Chair of Medical Biology, Microbiology, Virology, and Immunology
MORPHOLOGY AND PHYSIOLOGY OF
VIRUSES
Lecturer As. Prof. Olena V.Pokryshko
3000BC
a noncellular small obligate intracellular parasites (genetic element)
contains either a RNA or DNA genome surrounded by a protective, virus-coded protein coat
has no its own biosynthetic machinery for energy generation and protein synthesis
For propagation virus depends on specialized host cells
infects a cell for its own replication, it has an extracellular state.
Virus:
A virus particle containing nucleic acid surrounded by protein and other macromolecular components is called virion.
Viruses have a heavy dependence on host-cell structural and metabolic components.
Viruses can confer important new properties on their host cell.
Viruses may be non productive, latent, oncogenic, chronic or lytic.
Virus:
The main purpose of a virus is to deliver its genome into the host cell to allow its expression (transcription and translation) by the host cell.
Methods of Analysis
Filtration Through Membranes of Graded Porosity
Sedimentation in the Ultracentrifuge
Direct Observation in the Electron Microscope
The resolution is 5nm (1nm = 10-9 m)
Ionizing Radiation
X-ray crystallography
Size of Viruses
A small virus has a diameter of about 20nm.
Parvovirus
A large virus has a diameter of up to 400nm.
Poxviruses
Shape of Viruses Spherical Rod-shaped Brick-shaped Tadpole-shaped Bullet-shaped Filament
Shapes of VirusesShapes of Viruses:Spherical:Spherical
Shapes of Viruses :Rod-shaped
Shapes of Viruses :Brick-shaped .
Tadpole-shapedTadpole-shaped
Shapes of Viruses :Bullet-shaped
Shapes of Viruses :Filament
Some viruses infected human body
Viruses
Viral StructureViral Structure
All viruses have two parts a nucleic acid core a protein coat called a capsid.
Viral StructureViral Structure
envelope Viruses without an envelope are known as naked
viruses
Packaging or condensation of nucleic acid
Protection of nucleic acid
Transport nucleic acid from cell to cell
Provides specificity for attachment
Capsid functions
Functions of envelope
Antigenicity
some viruses possess neuraminidase Infectivity Resistance
Virus Specific Enzymes
Some viruses have enzymes for Penetration of the host cell
ex. Haemagglutinin, Neuraminidase, bacteriophages have Lysozyme for penetration of bacterial cell walls
Replication of viral nucleic acid ex. Retroviruses carry Reverse transcriptase
Nucleic acids (1-40 %) Proteins (70-90 %) Lipids (15-35 %) Glycolipids Glycoproteins
Chemical composition of viruses
Viral proteins (70-90 %): structural (capside, envelope, matrix, core, associated with nucleic acid) non-structural
Structural proteins are in virion in its extracellular state. Functions: protection of nucleic acid, interaction with the membrane of susceptible cell provide viral penetration into the cell, have RNA- and DNA-polymerase activity etc.
Non-structural proteins are absent in virion in its extracellular state, but they are formed during viral reproduction Functions: provide regulation of viral genome expression, are viral precursor proteins and can inhibit cell biosynthesis.
Lipids (15-35 %) are in enveloped viruses in their envelope
Functions: Stabilization of viral shell, Protection of inner virion shells and nucleic acid, Deproteinization of virions
Carbohydrates molecules are in glycoproteins and glycolipids (3,5-9 %).
They protect these molecules from cell proteases action
How Viruses are classifiedMain criteria presently used are:
Acid type.
Size and morphology, including type of symmetry, number of capsomeres, and presence of membranes.
Presence of specific enzymes, particularly RNA and DNA polymerases, and neuraminidase
Susceptibility to physical and chemical agents, especially ether.
Immunologic properties.
Natural methods of transmission.
Host, tissue, and cell tropisms.
Pathology; inclusion body formation.
Symptomatology.
