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VIRUSES ,VIROIDS & LICHENS DETAILED INFORMATION

VIRUSES

Viruses are non- cellular , npn- living infectious agents that are composed of nucleo­pro­teins which can multiply inside animals and plants or bacterial cells.It consists of both living and non- living properties
LIVING­_PR­OPE­RTIES OF VIRSUES
NON_ LIVING PROPERTIES OF VIRUSES
]1)They are obligate intrac­ellular parasi­ties,
1)They can be crysta­llized and stored in bottles
i.e<,c­annot exists outside .
 
2)They can multiply inside the living organisms
2)They cannot multiply outside the host
3)They contain a genetic material namely DNA or RNA
3)They dont have the cells
SIZE:- Virsues range in size from 300 nanometers as in TMV to 20nm as in parvov­iruses.
viruses approx­imate the sizes of the smallest bacterial cells as mycopl­asmas.
largest viruses is vaccinia virus and pox virus,
smallest viruses is foot and mouth disease virus,­polio virus

SHAPE

Spherical
polio virus
rod shaped
TMV virus,­inf­luenza virus
rectan­gular
vaccinia virus
polyhedral
adeno virus, herpes virus,­polio virus
tadpole shaped
bacter­iop­hages
Helical
Rabies virus , TMV
classi­fic­ation of viruses
phytop­hages viruses that infect plants
zoophages viruses that infect animals
bacter­iop­hages viruses that infect bacteria
cyanop­hages viruses that infect blue green algae
zymophages viruses that infect yeast cells
mycophages viruses that infect fungi

NUCELIC ACID

Generally plant virus consists of RNA but in caulif­lower mosaic virus and dahila mosaic virusthe genetic material is double standard DNA
Generally animal virus consists of DNA but in polio virus,flue virus it is single standard RNA
A single standard DNA is present in bacter­iophage M14 and coliphage S13
A double standard RNA is present in Wound tumor virus ,Rice dwarf virus, Maize dwarf virus, Reo virus

CAPSID

1) Chemically viruses contain a protein coat called capsid.The capsid consists of many protein subunits called capsomere. The number of capsomere varies from one virus to another virus
eg:- TMV capsid contains 2130 capsom­eres.
Adeno virus contains 252 capsom­eres.

2) Some animal viruses like influenza virus and AIDS contain aalipi­d-p­rotein complex external to capsid. this is called peplos or envelope.
The capsomeres in capsid may be arranged in helically (eg:-TMV ) polyhedral (eg:- adeno virus) and binal symmertry (eg:- TMV)

DIFFERENT TYPES OF VIRUSES

TMV VIRUS
BACTER­IOPHAGE
POX VIRUS
AIDS VIRUS
TMV is most extens­ively studied plant virus.
They are pathogenic virus infecting bacteria
POX virus is aa casual agent of small pox.
Acquired immune deficiency syndrome(AIDS)is an infectious diseases is caused by a virus known as human immuno­def­iciency virus (HIV)
It is elongated rod-li­ke,­3000A0long ,180A0 in diameter, molecular weight being 39.4*106, 95%protein and 5% RNA by weight interwined to form helical ,groov­ed,­cyl­ind­erical rods.
Twort discovered the bacter­iop­hages. The structure of T4 bacter­iophage contains head and tail regions.
pox virus are among the largest of animal virus ,have complex structure and rectan­gular shaped
This virus also called as Human T lympho­tropic virus 3 or AIDS related retrovirus (ARV)
The walls of the cylinder are 70A0 thick.2130 capsomers are arranged helically to form aa capsid .
Head is folded double standard DNA is packed in head.Head is hexagonal with around 2000 capsom­eres.
This is rectan­gular shaped (300*2­30mU) in size ,6% double standard DNA ,89% protein ,5% lipids.
AIDS virus consists of single standard RNA surrounded by protein coat( core shell) the entire structure is wrapped around in an envelope.
49 capsomers are present in 3 turns and 130 turns in complete virus capsid. Each capsomere has a molecular weight of 17,400 and is formed by conden­sation of 158 aminoacids
Tail is helically symmet­rical with a core tube surrounded by a protein tail sheath consists of 144 capsomeres arranged in 24 rings of 6 subunits. The sheath is connected to collar at its upper end and base plate at lower end.
Genome is dumb bell shaped­;ce­ntral core has dsDNA.
After entering the blood, AIDS virus infects the helper T-LYMP­HOC­YTE­S(not the suppressor T-cells) and destroy them. Helper T cell plays an essential role in antibody produc­tion.
RNA strand is embeddedin furrow and theref­ore,it is helica­l;ssRNA consists of 6400 nucleo­tid­es.Thus , the approx­imate ratio of nucleo­tides and capsomers is 3:1
basal plate is hexagonal with single pin or spike at each corner. A thin tail fibre is also given out of the corner . A enzyme lysozyme is respon­sible for dissolving the bacterial cell wall is present in tail fibers.
The core contains two enzymes - RNA polymerase and **ATP-­pho­sph­ohy­dra­lase.On both sides of the core lie lateral bodies one on each side.
Thus, AIDS virus destroy an important link in immune defence rendering the indivi­duals prone to infectious diseases and tumour formation.

VIRIODS

DIENER discovered the viroids .They are small, circular, single standard RNA molecules without protein coat . they cause many plant diseases .
Eg:- Citrus exocotosis viroid , potato spindle tuber viroid

Although the viroid RNA (300 to 400) nucleo­tides is single standard circle but can exhibit consid­erable secondary structure and resembles the short standard molecules with close ends.
viroids enter the plant through wound or by insects. It replicates in the host cell nucleus with the help of one plant of RNA polyme­rases.

PRIONS

PRUSINER discovered the prions. The infectious proteins are called prions. Nucleic acid is absent. Protein coat is infectious and cause variety of diseases. The mad cow disease causing prion may reach man through beef cause Creutz­fel­dt-­Jakob diseasein him. eg:- MAD COW disease (Bovine spongiform enceph­alitis) and Scrapie disease in sheep.
                               
 

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