Virus Replication Cycle PDF

TOPIC: REPLICATION OF VIRUS SUBMITTED TO: MAM HUMA SUBMITTED BY: SHABANA ASHRAF LAIBA ANDLEEB AIMAN NAZIR MARYAM  TABLE OF CONTENTS 01 02 05 INTRODUCTION TYPES OF LYTIC CYCLE REPLICATIO...

TOPIC: REPLICATION OF VIRUS SUBMITTED TO: MAM HUMA SUBMITTED BY: SHABANA ASHRAF LAIBA ANDLEEB AIMAN NAZIR MARYAM  TABLE OF CONTENTS 01 02 05 INTRODUCTION TYPES OF LYTIC CYCLE REPLICATION 03 04 LYSOGENIC STEPS CYCLE INTRODUCTION Bacteriophage are viruses that specifically infect bacteria, viruses and plant. They need the host cell for replication. Viruses are obligate intracellular parasite. Viruses are host specific. They have a two-phase lifecycle, residing in a dormant state within the host genome (lysogenic cycle) or hijacking the host cellular machinery for their own replication (lytic cycle)  01 LYTIC CYCLE Virus introduces its genome into a host cell and initiates replication by hijacking the host's cellular machinery to make new copies of the virus. Once infection is complete, the newly replicated and assembled virus particles are released through lysis of the host cell into the surrounding STEPS OF LYTIC CYCLE ATTACHMENT ENTRY REPLICATION SELF RELEASE ASSEMBLY STEPS OF LYTIC CYCLE ❑ Attachment: The attachment of the phage takes place to the host cell surface to administer the DNA within the cell. ❑ Entry: The DNA is injected by the phage into the host cell by penetrating the membrane of the cell. Continu….. ❑ Transcription The DNA of the host cell is destructed and the metabolism of the cell is mediated to start the biosynthesis of the phage. ❑ Self assembly: The replication of the phage DNA takes place within the cell, producing novel phage proteins and DNA. Continu… ❑ Release: The newly produce phages are discharged from the infected cell to look out for the novel host cells to infect. Release during the Lytic Life Cycle of a Lytic Bacteriophage. A bacteriophage-coded enzyme breaks down the peptidoglycan in the bacterial cell wall causing osmotic lysis. DIAGRAM 02 lysogenic cycle ❑ A viral genome infect the bacterial or archaeal cell and reproduce along with it , rather than taking control of the host cell and producing new virions. ❑ lysogeny is characterized by integration of the bacteriophage nuclei acid into the host bacterium genome or formation of a circular replicon in the bacterial cytoplasm. ❑ In this condition bacteria continue to live and reproduce. ❑ The genetic material of the bacteriophage called a prophage. STEPS 1-ATTACHMENT 2-PENETRATION 3-INTEGRATION 4-REPLICATION 5-INDUCTION 6-SYNTHESIS 7-ASSEMBLY 8-RELEASE STEPS OF LYSOGENIC CYCLE ❑ Adsorption virus attached to the host cell. ❑ Penetration entry genetic material is injected into the host cell ❑ Integration the phage DNA integrate into the host chromosome forming prophage ❑ Replication the prophage replicate ,viral DNA is copied along with the host cell DNA. each new daughter cell is infected with the virus. CONTINU…. ❑ Induction when the daughter cell is inducted, the viral DNA is excised. ❑ Synthesis The phage DNA and protein are synthesis using the host cell machinery ❑ Assembly The phage DNA and protein are assembled to form new viruses. ❑ Release The virions are released on lysis of the host cell. DIAGRAM DIFFERNCE  03 VIRAL REPLICATION CYCLE 1. Host Cell Requirement: Viruses require a host cell to provide energy and synthetic machinery. 2. Viral Replication Cycle in Host Cell: The viral replication cycle causes dramatic biochemical and structural changes in the host cell, leading to cell damage. 3. Symptoms of Viral Diseases: The symptoms of viral diseases result from the immune response to the virus, attempting to control and eliminate the virus from the body. 4. Viral Release: Many animal viruses, such as HIV, leave infected cells of the immune system through a process called budding REVIEW OF SYMPTOMS ATTACHMENT 4 REPLICATION 1 2 PENETRATION 5 ASSEMBLY 3 UNCOATING 6 RELEASE ATTACHMENT Initial Attachment ▪ Virus particles (virions) attach to specific receptors on the host cell surface ▪ Receptors may be proteins or carbohydrate residues on glycoproteins or glycolipids Specificity of Attachment ▪ Expression of receptors on host cells determines viral tropism ▪ Attachment phase influences viral