KUVEMPU UNIVERSITYDepartment of P.G. Studies and Research in

Applied BotanyJnanasahyadri, Shankaraghatta

Shivamogga Dist.577451

Seminar on"Viral Replication"

 

Submitted by:Gopalkrishna.H.R

MSc 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:

1. Attachment2. Penetration (Entry)3. Uncoating4. Genome replication5. Assembly6. Maturation7. Release

General steps in in viral replication

1. Attachment: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 broad Rabies virus is an example for broad range virus HIV is an example for broad range virus

Virus Cell typeHIV T lymphocytes,

macrophagesRabies Muscle, neuronsHepatitis A, B, C Liver(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 by

1. Endocytosis2. Translocation3. Fusion

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:

I. Double stranded DNAII. Single stranded DNAIII. Double stranded RNAIV. Single stranded (+)ve sense RNAV. Single stranded (-)ve sense RNAVI. Single stranded (+)ve sense RNA

with DNA intermediateVII. Double stranded DNA with RNA

intermediate

1.Double stranded DNA:

Example: Poxvirus, Herpes virus

Replication of genome of double stranded DNA virus

II. Single stranded DNA:

Example: Pircovirus, Parvovirus

Replication of genome of single stranded DNA virus

III. Double stranded RNA:

Example: Reoviruses, Orbibiruses

Replication of genome of double stranded RNA virus

IV. Single stranded (+)ve sense RNA:

Example: Toga virus & Hepatitis E virus Replication of genome of +sense single stranded RNA virus

V. Single stranded (-)ve sense RNA:

Example: Rabis, Paramyxoviruse etc.

Replication of genome of -sense single stranded RNA virus

vi. Single stranded (+)ve sense RNA with DNA intermediate:

Example: Retrovirus

Replication of genome of single stranded (+)ve sense RNA virus with DNA intermediate

VII. 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.

6) Maturation:

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

7) Release: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

Conclusion:

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.

Bibliography: 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

  http://www.columbia.edu/itc/hs/medical/pathophys/id/2004/lecture/notes/

viral_rep_Hammer.pdf https://en.wikipedia.org/w/index.php?

title=Special:Book&bookcmd=rendering&return_to=Viral+replication&collection_id=1b11e82521fac6c63fdacbbdc6faa2a

http://www2.oakland.edu/biology/chaudhry/pics/virusreplication02web.pdf