Viral ClassificationViral Classification
1. By the type of nucleic acid RNA or DNA; single-stranded or double-stranded; strategy of replication
DNA-Containing Viruses
RNA-Containing Viruses
Hepadnaviridae Picornaviridae Paramyxoviruses
Parvoviridae Caliciviridae Orthomyxoviruses
Papovaviridae Togaviruses Bunyaviridae
Adenoviridae Flaviviridae Arenaviridae
Herpesviridae Coronaviridae Reoviridae
Poxviridae Rhabdoviridae Birnaviridae
Iridovoridae Filoviridae Retroviridae
Viral ClassificationViral Classification
2. By what type of outer covering they have
capsid - naked (simple) envelope - complex
Naked viruses( Non Enveloped )Naked viruses( Non Enveloped ) Adeno-associated Virus (AAV)
AdenovirusCoxsackievirus - ACoxsackievirus - BEchovirusHepatitis A Virus (HAV)Hepatitis E Virus (HEV)Norwalk Virus
Enveloped virusesEnveloped viruses California Encephalitis Virus Coronavirus Eastern Equine Encephalitis Virus
(EEEV) Epstein-Barr Virus (EBV) Hepatitis B Virus (HBV) Hepatitis C Virus (HCV) Hepatitis Delta Virus (HDV) Rotavirus Rubella Virus Saint Louis Encephalitis Virus Smallpox Virus (Variola) Vaccinia Virus
Herpes Simplex Virus 1 (HHV1) Herpes Simplex Virus 2 (HHV2) Cytomegalovirus (CMV) Human Immunodeficiency Virus
(HIV) Human T-lymphotrophic Virus
(HTLV) Influenza Virus (Flu Virus) Varicella-Zoster Virus (HHV3) Venezuelan Equine Encephal. Vir.
(VEEV) Western Equine Encephalitis Virus
(WEEV) Yellow Fever Virus
3. By the shape (symmetry) of the virus3. By the shape (symmetry) of the virusDetermined by its capsid
Icosahedral (cubic) Helical Complex
Viral ClassificationViral Classification
Helical Capsid In the replication of viruses with helical symmetry, identical protein subunits (protomers) self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path. Such nucleocapsids form rigid, highly elongated rods or flexible filaments
Tobacco mosaic diseases virus
Helical SymmetryHelical SymmetryCalifornia Encephalitis VirusCoronavirusHantavirusInfluenza Virus (Flu Virus)Measles Virus ( Rubeola)Mumps VirusParainfluenza VirusRabies VirusRespiratory Syncytial Virus(RSV)
Icosahedral CapsidIcosahedral Capsid A polyhedron with 20
equilateral faces and 12 vertices
capsomers ring or knob-shaped units
made of 5 or 6 protomers pentamers (pentons) – 5
subunit capsomers hexamers (hexons) – 6
subunit capsomers
IcosahedralIcosahedral Adeno-associated Virus
(AAV)AdenovirusB19Coxsackievirus - ACoxsackievirus - BCytomegalovirus (CMV)Eastern Equine Encephalitis Virus (EEEV)EchovirusEpstein-Barr Virus (EBV)Hepatitis A Virus (HAV)Hepatitis B Virus (HBV)Hepatitis C Virus (HCV)Hepatitis Delta Virus (HDV)Hepatitis E Virus (HEV)
Herpes Simplex Virus 1 (HHV1)Herpes Simplex Virus 2 (HHV2)Human Immunodeficiency Virus (HIV)Human T-lymphotrophic Virus (HTLV)Norwalk VirusPapilloma Virus (HPV)Polio virusRhinovirusRubella VirusSaint Louis Encephalitis VirusVaricella-Zoster Virus (HHV3)Western Equine Encephalitis Virus (WEEV)Yellow Fever Virus
Capsid symmetryCapsid symmetry
Icosahedral Helical
Naked capsid
Enveloped
Lipid
Glycoprotein
Matrix
Complex SymmetryComplex Symmetry
many viruses do not fit into helical or icosahedral symmetry Examples: poxviruses and large bacteriophages
Vaccinia virus
200x400x250 nm, enveloped virus DNAWith double membrane envelope.
T4 phage
Binal symetry: head icosahedron, tail helical.Tail fibers and sheath used for binding and pins for injecting genome
Viral ClassificationViral Classification4. by who they infect
Host Cell Specificity Very specific--Three levels
1.
2.
3.