pathogenesis and infection course Mechanism of Attachment ▪ Initial attachment may be facilitated by cations ▪ Firm binding requires specific receptors on the plasma membrane ▪ Viral surface molecules attach to cellular receptors Examples of Attachment Mechanisms ▪ Orthomyxovirus and paramyxoviruses bind via hemagglutinin ▪ Enteroviruses bind to specific cellular receptor ▪ Multiple viruses may utilize the same receptor PENETRATION 1.Fusion ▪ Enveloped viruses fuse lipid membranes with host cell membrane ▪ Allows viral genome to enter host cell 2. Endocytosis ▪ Viruses taken into cell through host's own membrane ▪ Includes bulk-phase endocytosis and phagocytosis 3. Direct Penetration ▪ Non-enveloped viruses inject genetic material directly into host cell. UNCOATING ▪ Removal of virion's protein coat ▪ Release of genetic material Location of Uncoating ▪ Occurs in the same area as viral transcription ▪ Can occur in the cytoplasm or nucleus REPLICATION Rapid production of viral genome - Relies on type of genetic material the virus possesses Replication Strategies DNA Viruses - Use host cell nucleus replication enzymes - Double-stranded DNA (dsDNA) viruses RNA Viruses - Replicate in cytosol - Directly access host cell's ribosome for viral protein manufacture CONTINU… 1-DsDNA 4-Positive sense RNA 2-SsDNA 5-Negative sense RNA 3-DsRNA 6-RNA& DNA That reverse transcribe Diagram TRANSLATION AND PROTEIN SYNTHESIS ▪ Viruses employ a diverse array of host-directed translational strategies for efficient expression of viral proteins. ▪ Lacking the essential machinery of protein synthesis, for example, ribosomes and other translation factors, all viruses take advantage of the host apparatus to generate virus protein. ▪ Eukaryotic viruses subvert host translation machinery by employing diverse and elaborate RNA-centered strategies, often mimicking host features CONTINU…. ▪ Some viruses have co-opted eukaryotic sequence or structural elements generally employed for condition-dependent regulation, often translation repression. ▪ Viruses can incorporate similar elements to recruit essential constituents of the eukaryote translation apparatus, generally to enhance translation initiation. ▪ Other virus elements recruit host regulatory factors that are not components of the translation machinery. ASSEMBLY ❖ The formation of an immature virus requires the assembly of the capsid, envelopment by a membrane (if enveloped), and packaging of the nucleic acid genome within. ❖ How a particular virus is assembled is dependent on what type of virus it is. ❖ Assembly can occur in the plasma membrane, cytosol, nucleus, Golgi apparatus, and other locations within the host cell. ❖ Some viruses only insert their genome into a capsid once the capsid is completed ❖ In other viruses the will capsid will wrap around the genome as it is being copied. CONTINU…. ❖ Spontaneous assembly of the capsid, termed “self assembly,” occurs with the capsid proteins of simple icosahedral viruses(picornaviruses and parvoviruses). ❖ The assembly of viruses with more complex architecture is orchestrated by a variety of viral chaperone proteins called scaffolding proteins(Herpesviruses and adenoviruses). MATURATION Maturation refers to the final changes within an immature virion that result in an infectious virus particle. Structural Changes occur for the maturation □ proteolytic cleavage □ disulfide bond formation Envelope Acquisition also occurs for maturation □ Envelope protein incorporation □ Lipid bilayer formation Genome Condensation occurs for maturation □ Genome packaging □ Nucleocapsid formation RELEASE ❖ The final step in viral replication is release, which is when the newly assembled and mature viruses leave the host cell. ❖ How a virus releases from the host cell is dependent on the type of virus it is. There are two methods of viral release: lysis or budding. ❖ Lysis results in the death of an infected host cell, these types of viruses are referred to as cytolytic.(e.g. smallpox) ❖ Enveloped viruses are typically released from the host cell by budding ❖ It is this process that results in the acquisition of the viral phospholipid envelope. These types of viruses do not usually kill the infected cell and are termed cytopathic viruses.(Influenza virus)