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#23 Viruses made by: marah marahleh corrected by: Amer Al-salamat date: 4/12/2016 1 Viruses Viruses are very different from bacteria because they are an acellular entity unlike fungi which are similar to bacteria because both can be grown on media. Non-living agents that infect all life forms (plants, phages, and animal viruses) Viral cultivation differs from bacterial cultivation Viruses can't be grown on synthetic media it needs tissue media because viruses need cells to use their metabolic machinery for its own replication and therefore propagation unlike fungi which can be grown on dextrose media ( ex: candida can be grown on CHROM agar ). Only EM allowed for visualization of viruses Can't be seen by light microscope it needs at least 600,000X. Viruses have one major characteristic in common: (They are obligate intracellular parasites). It can't live separately from cells. No virus is able to produce its own energy (ATP) to drive macromolecularsynthesis. Phage: viruse that infect bacteria Bacteriophage: mostly infect E.coli. 2 Slide 4 General Characteristics of Viruses •Contain DNA or RNA (viruses contain NA which can be DNA or RNA but never both. viruses can be classified according to the presence of DNA or RNA which can also be considered as virulence factors. •Contain a protein coat = Capsid that made up of Capsomeres (NA + capsid neucleocapsid). •Some are enclosed by an Envelope (Naked, Enveloped) Naked: without envelope. •Some viruses have Spikes (COH/protein) Spikes either from the envelope or the capsid. •Most viruses are tissue specific. Most but not all for example AB viruse can bind to more than one type of cell (epithelial cells , lymphocyte and mesencymel cells ) .For every tissue there is a specific viruse : viruse –receptor interaction . •Host range is determined by specific host attachment sites and cellular factors: Depends on receptor found on the surface of the cell. Slide 5 Was read. 3 Slide 6 Receptor Viruse Polio: cause polio mellitus. ICAM-1(intracellular adhesion molecule 1 present on WBC, endothelium CD4 HIV: suppress immune system and cause T-helper cell lysis. Acetylcholine (neural impulse transduction) Rabies EGF (epidermal growth factor) Vaccinia (small pox ) Epstein-barr CR2/CD21(complement receptors HVEM (herpesvirus entry mediator Herpes Influenza , corona Sialic acid(common component of extracellular glycosylated proteins, surface cells) Slide 7 90% of viruses are tissue specific. Host Range and Specificity Virus and host cell interaction usually very specific (narrow host range) Specific Tissue tropism is the cells and tissues of a host which support growth of a particular virus. -Some bacteria and viruses have a Broad tissue tropism and can infect many types of cells and tissues like EB viruse. 4 For example rabies virus affects primarily neuronal tissue (specific tropism). Slide 8 First studied viruse: infect tobacco plant bullet shaped cause RT infection Biggest viruse: Ebola viruse which cause: Fever, diarrhea, headache, decrease in kidney and liver function, bleeding, hypotension and sore throat. Mortality rate: 50%. Transmitted by direct contact: - body fluid (semen fluid and milk). -bats: fruit bats specially (carry the viruse but not infected with the disease) 5 Every bacteria has a different phage: phage typing is important in epidemiological studies Ex : S.aureus cause food poisoning if I have a case of food poisoning in salt and another Case in aqaba , in epidemiological studies I need to know if the same strain of the bacteria caused the food poisoningin both cases . so we take the bacteria samples that have collected and infect it with a viruse if it become lysised then that means that the bacteria is the same strain if not then it's mere coincidence . Slide 9 Structural Classes 1) Icosahedral symmetryhave 20 similar faces 2) Helical symmetry 3) Non enveloped naked 4) Enveloped. Slide 10, 11, 12 was read Slide 13—23:27m 1)Satillite virus Contain nucleic acid Depend on co-infection (simultaneously) with a helper virus or superinfection (carrier, chronic) Satellite viruse mean viruse that follow the infection with another so the viruse can't exist without the existence of another viruse (helper viruse) ex: a person can't get hepatitis D without being infected with hepatitis C first. Superinfection: a person infected previously then became a carrier. Mostly in plants, can be human e.g. Hepatitis delta virus (HDV), cannot propagate without HBV 6 2) Viroids Without capsid Unencapsidated, small circular ssRNA molecules that replicate autonomously ss: single strand Only in plants, e.g. potato spindle tuber viroid. 3) Prions No nucleic acid Infectious protein e.g. BSE (bovine spongiform encephalopathy or mad cow disease) 4) Virons (viruse) A complete viral particle, consisting of RNA or DNA surrounded by a protein shell and constituting the infective form of a virus. Slide 14 was read. Slide 15 7 Attachment is receptor specific Assembly: DNA/RNA with capsule. DNA goes under transcription and translation but RNA goes under translation only. Slide 16, 17, 18, 19, 20, 21 was read Slide 22 Viral Replication Obligate intracellular parasites using host cell machinery. Very limited number of genes encodes proteins for: 1) Capsid formation 2) Viral nucleic acid replication 3) Movement of virus into and out of cell. >>Kill or live in harmony within the host cell if the cell dies then the viruse is killed as well >>Outside the cell, viruses are inert: because it's a cellular. Slide 23 How are viruses named? Based on: • 1- The disease they cause: poliovirus, rabies virus 2- The type of disease: murine leukemia virusيصيب الفئران 8 3- Geographic locations: Sendai virus, Coxsackie virus 4- Their discovers: Epstein-Barr virus 5- How they were originally thought to be contracted From mosquito: Dengue virus evil spirit of Ba ylonia ) cramp-like seizure. Influenza virus the influen e of ad air. 6- Combinations of the above: Rous Sarcoma virus. Whenever you feel like giving up, Think of all the people that would love to see you fail. 9