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Viruses A virus is not a cell. It lives only within a living cell and has no attributes of a living organism. It is an obligate intracellular parasite. Viruses Review! What does obligate A virus is not a cell. Itmean? lives only Capable functioning within a livingof cell and has no or attributes of a living surviving only organism. in a particular It is an obligate intracellular parasite. condition What is a parasite? Organism that lives and derives nourishment at the detriment of the host What is an obligate parasite? Viruses It is made up of DNA or RNA inside a protein coat called a capsid. RNA Virus Some take lipids from the cell it infects and make a covering over the capsid that has glycoprotein receptors. Receptors are used to attach to the host’s membrane. RNA Virus Structure Viruses A virus is not a cell It is made up of genetic material inside a protein coat Viruses do not carry on most metabolic activities Viruses Viruses that attack only bacteria are known as bacteriophages. Virus Reproduction – Lytic Cycle Multiplication of Bacteriophages (Lytic Cycle) Attachment Penetration Biosynthesis Maturation Release Phage attaches by tail fibers to host cell Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell Production of phage DNA and proteins Assembly of phage particles Phage lysozyme breaks cell wall Virus Reproduction – Lysogenic Cycle Lytic or Lysogenic Cycle? The animation on the next slide demonstrates which cycle? Lytic vs Lysogenic Lytic cycle – Phage causes lysis and death of host cell Lysogenic cycle – Prophage DNA incorporated in host DNA Virus Classification Smallpox Although smallpox was declared extinct in the wild in 1979 (last natural infection recorded in 1977) there is increasing concern about its potential use as a biological weapon. Although only two locations officially hold variola (one at the CDC in the USA and one in Russia) it is feared that secret stockpiles exist. Smallpox CLASSIFICATION OF THE SMALLPOX VIRUS GENOME: Linear Double Stranded DNA Family: Poxviridae Subfamily: Chordopoxvirinae Genus: Orthopoxvirus Species: Variola Prions and Viroids Bits and Pieces that cause disease Viroids Small, circular RNA molecules without a protein coat Infect plants Potato famine in Ireland Resemble introns cut out of eukaryotic copyright cmassengale 18 Prions Prions are “infectious proteins” They are normal body proteins that get converted into an alternate configuration by contact with other prion proteins They have no DNA or RNA The main protein involved in human and mammalian prion diseases is called “PrP” copyright cmassengale 19 Prion Diseases Prions form insoluble deposits in the brain Causes neurons to rapidly degenerate. Mad cow disease (bovine spongiform encephalitis: BSE) is an example People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies copyright cmassengale 20 Virus Reproduction Negative Virus Influences They cause infections in both plants and animals Some viruses cause tumors and warts They also destroy cells and are responsible for human diseases such as – polio – measles – mumps – influenza – hepatitis – colds – AIDS Human Papilloma Virus - Warts Rabies Virus Influenza Virus - Flu Human Immunodeficiency Virus AIDS Positive Virus Influences Certain viruses are used in the control of insect pests Others are used in genetic research Scientists have been able to use viruses to biologically control caterpillars of the European pine sawfly and the gypsy moth