VIRUSES &

PRIONSSECTION: 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 whichinfects 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/course

s/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! ☺1.WHICH REPLICATION CYCLE STARTS WITHIN 1-4 DAYS?

A. 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

YOU’RE RIGHT! ☺

Sorry, wrong answer