Virus (poisonous fluid)
Virus: Connecting link between living(inside the host) and non-living(outside the host).
*Term given by Louis Pasteur.
*Acellular organism (lack protoplasm).
Non-living like feature:
*Lack functional autonomy -central dogma.
*High specific gravity.
*Can be crystallize.
*Doesn't reproduce outside the host.
Living organism like feature:
*Made up of biomolecule(protein +nucleic acid).Hence called proteinaceous particle.
*Possess enzyme.
*Reproduce inside the host.
*Host specificity.
*Cause diseases in host.
*Possess genetic material.
*Can undergo mutation.
Discovery of Virus:
*D.J. Iwanowosky- Discovered the virus as causal organism of Tobacco Mosaic Virus that can pass through bacterial proof filter .
*W.M. Beijernick - Proposed the theory of "Contagium vivum fluid" .Living infectious fluid.
*W.M.Stanley - Crystallisation of TMV. Reported that viruses are largely made up of proteins .
Structure of Virus:
Capsid +Nucleoid
1)Envelope -outermost covering found only in some animal viruses.Example- Herpes Virus.Its unit called peplomere made up of protein +carbohydrate+ fats.Protein is of viral origin and carbohydrate is of host origin.
2)Capsid- Outer proteinaceous covering found in all viruses.Unit-capsomere,protective.
3)Nucleoid or Genetic Material-
Either DNA or RNA.
None of the viruses possess both DNA as well as RNA.
Responsible for disease in host.
Classification Of Viruses:
on basis of genetic material
1)Deoxyriboviruses: Genetic material is DNA.These viruses either have ssDNA (M13phage, coliphage)or dsDNA(Herpes virus,Poz virus,CMV-Cauliflower Mosaic Virus)
2Riboviruses: Gebetic material is RNA. These viruses either have ssRNA (TMV,HIV,Reovirus) or dsRNA(Wound tumour virus)
On basis of host by Homes
1)Phaginae: parasitic on lower organisms. Example-Bacteriophage(on bacteria), Mycophage(on fungi),Cyanophage(on cyanobacteria)
2)Phytophaginae: parasitic on palnts.Genetic material is generally ssRNA exception CMV(dsDNA).
3)Zoophaginae: parasitic on animals.Genetic material may be ssRNA,dsRNA,dsDNA.None of the animal virus possess ssDNA as genetic material.
Structure of TMV:
Rod shaped virus.
Capsid -capsomeres =2130
Genetic material is ssRNA ,nucleotide is nearly 6400.
Ratio- Capsomere :Nucleotide
1 : 3
Steucture of T2 bacteriophage:
Polyhedral virus.
It have three parts:
1)Head
2)Neck-further have collar and neck.
3)Tail
Genetic material is dsDNA
Reproduction in Virus:
Occurs only inside the host.
Two type of life cycle of virus.
1)Pinocytic virus: When whole virus enters inside the host.Example-HIV,TMV,Polio virus.
2)Phagic cycle: When only genetic material of the virus enters in the host.Example-T2 bacteriophage,T4 bacteriophage(virulent show lytic cycle),Lambda phase(non-virulent show lysogenic cycle).
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