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Virus - Veni, Vidi, Vici ? Izabela Tworowska, PhD Department of Biochemistry and Cell Biology Part I.

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Presentation on theme: "Virus - Veni, Vidi, Vici ? Izabela Tworowska, PhD Department of Biochemistry and Cell Biology Part I."— Presentation transcript:

1 Virus - Veni, Vidi, Vici ? Izabela Tworowska, PhD Department of Biochemistry and Cell Biology Part I

2 Viruses - structure 1. contain nucleic acid, either DNA or RNA (but not both), and a protein coat (encases the nucleic acid). 2. some viruses enclosed by an envelope of fat and protein molecules. The smallest virus: satellite tobacco necrosis virus (STNV) plant virus, not enveloped; 17 nm in diameter; consists of 60 protein subunits and RNA; Satellite virus- depends on co-infection with the helper virus (providing missing replication function) Animal (human) satellite virus: Hepatitis delta virus (HDV) cannot survive w/o the helper virus Hepatitis B virus (HBV)

3 Capsid the protein shell that encloses the nucleic acid; capsid + nucleic acid = nucleocapsid three functions: nucleic acids protected from digestion by enzymes contains special sites (spikes) on its surface (attach to a host cell) provides proteins allowing the virus to penetrate the host cell Envelope glycoprotein envelope surrounds the nucleocapsid; composed of two lipid layers; glycoprotein’s spikes on the envelope Nucleic Acids few groups of viruses use DNA; most are single-stranded RNA viruses; RNA viruses may contain: plus strand RNA – direct synthesis (translation) of viral protein negative strands RNA- first synthesis messenger RNA, then viral protein synthesis

4 VIRUS- where, why, how ?. Occupy the “gray area” between living and non-living organisms Speculated form of proto-life (unlikely that they preceded cellular life during the Earth's early evolution).. Viruses started as rogue segments of genetic code (adapted to a parasitic existence) How do they replicate? Cannot survive without a host cell synthesize proteins, generate or store energy in the form of the adenosine triphosphate (ATP) Where do they come from?


6 Complementary Strand (mirror strand)

7 Viruses can have different genomes Herpes simplex Polio, HIV, Influenza Reovirus HBV -partially ss, mainly dsDNA Eryhtrovirus HIV

8 The relative size of some viruses

9 The relative size of some viruses –how big?

10 NOBODY IS SAFE ! Viruses can infect animals, plants, or bacteria. (viruses cannot penetrate plant cell walls, plant viruses are transmitted by insects or other organisms) Classification of viruses into families: type and size of their nucleic acid, size and shape of the capsid presence of the envelope Bacterial virus T4 Bacteriophage

11 Shapes of viral capsid rods, filaments spheres head- tail structure Tobacco mossaic virus Hepatitis B T4 bacteriophage Enterobacteria phage Polio virus the simplest way to arrange non-symmetrical icosahedral symmetry, components and place in circle to form discs. (20 triangular facets ) Advantage of the subunits structure of the viruses: greater genetic stability


13 1. the virus attaches to the target cell 2. the viral nucleic acids enters the cell 3. the host cell synthesizes the proteins encoded in the viral genome and replicates the virus’s DNA or RNA 4. the new viral proteins and the nucleic acids assemble into new viruses 5. the new viruses are released from the cell Virus life cycle

14 HIV life cycle

15 Guess, who am I ? Virion, Viroid or Prion ? Virion virus infective form (outside the cell) contains at least one unique protein synthesized by specific genes in its nucleic acid. Viroid (meaning "virus-like") disease-causing organism contains only nucleic acid and has no structural/functional proteins Prion ("virus-like") composed primarily of a ‘’infectious agent’’ – protein Spongiform encephalopathies

16 The infectious agent (protein) has been called a prion. A prion has been defined as "small proteinaceous infectious particles which resist inactivation by procedures that modify nucleic acids". The discovery that proteins alone can transmit an infectious disease has come as a considerable surprise to the scientific community. The Prion Hypothesis from Corey Wilson’s lecture


18 Spongiform Encephalopathies

19 US Pavilion at Expo '67,US Pavilion at Expo '67 by Buckminster Fuller and Shoji Sadao, at Montreal, Canada, 1967. Buckminster Fuller (1893-1983) architect, mathematician invented the geodesic dome

20 Buckminsterfullerene, C60, the molecule that started it all. (eta2-C70-Fullerene)-carbonyl-chloro- bis(triphenylphosphine)-iridium J.Am.Chem.Soc., 113, p8953,1991 FULLERENES (BUCKYBALL)

21 The Royal Swedish Academy of Sciences has awarded the 1996 Nobel Prize for Chemistry jointly to: Professor Robert F. Curl, Jr., Rice University, Houston, USA Professor Sir Harry W. Kroto FRS, University of Sussex, Brighton, UK Professor Richard E. Smalley, Rice University, Houston, USA for their discovery of fullerenes

22 DNA buckyballs used for drug delivery as containers for chemical reactions Science News, August 29, 2005

23 See next on Thursday!

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