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Title: viruses
Description: You get to know different viruses and the diseases they cause. Also what viruses look like and how they multiply
Description: You get to know different viruses and the diseases they cause. Also what viruses look like and how they multiply
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VIRUSES
Viruses: Are noncellular, non-cytoplasmic or
acellular infectious agents
Virology: The study of viruses
Virologists: Scientists who study viruses
Virus particle (virion): extracellular form of a
virus
THE CONCEPT OF VIRUS
Edward Jenner (1798), introduced the term virus in
microbiology
...
Edward Jenner noticed that milk maids
who
infected with cowpox develop immunity against
smallpox
...
The boy developed sustained immunity against
smallpox
...
They are generally smaller than bacteria, and this can pass
through bacteriological filter
...
Viruses are acellular, non-cytoplasmic infectious agents
...
All viruses are obligate parasites and can multiply only
within the living host cells and are highly resistant to
antimicrobial agents and extremes of physical conditions
...
Viruses do not multiply in chemically defined media
...
Viruses do not undergo binary fission
...
Viruses have a very simple structure
...
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Some circular, but most linear
...
The capsid or protein coat is made up of many identical
protein sub-units called capsomeres
...
GENERAL STRUCTURE AND FUNCTION OF
VIRUSES
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...
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...
Thus, viruses
show characters of both living and non-living
...
Some viruses have additional lipoprotein envelope ,
composed of virally coded protein and host lipid
...
Some viruses have enzymes inside the virion
...
Non-living Characters of Viruses:
Following characters of viruses assign them as non-living:
(a) They can be crystallized
...
(c) They do not show growth, development, nutrition,
reproduction, etc
...
Living characters of viruses:
(a) They multiply within host cells
...
(c) There are definite races or strains
...
(e) Lack enzymes for most metabolic processes
...
Because of the above reasons, viruses form unique bridge
between living and non-living things
...
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...
Helical, enveloped
•Envelopes form when viral
glycoproteins and oligosaccharides
associate with the plasma
membrane of the host cell
...
3
...
Polyhedral (Icosahedral), enveloped
Polyhedral means many sides (most are
icosahedral - 20 triangular faces and
12 corners)
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...
Bacterial viruses contain
complicated structures, icosahedral heads and helical tails
...
This group comprises all those viruses which do not fit into
either of the above two groups
...
Common names are used for species
Subspecies are designated by a
number
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CLASSIFICATION OF VIRUSES
(1) Nucleic acid type: RNA or DNA; single-stranded or doublestranded; strategy of replication
...
(3) Presence of specific enzymes, particularly RNA and DNA
polymerases, and neuraminidase
(4) Susceptibility to physical and chemical agents, especially
ether
...
(6) Natural methods of transmission
...
(8) Pathology; inclusion body formation
...
VIRUS CLASSIFICATION
DNA VIRUSES
PARVOVIRIDAE
POLYOMAVIRIDAE
ADENOVIRIDAE
HERPESVIRIDAE
HEPADNAVIRIDAE
POXVIRIDAE
RNA VIRUSES
TOGAVIRIDAE
FLAVIVIRIDAE
BUNYAVIRIDAE
PICORNAVIRIDAE
REOVIRIDAE
RHABDOVIRIDAE
ARENAVIRIDAE
CORONAVIRIDAE
PARAMYXOVIRIDAE
ORTHOMYXOVIRIDAE
RETROVIRIDAE
VIRAL REPLICATION
•
•
•
A bacteriophage (informally, phage) is a
virus that infects and replicates within a
bacterium
...
Animal virus infections can be either lytic or
lysogenic
...
5 STEPS OF LYTIC
CYCLE
Attachment to the cell
2
...
Replication (Biosynthesis) of new
viral proteins and nucleic acids
4
...
Release of the new viruses into the
environment (cell lyses)
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BACTERIOPHAGE REPLICATION
Bacteriophage
inject their
nucleic acid
They lyse
(break open) the
bacterial cell
when replication
is finished
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LYTIC CYCLE REVIEW
Attachment
Penetration
Biosynthesis
Maturation
Release
Phage attaches by tail fibers to
host cell
Phage lysozyme opens cell wall,
tail sheath contracts to
force tail core and DNA into
cell
Production of phage DNA
and proteins
Assembly of phage particles
Phage lysozyme breaks cell wall
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Bacterial
cell wall
Bacterial
chromosome
Capsid
DNA
Capsid
Sheath
1
Attachment:
Phage
attaches to
host cell
...
Sheath
contracted
Tail core
3
Merozoites
released into
bloodsteam from
liver may infect
new red blood
cells
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Tail
4
5
Maturation:
Viral components
are assembled into
virions
...
DNA
Capsid
Tail fibers
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LYSOGENIC CYCLE
Phage
DNA injected
into host cell
Viral DNA joins host
DNA forming a
prophage
When
an activation
signal occurs, the
phage DNA starts
replicating
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LYSOGENIC CYCLE
Viral
DNA (part of
prophage) may stay
inactive in host cell for
long periods of time
Replicated during each
binary fission
Over time, many cells
form containing the
prophages
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THE LYSOGENIC CYCLE
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LYTIC AND LYSOGENIC
CYCLES
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Title: viruses
Description: You get to know different viruses and the diseases they cause. Also what viruses look like and how they multiply
Description: You get to know different viruses and the diseases they cause. Also what viruses look like and how they multiply