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