BIOL 151 Final: Chapter 10 notes for final exam

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BIOL 151
Chris Felege

Viruses Introduction • A virus is an obligate, intracellular parasite • Viruses enter a host cell and use the host's biosynthetic machinery to reproduce and synthesize its proteins • Most biologists would argue that viruses are not alive, because they depend on their host cell to satisfy the key attributes of life ◦ NOT made of cells ◦ No metabolism of their own ◦ DON’T grow • Viruses ◦ Have a genome (DNAor RNA) ◦ Adapt to their environment ◦ Evolve ◦ Organized (on at least the molecular level) ◦ Respond to their environment • Each type of virus infects a specific unicellular species or cell type in a multicellular species ◦ Nearly all organisms examined thus far are parasitized by at least one kind of virus • Although viruses are acellular parasites, they have directly contributed to the diversity of life ◦ They introduce foreign genes into cellular genomes and thus promote lateral gene transfer • Viruses also contribute their own genetic material to organisms ◦ 5-8% of the human genome consists of viral genome remnants • In the human body, virtually every system, tissue, and cell can be infected by at least one kind of virus • Much research on viruses is motivated by the desire to minimize the damage they can cause • An epidemic is a disease that rapidly infects a large number of individuals over as widening area ◦ Viruses have caused the most devastating epidemics in recent human history • A pandemic is a worldwide epidemic ◦ The "Spanish flu" outbreak of 1918-1919 was the most devastating pandemic to date • The strain of influenza virus that emerged in 1918 was particularly virulent (it tended to cause sever disease) • Worldwide, the Spanish flu killed up to 50 million people • Human Immunodeficiency Virus (HIV) cause acquired immune deficiency syndrome (AIDS) ◦ AIDS is likely to surpass the 1918-1919 influenza epidemic in its impact on humans • HIV parasitizes and destroys cells called helper T cells of the immune system, they body's defense system against disease • During HIV infection, the total number of helper T cells in the blood gradually declines ◦ The number of T cells the body manufactures cannot keep up with the number of T cells the virus destroys • When the T-cell count drops, the immune system's responses to invading bacteria and viruses become less and less effective ◦ HIV kills people indirectly - it makes them susceptible to pneumonia, parasites, unusual types of cancer, or other disease causing agents that our bodies could normally fight off • AIDS has already killed almost 30 millions people worldwide ◦ The highest rates of infection are in eat and centralAfrica • Over 20% of the Botswana population is HIV positive ◦ There are about 34 million HIV-infected people ◦ And additional 2.7 million people are infected each year • Because HIV is primarily a sexually transmitted virus, it disproportionately affects young adults • Researchers who study viruses usually focus on two goals: 1. Developing a vaccine to help hosts fight off disease 2. Developing antiviral drugs to prevent viral infection • The first step in studying a virus is to isolate it, which takes researchers into the realm of nanobiology ◦ Structures are measured in biollionth of a meter - one nanometer ◦ Most viruses range in size from only about 20 to 300 nm in diameter • Viruses are tiny relative to eukaryotic or even bacterial cells • Researchers use Koch's postulates to isolate a virus and confirm that it is the causative agent of infection • Once a virus is isolated, biologists analyze 1. The structure of the virion i. Avirion is a extracellular, infectious particle 2. The nature of the genetic material that is transmitted by virions between hosts 3. Variation in viral replication • Viruses come in a wide variety of shapes, and many can be identified by shape alone • In terms of overall structure, most viruses fall into just two general categories 1. Non-enveloped ("naked") viruses i. Genetic material enclosed only by a protein shell called a capsid 2. Enveloped viruses i. Genetic material enclosed by a capsid and one or more membrane-like envelopes • Most viruses produce virions with helical or icosahedral capsids • Some viruses have more complex capsid shapes • The capsid serves two functions: 1. Protects the genome while outside the host 2. Releases the genome when infecting a new cell • In addition to morphology, viruses can be categorized based on the nature of their genome ◦ Many viruses break the central dogma of molecular biology • Informat
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