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VIRUSES & PRIONS. SECTION: 18.2. Virus: a nonliving strand of genetic material within a protein coat Virus Size: one of the smallest disease-causing structures need electron microscope to see about 10,000 cold viruses needed to span a period at end of sentence. Virus Origin:
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VIRUSES & PRIONS SECTION: 18.2
Virus: a nonliving strand of genetic material within a protein coat • Virus Size: • one of the smallest disease-causing structures • need electron microscope to see • about 10,000 cold viruses needed to span a period at end of sentence.
Virus Origin: • one theory: came from parts of existing cells • genetic material of viruses is similar to cellular genes • genes somehow developed the ability to exist outside the cell
Virus Structure: (see p.526 fig.18.11) • capsid: outer layer of protein • genetic material • (DNA or RNA) found • inside capsid • classified by type • of nucleic acid • virus at right is a • Bacteriophage which • infects bacteria
Viral Infection: • must enter a host to replicate • many viruses cannot be transmitted between species, too specific • injects genetic material into host • uses host cell to replicate by lytic or lysogenic cycle • Lytic Cycle: host cell makes many copies of viral DNA or RNA • leave cell by exocytosis & infect other cells • symptoms usually occur in 1-4 days
Lysogenic Cycle: viral DNA enters host cell’s chromosome • becomes permanently part of host cell’s chromosome • may remain dormant for months or years • becomes activated and enters lytic cycle to produce new viruses • leave by exocytosis and infect other cells • (See p.529 fig. 18.13) • http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/adlyt.html
Retroviruses: viruses containing RNA instead of DNA • HIV=human immunodeficiency virus • some cancer-causing viruses • contain protein capsid surrounded by lipid envelope obtained from cell membrane of host cell • HIV attaches & “invades” • host cell and may lie • inactive for years • once activated, host cell • creates & assembles new • HIV particles
Prions: a protein that causes infection or disease • normally in cells in shape of a coil • mutations cause misfolding in shape of paper folded many times • diseases caused by: mad cow & chronic wasting disease • http://www.whfreeman.com/kuby/ • content/anm/kb03an01.htm • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter26/animations.html#
☺QUIZ TIME! ☺ • WHICH REPLICATION CYCLE STARTS WITHIN 1-4 DAYS? • Lysogenic B. Lytic 2. WHAT DOES A BACTERIOPHAGE INFECT? A. A PRION B. A RETROVIRUS C. A BACTERIA
3. WHICH TYPE OF NUCLEIC ACID DO RETROVIRSES HAVE? A. DNA B. RNA
