Viral Replication PDF

VIRAL REPLICATION  OVERVIEW Introduction Steps in viral replication(Recap) Types of viral replication Similarities between types of viral replication Difference between types of viral replication  INTRODUCTION Virus replication: is a pr...

VIRAL REPLICATION  OVERVIEW Introduction Steps in viral replication(Recap) Types of viral replication Similarities between types of viral replication Difference between types of viral replication  INTRODUCTION Virus replication: is a process by which viruses creates new infectious copies of themselves inside a host cell. Viruses can only replicate inside the living cells of organism and they lack ability to carry out metabolic processes or reproduce independently  STEPS IN VIRAL REPLICATION Virus infect cells through a multstep process which involve the following stages ❖Atachment and entry ❖Uncoating ❖Replication and transcription ❖Assembly ❖Release  ATTACHMENT AND ENTRY Virus target specific receptors on the surface of host cells allowing them to attach with precission Then virus enters the host cell through various mechanism such as endocytosis,direct fuse whith the membrane and release genetic material or Attach on cellsurface receptors and injecting its genetic material into the cell When virus inject its DNA the empty coat remain outside the cell  UNCOATING Viral which enters the cell by endocytosis sheds its outer coat(capsid) releasing its genetic material into the cytoplasm This step is essential for the genome to be accessible for replication and transcription  REPLICATION AND TRANSCRIPTION The viral DNA is often transported to nucleus where it hijacks the host cell machinery and being replicated using the hosts polymerases For RNA viruses they may replicate in the cytoplasm,where viral RNA dependent RNApolymerase synthesises new viral RNA genomes  ASSEMBLY New synthesized viral components come together to form complete viral particles within the hosts cell This can occur in the cytoplasm or nucleus depending on the virus type(DNA viruses or RNA viruses)  RELEASE Once assembled the newly formed viruses are released from the host cell to infect other cells continuing the cycle of infection This can occur either through lysis(causing cell death),waiting for the cell to die or by budding off through the cell membrane  INCUBATION PERIOD Is a time from when a virus infect an organism to when virus makes so many copies that organism start to react. Example Influenza is (1-4)days ,Corona virus has incubation period of up to 14 days It is asymptomatic period and one can not recognize weather he or she is sick  TYPES OF VIRAL REPLICATION ❖LYTIC REPLICATION ❖LYSOGENIC REPLICATION  LYTIC REPLICATION (active phase) The virus hijacks the hosts cell machinery to produce new viral particles rapidly Viral takes over all metabolic activities of a cell replicating itself many times and then destroy host cell Host cell burst releasing a multitude of newly formed viruses It is characterized by its rapid onset often leading to the distruction of host cell and spread of the virus into neighbouring cells  LYSOGENIC REPLICATION (dormant phase) In lysogenic replication, After viral inject its DNA into the host cell ,DNA intergrates into the host cell genome lying dormant as a prophage and is being called PROVIRUS Viral nucleic acid become part of the host cell chromosome and is replicated with it during host cell reproduction(long silence) At this time Provirus is inactive when the cell divided both host gene and viral gene are passed to the daughter cells  LYSOGENIC REPLICATION Under specific triggers (such as various stresses causing DNA damage,chemical stimulus,temperature variation) provirus may leave the host chromosome and enters lytic cycle. when this happen host cell DNA is brocken down and new viruses are produced in a cell leading to cell rupture and release new viruses Lysogenic replication allow the viral to persist within the host cell for extended periods potentially spreading its genetic material to subsequent generations of host cells  LYSOGENIC REPLICATION Sometimes a viral will invade DNA of a cell and then it loses its viral ability over generations of cell replication Virus can mutate(forget how to be a virus) and just live as junk DNA inside a cell Example Helpes Simplex Virus---It finally lead to painfull blisters due to shifting from silence/dormant phase(lysogenic) to lytic phase(blisters) SIMILARITIES BETWEEN LYTIC AND LYSOGENIC LIFE CYCLE Both initiated by the binding of the virus to a host cell receptor molecule. Both require cellular machinery of the host cell. Both have capacity to produce several viral particles from a single one that infected the host cell. NB:The key differences between LYTIC and LYSOGENIC viral replication are ❖CELL FATE: Lytic leads to immediate cell death while lysogenic allows the host cell to survive initially ❖VIRUS PRODUCTION : Lytic produces viruses immediately, lysogenic can delay viral production for a time Other more differences are described below  REFERENCE ❖Alberts,B.,Johnson,a.,Lewis,J.,Raff,M.,Roberts,K.,&Walter,P(2014).Molecular biology of the cell(6 edition).Garland science ❖Carter,J.,& Saunders,V.(2007).Virology:Principles And Application.Wiley. ❖Flint, S. J., Enquist, L. W., Krug, R. M., & Racaniello, V. R. (2015). Principles of Virology (4th ed.). ASM Press. ❖Whittaker, G. A., & Leary, J. R. T. P. (2015). Virus Structure and Assembly. Wiley. ❖Salyers, A. A., & Whitt, D. D. (2005). Bacterial Pathogenesis: A Molecular Approach (2nd ed.). ASM Press. ❖Tortora, G. J., Funke, B. R., & Case, C. L. (2016). Microbiology (12th ed.). Pearson. ❖Harper, D. R., & McLellan, S. J. (2014). Viral Pathogenesis. Springer. ❖Meyer, K. H. F. (2012). The Biology of Viruses. Springer