Virus

Sumit Bohara(BSB)
(Institute of Medicine)
  Study of virus : virology

 Father of virology: W.M Stanley

 Size range: 20-300 nm

Introduction  Smallest plant virus :satellite tobacco

necrosis virus

 Smallest animal virus: foot and mouth virus

of cattle
  Largest and most complex animal virus: pox
virus

 Longest plant virus: citrus tristeza virus

Introduction  Intracellular obligate parasite.

 Connecting link between living and non-living

 Tobacco mosaic was first disease recognized to be

caused by virus.
 1. Presence of genetic materials (DNA or RNA)
2. Host specific
Living properties
3. Undergo Mutation
of virus
4. Contain some enzyme (kill host cell)
5. Can multiply inside host cells
6. Show irritability (character of living beings only)
 1. Can be crystallized
2. No metabolism
3. No energy storing and forming system
Non-living 4. No protoplasm
properties of virus 5. Lack cellular components
6. Cannot multiply outside host cells
Note: living character of virus is the presence of
nucleic acid and non living property is that it can
be crystallized, so virus is called biological puzzle
  By Dmitri Ivanovsky
 First discovered virus (TMV)
 Took Infected tobacco leaf
 He isolate chemical from it
Discovery  Performed experiment on bacteria filter
 Observed Fluid that is still infectious
discovery
 Martinus Beijerinck (1851-1931), a Dutch
microbiologist and botanist, first used the term when
studying the tobacco mosaic virus, becoming
Beijerinck convinced that the virus had a liquid
nature.(contagium vivum fluid)
Louis Pasteur  Gave the term virus.
  First time isolated TMV in crystalline form
W.M. Stanley and showed that crystal were made up of
protein.
Structure of
Virus
  DNA or RNA
 Protein coat (capsid)
Structure  Protein unit (capsomere)
 Envelope
 1. Brick shaped : small pox virus
2. Spherical : influenza virus
3. Rod shaped : TMV
Shape 4. Tadpole like : bacteriophage
5. Bullet shaped : rabies virus
 Capsid Envelope
Protein shell that covers the Outer structure that cover
viral genome the capsid in some viruses
Made up of proteins and
Made up of proteins
phospholipids
Capsid Present in all viruses Present only in some viruses
Encloses the genetic material Encloses the capsid
vs
Capsid shape differs Always spherical in shape
Envelope
Allows the invasion of the
Protects viral genome inside virus into the host cell by
a host cell fusing with the cell
membrane
Protein shell that covers the Outer structure that cover
viral genome the capsid in some viruses
Tobacco
Mosaic Virus
(ss RNA)
Bacteriophage
(ds DNA)
 Plant Phytophage (gen ssRNA)
Animal Zoophage
Algae Phycophage
Virus which Fungi Mycophage
attack Bacteria Bacteriophage (gen dsDNa)
Yeast Zymophage
E.coli Coliphage
  Complete virus particle that consists of an
RNA or DNA core with a protein coat
Virions
sometimes with external envelopes and that is
the extracellular infectious form of a virus.
  Small infectious agent with low molecular
weight
 Naked virus (No protein coat)
 Nucleic acid ss-RNA
Viroids  It caused persistent infection , never
recovered
 Example: potato spindle tuber disease,
cucumber pale fruit, hepatitis D
  The term “prions” refers to abnormal,
pathogenic agents that are transmissible and
are able to induce abnormal folding of
specific normal cellular proteins called prion
proteins that are found most abundantly in
Prion the brain.
1. Contrain protein no nucleic acid
2. Slow virus
3. Exm MCD, Parkinsonism, kuru laughing
disease,
  Protein molecules or polypeptides of low
Interferon molecular weight which prevent viral
multiplication.
Potato Spindle
Tuber Disease
Mad Cow
Disease
Kuru
Laughing
Disease (KLD)
 Lytic cycle (Master and slave relation)

 Phase replicative cycle which causes death of

Bacteriophage host cell.
cycle
 In this phase, virus is virulent and multiplies
in host cell leading to lysis.
  The lysogenic cycle is a method by which a
virus can replicate its DNA using a host cell.
Typically, viruses can undergo two types of
DNA replication: the lysogenic cycle or the
Lysogenic lytic cycle. In the lysogenic cycle, the DNA is
cycle only replicated, not translated into proteins.
 In this phage viral nucleic acid gets
incorporated into host DNA and remain
silent for many generation being replicated
only as the host replicates its own DNA.
Lysogenic
cycle
 Lytic
vs
Lysogenic
cycle
Diseases
  Plant virus (ds DNA)
Classification  Cauliflower mosaic virus
of virus on the  Mirabilis mosaic virus
basis of  Dahlia mosaic virus
genetic
material
  Reosarcoma
 Wound tumor
 Rice dwarf
ds RNA
 Mychophage
 Rota virus
 1. Influenza
2. Rous sarcoma
3. AIDS
4. SARS
5. Rabies
6. Measles
ss RNA 7. Rhino
8. Mumps
9. Yellow fever
10.Dengue
11.All hepatitis except hepatitis b
12.Rubella
13.JE
 1. Adeno virus
2. Hepatitis B
3. HPV
Ds DNA 4. Chickenpox
5. Smallpox
6. Epstein virus
 1. Coliphage s13
Ss DNA 2. Bacteriophage M13
3. Gemini virus