Viral replication

viral replication
life cycle
types

1. KUVEMPU UNIVERSITY Department of P.G. Studies and Research in Applied Botany Jnanasahyadri , Shankaraghatta Shivamogga Dist. 577451 Seminar on " Viral Replication "   Submitted by : Gopalkrishna.H.R MSc I semester, Department of Applied Botany, Kuvempu University

2. 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

3. Replication of viruses are studied for first time by experimenting on bacteriophage of the T series [T 2 , T 4 and T 6 ]. There are 2 types of life cycle commonly seen in visuses They are i ] Lytic Cycle ii] Lysogenic Cycle

4. Lytic and Lysogenic life cycle of virs

5. Key steps in the Viral Replication Cycle : Attachment Penetration (Entry) Uncoating Genome replication Assembly Maturation Release

6. G eneral steps in in viral replication

7. Attachment: Virus are host specific and enters into the host or target cell This event is electrostatic, does not require any cellular or metabolic energy Virus 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 type HIV T lymphocytes, macrophages Rabies Muscle, neurons Hepatitis A, B, C Liver( hepatocytes )

8. 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 lipids The presence of virus specific receptors is necessary For example HIV- CD4 receptor, Rabies-Acetylcholine, phospholpids

9. 2) Penetration [entry] : Penetration is energy dependent process Virus may penetrate into host by Endocytosis Translocation Fusion

10. 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

11. 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 "

12. Seven groups as follows: Double stranded DNA Single stranded DNA Double stranded RNA Single stranded (+) ve sense RNA Single stranded (-) ve sense RNA Single stranded (+) ve sense RNA with DNA intermediate Double stranded DNA with RNA intermediate

13. 1. Double stranded DNA : Example: Poxvirus , Herpes virus Replication of genome of double stranded DNA virus

14. Single stranded DNA : Example : Pircovirus , Parvovirus Replication of genome of single stranded DNA virus

15. Double stranded RNA : Example: Reoviruses , Orbibiruses Replication of genome of double stranded RNA virus

16. Single stranded (+) ve sense RNA : Example: Toga virus & Hepatitis E virus Replication of genome of +sense single stranded RNA virus

17. Single stranded (-) ve sense RNA : Example : Rabis , Paramyxoviruse etc. Replication of genome of -sense single stranded RNA virus

18. Single stranded (+) ve sense RNA with DNA intermediate: Example: Retrovirus Replication of genome of single stranded (+) ve sense RNA virus with DNA intermediate

19. Double stranded DNA with RNA intermediate: Example: Hepadnaviruses Replication of genome of double stranded DNA virus with RNA intermediate

20. 5) Assembly: Involves the collection of all components necessary for formation of viron It takes place at a particular site in the cell For example in pox viruses assembly occurs in the cytoplasm; in adenovirus it occurs in nucleus.

21. 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

22. 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 cell Release of virus by budding may or may not kill cell

23. 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.

24. 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