Viral ClassificationViral Classification5. By how they infect
DNA viruses joins with host’s DNA (goes) to RNA
RNA viruses (goes) straight to protein with use of host’s ribosomes (in the
cytoplasm)
Retroviruses use enzyme reverse transcriptase
converts viral RNA to DNA
and new DNA can become
part of host DNA or go to RNA
Classification of Viruses
By symptomatology - oldest By routes of transmission Plant, animal or bacterial
Classification by SymptomatologyClassification by Symptomatology
Dermatotropic - lesions of skin and mucous membranes
cold sores, shingles, warts
Pneumotropic flue, parainfluenza, respiratory syncytial viral pneumonia,
Neurotropic - CNS encephalitis
Viscerotropic - organs hepatitis, infectious parotitis
Generalized
Classification According to Routes of Transmission Respiratory transmission
Influenza A virus Faecal-oral transmission
Enterovirus Blood-borne transmission
Hepatitis B virus Sexual Transmission
HIV Animal or insect vectors
Rabies virus, Western equine encephalitis, yellow fever, West Nile fever, dengue fever
Life cycle of a virusLife cycle of a virus
Process of virus replication1. Lysogenic Cycle
2. Lytic cycle
Viral ReplicationViral Replication11. . AttachmentAttachment
Virus comes in contact with Virus comes in contact with receptor sitesreceptor sites on on surface of host cell (specific host cell)surface of host cell (specific host cell) Virus attaches to cell Virus attaches to cell
Attachment of viruses
Chemical attraction
Have glycoprotein spikes or other attachment molecules that mediate attachment
Viral ReplicationViral Replication 22.. Penetration
Enveloped viruses join with cell membrane
Penetration of animal viruses occur
by direct penetration (a),
fusion (b) between the viral envelope and the the host cell
membrane or endocytosis (c) - clathrin-coated pits
Viral ReplicationViral Replication22.. Penetration
Viral ReplicationViral Replication22. . Inject DNAInject DNA
Inject DNA Naked virus injects nucleic acid into host
Viral ReplicationViral Replication33. . Uncoating and ReplicationUncoating and Replication
Viral DNA (or RNA) directs protein synthesis Viral nucleic acid causes host cell to produce parts of
virus
Viral Replication4.4. AssemblyAssembly
Nucleic acid are inserted into capsid New viruses are ready to be released
Viral Reproduction5.5. ReleaseRelease
Host cell membrane breaks down Viruses are released
LYTIC CYCLE
Viral ReproductionReleaseRelease Enveloped viruses move through cell membrane,
taking some of the cell’s membrane with it
Viral release from cell
Cell lysis, “burst”
Simple viruses
Budding
Enveloped viruses
> 4000 (poxviruses)> 4000 (poxviruses) - - >100>100 000 000 ((polyovirusepolyoviruse))
Virus replication: generalVirus replication: general
From Schaechter’s Mechanisms of Microbial Disease; 4th ed.; Engleberg, DiRita & Dermody; Lippincott, Williams & Wilkins; 2007; Fig. 31-7
Variations on the replication theme
Types of viral infection
ProductiveАbortive
Virogeny
Viruses caused the virogeny are temperately ones
Cultivation of virusesCultivation of viruses
Tissues cultures
Chick embryos
Laboratory animalsBacteria (for bacteriophages)
The early developing bird embryo contains a protective case, providing an ideal environment for viral propagation.
POCKS on Chorio-Allantoic POCKS on Chorio-Allantoic Membrane of Chick Embryo: Membrane of Chick Embryo: Vaccinia virus (left) HSV-1 (right)Vaccinia virus (left) HSV-1 (right)
IntracerebrallyIntracerebrallyIntraperitoneallyIntraperitoneallyIntramuscularlyIntramuscularlyIntravenouslyIntravenouslyIntranasallyIntranasally
Inoculation of laboratory animal
Types of cell cultureTypes of cell culture
Primary
Diploid Continuous
1949 - Enders, Weller, & Robinson - grow polio in non-neural cellsCells can grow as monolayers or in suspension cultures: glass (in vitro) and plastic
Tissue CulturePrimary cell lines are derived directly from tissue after treatment with
trypsin. Die after a few generations - Limited to 5-20 cell divisionsFibroblasts of human embryo, Rhesus monkey kidney, Chiken fibroblasts
Continuous cell lines - immortal cells derived from tumors or mutagenesis of primary cells. HeLa (Henrietta Lacks), HEp-2 (Hu. Epithelial), BHK (Baby Hamster Kidney), Detroit-6.Disadvantages: May not resemble the original cell of origin Less differentiated - lost morphological and biochemical features Can be tumorigenic
Diploid cell lines - homogeneous population of a single type (fibroblast-liked cell). Typically derived from tumors. Can divide up to 100 times. Remain diploid
WI-38, MRC-5, MRC-9, IMR-90
Cell culture obtaining
CPE:Viral Cytopathological Effects Cell death
Cell rounding/Degeneration/Aggregation
Lass of attachments to substrate Inclusion bodies in the nucleus or cytoplasm, margination of
chromatin Syncytia: multinucleated giant cells caused by virus-induced
cell-cell fusion Cell surface changes
Viral antigen expression
Hemadsorption (hemagglutinin expression)
Normal cell and CPENormal cell and CPE
InclusionsInclusions
Negri body
Large cells with typical nuclear “owl’s eye” inclusions
Formation of syncytia
Giant multynucleated skin cells (simple herpes virus)
Hemadsorption
Morphologic transformation by an oncogenic virus
Normal cells Infected cells
Major viral disease treatment Major viral disease treatment factoids:factoids:
No viral disease has ever been CURED by medical treatment.
Viruses are not susceptible to ANTIBIOTICS. If a doctor tells you he/she is treating your VIRUS INFECTION with an antibiotic, he/she is either stupid or lying and you should seek more competent medical advice.
The most effective tool is prevention (immunization)
Thanks