mutations on human immunodeficiency virus type 1

Medical Microbiology Li Mei Department of Microbiology November, 2006 Virology Chapter 19 General Properties of Viruses Structure Replication What is virus? Viruses the smallest infectious and acellular microbe consisting only one kind of nucleic acid (DNA or RNA), and which obligately replicate inside host cells  Virions The complete mature viral particles (The intact infectious virus particles.) Distinctive features • • • • • Acellular microbes Pass through 0.2μm filters Obligatory intracellular parasites Contain either DNA or RNA Self-replication I Size, shape and structure A Size: The unit of measurement parvoviruses nm poxviruses Comparative sizes of virions and bacteria • • • • • • • • • Staphylococcus aureus Rickettsia Chlamydia Poxviruses Bacteriophage of E coli Influenza virus Adenovirus Encephalitis B virus Poliovirus I Size, shape and structure B Shape: Tobacco mosaic virus: rodshaped II Replication  Assembly Naked virus: capsid + viral genome → nucleocapsid (virion) Enveloped virus: nucleocapsid + envelope → virion Site: a DNA viruses (except poxvirus): cell nucleus; b RNA viruses and poxvirus: cell cytoplasm; Manner: a assemble as empty shell (procapsids), then viral genome fill in b Viral capsomers array around the viral genome to form helical symmetry II Replication  Release The process of progeny viruses getting out of host cell – Naked viruses: released by cell lysis – Enveloped viruses: usually released by budding During budding enveloped viruses acquire their envelope – Defective measles virus: release from cell to cell via cell bridges ↓ SSPE (Subacute sclerosing panencephalitis) Host cell lysis Budding • release II Replication B Abnormal replication: – Defective viruses – Abortive infection II Replication Defective viruses: are genetically deficient and incapable of producing infectious progeny virions Helper virus: can supplement the genetic deficiency and make defective viruses replicate progeny virions when they simultaneously infect host cell with defective e.g., AAV & adenovirus viruses Defective Viruses • Defective Viruses lack gene(s) necessary for a complete infectious cycle • helper viruses provide missing functions A A B B Defective interfering particles (DIP) DIP: • Defective viruses which can occupy the cell machinery necessary for normal virus replication to prevent virus production, are called "defective interfering particles" (DIP) II Replication Abortive infection: Virus infection which does not produce infectious progeny because the host cell cannot provide the enzyme, energy or materials required for the viral replication non-permissive cells The host cells that cannot provide the conditions for viral replication permissive cells The host cells that can provide the conditions for viral replication III Viral interference: Viral interference When two viruses infect simultaneously one host cell, the virus A may inhibit replication of virus B Range of interference occurrence between the different species of viruses; between the same species of viruses; between the inactivated viruses and live viruses III Viral interference Mechanisms of viral interference: a.Virus A may inhibit virus B adsorption by blocking or destroying receptors on host cell b.Virus A may compete with virus B for replication materials like polymerase, translation initiation factors, etc c.Virus A may induce the infected cell to produce interferon that can prevent viral replication III Viral interference: Significance of interference: Advantage a Stop viral replication and lead to patient recovery b Inactivated virus or live attenuated virus can be used as vaccine to interfere with the infection of the virulent virus Disadvantage May decrease the function of vaccine when bivalent/trivalent vaccine is used IV Reaction to physical & chemical agents Physical agents: Temperature, pH, Irradiation Chemicals: Phenol and its derivatives; Formaldehyde/formalin; 70% ethanol; Oxidizing agents; Lipid solvents; Biological agents Antibiotic, interferon, etc -196℃ Differentiation of viruses from bacteria Virus Bacterium Size 0.02 ～ 0.3um 0.5 ～ 3.0um Structure Non-cellular microorganism DNA or RNA Prokaryotic microorganism DNA and RNA Growth on cell free medium Mode of multiplication Cannot grow Can grow Replication Binary fission Ribosome None Has ribosome Antibiotic Resistant Sensitive Interferon Sensitive Resistant Nucleic acid ...Virology Chapter 19 General Properties of Viruses Structure Replication What is virus? Viruses the smallest infectious and acellular microbe consisting only one kind of nucleic acid... (e.g., tobacco mosaic virus) • Icosahedral symmetry (e.g., adenovirus)  Complex symmetry (e.g., poxviruses ) Influenza virus Unconventional viruses • Viroid – plant disease – Human Hepatitis D a... Replication A Normal Replication – Adsorption /Attachment – Penetration – Uncoating – Biosynthesis – Assembly – Release II Replication  Attachment / Adsorption Attachment / Adsorption II Replication