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KUVEMPU UNIVERSITY Department of P.G. Studies and Research in Applied Botany Jnanasahyadri, Shankaraghatta Shivamogga Dist.577451 Seminar on "Viral Replication" Submitted to: Chairmen Department of Applied Botany, Kuvempu University
Department of P.G. Studies and Research in Applied Botany
Jnanasahyadri, ShankaraghattaShivamogga Dist.577451
Seminar on"Viral Replication"
Submitted by:Gopalkrishna.H.RMSc I semester,Department of Applied Botany,Kuvempu University
Introduction:Replication of virus is very complicated process
Viruses never reproduce by division
They are replicated by a process in which all components of virus are produced separately and are assembled into intact virons.
For replication of virus host is necessary
Visuses are host specific
Host may be a bacteria, plant or an animal
Replication of viruses are studied for first time by experimenting on bacteriophage of the T series [T2, T4 and T6].
There are 2 types of life cycle commonly seen in visuses
They are i] Lytic Cycle ii] Lysogenic Cycle
Lytic and Lysogenic life cycle of virs
Key steps in the Viral Replication Cycle:
AttachmentPenetration (Entry)UncoatingGenome replicationAssemblyMaturationRelease
General steps in in viral replication
Virus are host specific and enters into the host or target cellThis event is electrostatic, does not require any cellular or metabolic energyVirus exhibits cellular tropism
Virus has host range and it may be narrow or broadRabies virus is an example for broad range virusHIV is an example for broad range virusVirusCell typeHIVT lymphocytes, macrophagesRabiesMuscle, neuronsHepatitis A, B, CLiver(hepatocytes)
Virus use receptors and antireceptors for attachment and entry into host cell. Cellular receptors and antireceptors are mostly protein but sometimes they may be glycoprotein, carbohydrates or lipidsThe presence of virus specific receptors is necessaryFor example HIV- CD4 receptor, Rabies-Acetylcholine, phospholpids
2) Penetration [entry]:Penetration is energy dependent process Virus may penetrate into host byEndocytosisTranslocationFusion
3)Uncoating:Refers to the removal or degradation of capsid (uncoating), there by releasing the genome into host cell
The virus genome is transported to the site where transcription/replication can begin
In some there is no degradation of capsid as capsid proteins play a role in viral transcription and replication
4) Genome replication:
Viral genetic material or genome is multiplied within the host
Simultaneously viral structural proteins like capsids are synthesised
Type of genetic material varies from virus to virus
With respect to this all viruses are divided into seven groups by Dr.David Baltimor in 1971
Dr.David Baltimor shared NOBLE PRIZE with Renato Dulbecco, Howard Martin Temin in 1975 for their work on "interaction between tumour viruses and the genetic material of the cell"
Seven groups as follows:Double stranded DNASingle stranded DNADouble stranded RNASingle stranded (+)ve sense RNASingle stranded (-)ve sense RNASingle stranded (+)ve sense RNA with DNA intermediateDouble stranded DNA with RNA intermediate
1.Double stranded DNA:
Example: Poxvirus, Herpes virus
Replication of genome of double stranded DNA virus
Single stranded DNA:
Example: Pircovirus, Parvovirus
Replication of genome of single stranded DNA virus
Double stranded RNA:Example: Reoviruses, Orbibiruses
Replication of genome of double stranded RNA virus
Single stranded (+)ve sense RNA:
Example: Toga virus & Hepatitis E virus
Replication of genome of +sense single stranded RNA virus
Single stranded (-)ve sense RNA:Example: Rabis, Paramyxoviruse etc.
Replication of genome of -sense single stranded RNA virus
Single stranded (+)ve sense RNA with DNA intermediate:
Replication of genome of single stranded (+)ve sense RNA virus with DNA intermediate
Double stranded DNA with RNA intermediate:Example: Hepadnaviruses
Replication of genome of double stranded DNA virus with RNA intermediate
5)Assembly:Involves the collection of all components necessary for formation of vironIt takes place at a particular site in the cellFor example in pox viruses assembly occurs in the cytoplasm; in adenovirus it occurs in nucleus.
Maturation is the stage of life cycle at which the virus become infectious
It involves structural change in virus particles
For some viruses maturation occurs only after release of viurs particle from the cell
Newly formed viruses are released to outside of the cell either by lysis (as in bacteriophage) or by budding(as in paramyxovirus, retrovirus)Generally non enveloped viruses release by cell lysis which results in the death of host cellRelease of virus by budding may or may not kill cell
In general terms, virus replication involves three broad stages carried out by all types of virus; the initiation of infection, replication and expression of the genome, and, finally, release of mature virions from the infected cell. At a detailed level, there are many differences in the replication processes of different viruses which are imposed by the biology of the host cell and the nature of the virus genome. It is possible to derive an overview of virus replication and the common stages which, in one form or another, are followed by all viruses.
Cann, Alan J.. Principles of Molecular Virology, Burlington, MA, USA: Academic Press, (2005)(4th Edition) :page no. 108-129.John B. Carter and Venetia A. Saunders.- Virology-principles and applications, John Wiley & Sons Ltd (2007)Roger Y.Stanier, John L. Ingraham, Mark L.Wheelis, Page R. Painter- General Microbiology, Macmillan Press LTD, (5th edition): page no. 219-228.K.C.Sawant, A Textbook of Virus, Dominant Publishers and Distributors,(2009) (1st Edition) : page no.49-60