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Viruses, bacteria, viroids, and prions can all cause infection. Any disease-causing agent is called a pathogen. 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells 10,000-100,000 nm prokaryotic cells 200-10,000 nm viruses 50-200 nm viroids 5-150 nm prion 2-10 nm A prion is made only of proteins. - causes misfolding of other proteins - results in diseases of the brain A viroid is made only of single-stranded RNA. – causes disease in plants – passed through seeds or pollen Viruses differ in shape, genetic material, and in ways of entering host cells. – non-living pathogen – can infect many organisms • Viruses have a simple structure. – genetic material (either DNA or RNA) – capsid, a protein shell – maybe a lipid envelope, a protective outer coat Viral Shapes: depends on proteins of capsid enveloped (influenza) capsid helical (rabies) nucleic acid lipid envelope surface proteins capsid polyhedral (foot-and-mouth disease) Surface proteins nucleic acid lipid envelope surface proteins capsid nucleic acid Bacteriophage: A type of virus that prey exclusively on bacteria. Viral DNA is injected into bacteria cell. A bacteriophage is a virus that infects a bacterium. capsid HEAD DNA collar tail sheath TAIL Base plate tail fiber Plant Phages: Prey exclusively on seed plants Tobacco Mosaic Virus Animal Phages: Prey exclusively on animals. The Influenza Virus Viruses enter cells in various ways. – bacteriophages pierce host cells – viruses of eukaryotes enter by endocytosis or fuse with the membrane LYTIC CYCLE Bacteriophage lytic cycle Attachment Assembly & Lysis (release) Are released viruses genetically the same as the original virus? Lysogenic ticking time bomb 2 possible results 1) after cell divisions, lytic cycle kicks in or 2) viruses escape via budding, using host’s cell membrane; leaving host intact, but weakened. Host- the cell the virus is infecting Lysogenic bacteria- a bacterium that has a piece of the viral DNA embedded in its own DNA (has a prophage) Prophage (provirus)- segment of viral DNA that is integrated in the host’s DNA Cell Multiplication- host cell is dividing and dividing, all the while making copies of the viral nucleic acid Differences between Lytic and Lysogenic Cycles: Lytic Cycle Lysogenic Cycle Viruses cause many infectious diseases There are many examples of viral infections. - common cold Viruses cause many infectious diseases There are many examples of viral infections. - common cold influenza Viruses cause many infectious diseases There are many examples of viral infections. - common cold influenza SARS Viruses cause many infectious diseases There are many examples of viral infections. - common cold influenza SARS HIV-infected white blood cell HIV - The body has natural defenses against viruses. How Viruses Change Viruses can mutate when they copy the genetic material Copy something wrong Mistake may prove useful More “fit” virus (more infections) Some viral diseases can be prevented with vaccines. Vaccines are made from weakened pathogens. A vaccine stimulates the body’s own immune response. Vaccines prepare the immune system for a future attack. • Vaccines are the only way to control the spread of viral disease. Immunity - achieved through presence of antibodies Antibodies Proteins produced by the body to neutralize or destroy toxins OR disease carrying agents Disease specific!!! Antigen Any foreign substance in the body that triggers production of antibodies Allergen, bacteria, virus, etc. Types of Immunity Active Immunity Long lasting, sometimes lifetime Usually takes several weeks to develop Exposure to disease organism triggers antibodies to be made Natural immunity: infection with the disease Vaccine-induced: exposure to the weakened or killed form Passive Immunity Only lasts a few weeks or month Protection is immediate Person is given antibodies rather than producing them on their own Newborn baby: from mother to placenta or through breastmilk Blood products: receiving blood with antibodies How are viruses transmitted? Depends on the type of virus, but these are common ways: • Airborne/aerosol • Contaminated food/water • Vectors (infected animal bite) • Sexual contact • Contaminated blood products/transfusions • Other bodily fluids • Breast milk • Exposure at birth