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  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. Review! What does obligate mean? Capable of functioning or surviving only in a particular 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

 AttachmentPhage attaches by tail fibers to host cell  PenetrationPhage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell  BiosynthesisProduction of phage DNA and proteins  MaturationAssembly of phage particles  ReleasePhage lysozyme breaks cell wall Multiplication of Bacteriophages (Lytic Cycle)

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

18 Viroids  Small, circular RNA molecules without a protein coat  Infect plants  Potato famine in Ireland  Resemble introns cut out of eukaryotic copyright cmassengale

19 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

20 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

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 Influenza Virus - Flu Human Immunodeficiency Virus AIDS Rabies Virus

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