 2007

Marilen M. Parungao-Balolong 2011


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.


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...

Helical Viruses

Icosahedral Viruses

Enveloped Viruses

Complex 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 GENOMESGENOMESGENOMESGENOMES

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.

• 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


REPRESENTATIVE VIRUSES


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



Mastadenovirus

Respiratory infections in

humans

Tumors in animals

Table 13.2 (2 of 20)



Double-Stranded DNA, Nonenveloped Viruses

Mastadenovirus

Respiratory infections in

humans

Tumors in animals

Table 13.2 (2 of 20)



Papillomavirus (human

wart virus)

Polyomavirus

Cause tumors; some

cause cancer

Table 13.2 (3 of 20)



Double-Stranded DNA, Nonenveloped Viruses

Papillomavirus (human

wart virus)

Polyomavirus

Cause tumors; some

cause cancer

Table 13.2 (3 of 20)



Orthopoxvirus (vaccinia

and smallpox viruses)

Molluscipoxvirus

Smallpox

Molluscum contagiosum

Cowpox

Table 13.2 (4 of 20)



Double-Stranded DNA, Enveloped Viruses

Orthopoxvirus (vaccinia

and smallpox viruses)

Molluscipoxvirus

Smallpox

Molluscum contagiosum

Cowpox

Table 13.2 (4 of 20)



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)



Hepadnavirus (Hepatitis B

virus)

Use reverse

transcriptase to produce

DNA from mRNA.

Table 13.2 (6 of 20)




Hepadnavirus (Hepatitis B

virus)

Use reverse


DNA from mRNA.

Table 13.2 (6 of 20)



Enterovirus

Enteroviruses include

poliovirus and

coxsackievirus.

Rhinovirus

Hepatitis A virus

Table 13.2 (7 of 20)



Single-Stranded RNA, + Strand, Nonenveloped

Enterovirus

Enteroviruses include

poliovirus and

coxsackievirus.

Rhinovirus

Hepatitis A virus

Table 13.2 (7 of 20)



Hepatitis E virus

Norovirus causes

gastroenteritis.

Table 13.2 (8 of 20)



Single-Stranded RNA, + Strand, Nonenveloped

Hepatitis E virus

Norovirus causes

gastroenteritis.

Table 13.2 (8 of 20)



Alphavirus

Alphaviruses are transmitted

by arthropods; include EEE,

WEE.

Rubivirus (rubella virus)

Table 13.2 (9 of 20)



Single-Stranded RNA, + Strand, Enveloped

Alphavirus

Alphaviruses are transmitted

by arthropods; include EEE,

WEE.

Rubivirus (rubella virus)

Table 13.2 (9 of 20)



Arboviruses can replicate

in arthropods; include

yellow fever, dengue, SLE,

and West Nile viruses

Hepatitis C virus

Table 13.2 (10 of 20)



Coronavirus

Upper respiratory

infections

SARS

Table 13.2 (11 of 20)



Vesiculovirus

Lyssavirus (rabies virus)

Cause numerous animal

diseases

Table 13.2 (12 of 20)



Single-Stranded RNA, – Strand, One RNA Strand Vesiculovirus

Lyssavirus (rabies virus)

Cause numerous animal

diseases

Table 13.2 (12 of 20)



Filovirus

Enveloped, helical

viruses

Ebola and Marburg

viruses

Table 13.2 (13 of 20)



Single-Stranded RNA, – Strand, One RNA Strand Filovirus

Enveloped, helical

viruses

Ebola and Marburg

viruses

Table 13.2 (13 of 20)



Paramyxovirus

Morbillivirus

Paramyxovirus

Parainfluenza

Mumps

Newcastle disease

Table 13.2 (14 of 20)



Single-Stranded RNA, – Strand, One RNA Strand Paramyxovirus

Morbillivirus

Paramyxovirus

Parainfluenza

Mumps

Newcastle disease

Table 13.2 (14 of 20)



Hepatitis D virus

Depends on coinfection

with Hepadnavirus

Table 13.2 (15 of 20)



Single-Stranded RNA, – Strand, One RNA Strand Hepatitis D virus

Depends on coinfection

with Hepadnavirus

Table 13.2 (15 of 20)



Influenzavirus (Influenza

viruses A and B)

Influenza C virus

Envelope spikes can

agglutinate RBCs.

Table 13.2 (16 of 20)



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)



Crossing the Species Barrier

UN 13.3



Bunyavirus (CE virus)

Hantavirus

Table 13.2 (17 of 20)



Single-Stranded RNA, – Strand, Multiple RNA Strands Bunyavirus (CE virus)

Hantavirus

Table 13.2 (17 of 20)



Arenavirus

Helical capsids contain

RNA-containing granules

Lymphocytic

choriomeningitis

VEE and Lassa Fever

Table 13.2 (18 of 20)



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)



Lentivirus (HIV)

Oncogenic viruses

Use reverse


DNA from viral genome.

Includes all RNA tumor

viruses

Table 13.2 (19 of 20)



Single-Stranded RNA, Two RNA Strands, Produce DNA Lentivirus (HIV)

Oncogenic viruses

Use reverse


DNA from viral genome.

Includes all RNA tumor

viruses

Table 13.2 (19 of 20)



Reovirus (Respiratory

Enteric Orphan)

Rotavirus

Mild respiratory infections

and gastroenteritis

Colorado tick fever

Table 13.2 (20 of 20)



Double-Stranded RNA, Nonenveloped

Reovirus (Respiratory

Enteric Orphan)

Rotavirus

Mild respiratory infections

and gastroenteritis

Colorado tick fever

Table 13.2 (20 of 20)


virus replication


GROWING VIRUSES


Plaques

Cell Culture

Embryonated Eggs


LIFE CYCLE

Parungao-Balolong 2011Thursday, January 26, 2012

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.Thursday, January 26, 2012

VIRUS MULTIPLICATION

Parungao-Balolong 2011Thursday, January 26, 2012

VIRUS MULTIPLICATION (DNA Virus)


• DNA: Cellular enzyme transcribes viral DNA in nucleus


VIRUS MULTIPLICATION : (+ strand RNA Virus)


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.


VIRUS MULTIPLICATION (- strand RNA Virus)



Entryand uncoating




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


VIRUS MULTIPLICATION : (dsRNA Virus)



Entryand uncoating




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


VIRUS MULTIPLICATION (Retrovirus)

Parungao-Balolong 2011• RNA, reverse transcriptase: Viral enzyme copes viral RNA to

make DNA in cytoplasmThursday, January 26, 2012

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Virus structure: classification: replication

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