Viruses - Biomedical Science - Student Notes 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 infl...

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 Features of a virus 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. 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 Genome Capsid Genome Capsid Envelope Genome Capsid Envelope Enzymes 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 Key structures of Viruses (complete the table in your virus Workbook) Viral nucleic Capsid Nucleocapsid acid Envelope Viral protein Classification of Viruses Classification Symmetry Nucleic acid Structure of Viruses Virus of symmetry Symmetry Icosahedral Filamentous Head-tail. 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 DNA Virus Viruses and disease – please complete the below table which is in your workbook Virus Name Disease Picornavirus Astrovirus Calcivirus Togavirus Retrovirus Orthomyxovirus Paramyxovirus Papillomavirus Adenovirus Coronavirus 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 Hepatitis B Varicella Zoster We will be looking at these in more detail in Viral infections and Year 2 Herpes Influenza Viral Tropism 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). How do they achieve the ability to be selective? Viral replication and dissemination Adsorption For some viruses some steps are not so Penetration obvious Some may be merged or omitted Uncoating/eclipse The period between infection and the Transcription production of the new virion (eclipse or latent period) could be as short as 3 hours or as Synthesis of viral long as several months components Assembly Release  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  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  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  Transcription 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  Synthesis of viral Assembly components Synthesis of components Assembly Viral proteins are 2 types: Viral assembly is accomplished by incorporating nucleic acid into capsomeres 1. Structural 2. Non-structural – enzymes Assembly can occur in host nucleus, cytoplasm or at Components are built on plasma membrane ribosomes Release Lytic replication – host cells dies Lysogenic replication – host cell continues to live and function normally 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 Epstein-Barr individuals. Human Cytomegalovirus Human Herpesviruses 6 and 7 Persistent infections may involve Varicella-Zoster Virus stages of both silent and Human Papovaviruses productive infection without rapidly killing or even producing excessive Hepatitis B Virus damage of the host cells. 31 Viral Latency 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.