Virus GN.pdf

Viruses Biomedical science Benjamin Tighe  Intended Learning Outcomes By the end of this sessions students should be able to: Be familiar with the structure and classification of viruses Outline the features of HIV, hepatitis B virus, varicella zoster virus, herpes. and inf...

Viruses Biomedical science Benjamin Tighe  Intended Learning Outcomes By the end of this sessions students should be able to: Be familiar with the structure and classification of viruses Outline the features of HIV, hepatitis B virus, varicella zoster virus, herpes. and influenza viruses according to their symmetry and nucleic classification. Identify dentally relevant viruses and link with their disease. Understand the concept of viral tropism. Outline how viruses replicate and spread within the host. Explain the terms viral persistence & viral latency Explain the structural features and relevance of prions  Smaller than Bacteria. Obligatine intracellular parasites. have the ability to Features of a virus don't infect themselves so have to infect a - host cell. An infectious particle that reproduces by "commandeering" a host cell and using its machinery to make more viruses. Made up of a DNA or RNA genome inside a protein shell called a capsid. Loading… Some viruses have an external membrane envelope. Come in different shapes and structures, have different kinds of genomes, and infect different hosts. Viruses reproduce by infecting their host cells and reprogramming them to become virus-making "factories."  Genome DNAOR ! RNA-not both ↓ ↓ DNA virus RN J ↓ linea Single RNA Stranded DNA  Morphological Similar subunits capsomeres made of a number of capsomenes protein cost arranged precisely. - Genome each capsomene is composed of protomenes. and in pattern to complete form a capsid. Capsid - outer layer number varies - Coat / shell Gives symmetry Imperitable Shell around nucleic Loading… acid come. Protect virus Introduce virus genomes into host cell during infection.  Bilayer of lipoproteins and glycoproteins. Genome Capsid Some virus ↑ Envelope Y nucleocapside. N surrounds the without envelope-naked virus  Genome Capsid Envelope Some viruses Enzymes y I Play central role during infection process. Further facts Small Size 10-100nm – 1/10 of bacteria Genome RNA or DNA (never both) Obligate intracellular parasites – viruses can only multiply in a living host cell over 10 million more times of viruses on earth than stars in universe - Oceans etc. Key structures of Viruses (complete the table in your virus Workbook) Viral Capsid Nucleocapsid nucleic acid Viral Envelope protein Classification of Viruses Classification > way in which a capsomenes Symmetry Nucleic acid - are arranged in viral capsid. 2kindt Loading… Structure of Viruses Virus of symmetry  Symmetry corners Polygon-12 equilateral. triangle Icosahedral - - 20 fascet 30 edges most stablee. herpes human pathogenic viruses - Itypee-pentagons or heagous I  linear thin thread like appearance - rod shaped. Filamentous capsids  Head-tail. isssahedral Hybrid between and filamentous Kosahedral Shapes filamenters -.  RNA + DNA can be single or double stranded. Nucleic acid DNA or RNA Viruses can have all possible combos of strandedness and nucleic acid type Double-stranded DNA Double-stranded RNA Single-stranded DNA Single-stranded RNA). RNA viruses Viruses usually show much higher mutation rates than do the DNA viruses  be more Stable than RNA. tend to DNA Virus Viruses and disease – please complete the below table which is in your workbook Virus Name Disease Picornavirus Astrovirus Calcivirus Togavirus Retrovirus Orthomyxovirus Outline the features of HIV, hepatitis B virus, varicella zoster virus influenza viruses and herpes according to their symmetry and nucleic classification Common viruses relevant to dentistry Please complete activity in Virus workbook HIV · HepatisB- Varialla zoster · Herpes - Influenza We will be looking at these in more detail in Viral infections and Year 2  > - cells + tissues of a host that support growth of particular virus. Viral Tropism Some Viruses have broad tissue tropism - can infect many type of cells. Viral tropism is the ability of a given virus to productively infect a particular cell (cellular tropism), tissue (tissue tropism) or host species (host tropism). factors that influence : presence of · cellular receptors permitting viral entry.. of transcription factors availability · cell or virul · cellular receptors of proteins found of Surface. Receptors - allows virus attach to Cell How do they achieve the ability to be selective? Viral replication and dissemination For some viruses some steps are not so the the eclipse , the more obvious longer. Chance the virus has to spread Some may be merged or omitted The period between infection and the production of the new virion (eclipse or latent period) could be as short as 3 hours or as long as several months  1 Adsorption Or attachment of the virus particle to the specific receptors of host cell Positive/firm attachment requires presence of receptors on host plasma membrane needs to fit to be able to bind.  Into all 2. Penetration The process by which the virus or its genome enter the host cell - Penetration can happen by 1. Endocytosis 2. Fusion – direct fusion of viral envelope & host cell 3. Translocation – non enveloped virus pass directly through host membrane  3. Uncoating/eclipse For a period after penetration there is a time the virus cannot be detected – pause in infectivity This ‘eclipse’ phase begins uncoating the lipid membrane & protein capsid surrounding nucleic core Viral nucleic acid becomes free and can act as template for mRNA 4. Transcription FACTORY The mRNA codes for the synthesis of enzymes needed to initiate early steps in viral replication The virus takes advantage of the existing cell structures to replicate itself e.g. integrating in the host DNA  into all, replicated, forced itself built back up again and can now leave. 3 Synthesis of viral 6 Assembly components. aninfect another Synthesis of components Assembly host all Loading… Su Viral proteins are 2 types: Viral assembly is accomplished by incorporating nucleic acid causing into capsomeres high 1. Structural Viral 2. Non-structural – load. Assembly can occur in host enzymes nucleus, cytoplasm or at plasma membrane Components are built on Release Lytic replication – host cells dies treleused. Lysogenic replication – host cell continues to live and function normally but escapes Viral Terms Viral Persistence Examples Persistent infections are characterized as those in which the HIV virus is not cleared but remains in specific cells of infected individuals. Epstein-Barr Human Cytomegalovirus Persistent infections may involve Human Herpesviruses 6 and 7 stages of both silent and productive Varicella-Zoster Virus infection without rapidly killing or Human Papovaviruses even producing excessive damage of the host cells. Hepatitis B Virus 31  HIV ? Viral Latency Herpes ? Virus latency (or viral latency) is the ability of a pathogenic virus to lie dormant (latent) within a cell, denoted as the lysogenic part of the viral life cycle. A latent viral infection is a type of persistent viral infection which is distinguished from a chronic viral infection Recommended Reading Structure and Classification of Viruses - Medical Microbiology - NCBI Bookshelf (nih.gov) Medical Microbiology 4thed. Chapter 41Structure and Classification of Viruses Hans R. Gelderblom.