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ch.19 - viruses.docx

4 Pages

Biological Sciences
Course Code
BIOSC 0150
Christine Dahlin- Universityof Pittsburgh Johnstown

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1 General Biology 1 Chapter 19 – Viruses Viruses – pathogen that’s smaller and simpler than bacteria - Latin word – poison - Infection - Cause disease and spread between organisms - Cannot reproduce or carry out metabolic activities outside host cell  viruses aren’t alive - Grey area – not quite alive, but more than simple chemicals Basic structure – nucleic acid surrounded by a protein coat - Form of genetic material viruses – double strand/single strand DNA or RNA - Viruses categorized based on type of nucleic acid Protein coats – known as capsids - Have variety of shapes - Built from protein subunits capsomeres - Accessory structures like membranous envelope and glycoproteins Types of capsids - Tobacco mosaic virus - Adenoviruses – infect animal respiratory tracts - Influenza viruses – viral envelope made of host cell membranes - Bacteriophage T4 – phage infect bacteria Viral envelopes - Outer membrane on some viruses - Envelopes on animal viruses help them enter host cells - Viral glycoproteins bind to receptor molecules on host cells - Inside host cells, new viral capsids are wrapped in membrane as they bud from the cell Viruses can’t replicate because they don’t have - Metabolic enzymes and ribosomes (which make protein) - Therefore they replicate in host cells – host cell gets replicate o Limited number of host species o Lock and key recognition system fit between receptor molecules on host cells and viral surface proteins Host range varies - West-Nile virus and equine encephalitis has broad host range o Can infect mosquitoes, birds, horses and humans - Measles has narrow host range o Can only infect humans - Viruses of multicellular eukaryotes often have narrow host range o Cold viruses – living of upper respiratory tract o Aids virus – white blood cells Viral replication - Binds to host cell and genome enters cell through injection, endocytosis, fusion with plasma membrane 2 General Biology 1 Chapter 19 – Viruses - Commandeers the host cell by reprogram cell to copy nucleic acids, make viral proteins and other components to create more viruses. Viral envelopes - Outer membrane on some viruses - Envelope on animal viruses help them enter host cells o Viral glycoproteins bind to receptor molecules on host cells o Inside host cells, new viral capsids are wrapped in membrane as they bud from the cell Viral diseases in animals - Viruses can o Cause disease symptoms such as  Cause release of digestive enzymes from lysosomes  Cause cells to produce toxins that cause disease symptoms  Have toxic molecular components (envelope proteins) We get sick because: - Many temporary symptoms are results of body’s defenses against infection which are not from cell death. Symptoms include most fever and aches. Recovery depends on: o Ability to infected tissue to regenerate itself o Respiratory infections – epithelium can repair itself, damage not permanent o Poliovirus – A mature nerve cell gets damaged and is permanent. Defend against viruses 1. Immune system – body attacks pathogens, prior exposure sometimes needed 2. Vaccines – harmless variant of a pathogen, stimulate immune system 3. Vaccinaton programs – eradication and control of once common diseases such as smallpox, polio, measles and whooping cough. - Can’t cure a virus
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