Biology II Ch 19
restriction enzymes
bacteria's defense against phages recognize & cut up certain phage DNA
what does viral genome consist of
consists of double or single stranded RNA or DNA
discovery of viruses
adolf mayer & dimitri ivanowksy hypothesized that a particle smaller than bacteria caused TMV wendall stanley confirmed that it was a virus by crystallizing the infectious particle
virus treatment
little can cure it antibiotics for bacteria do not work bc they have few/no enzymes of their own antivirals
phage's 2 reproductive cycles
lytic & lysogenic cycle
vaccines
harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen eradicated small pox
acyclovir
inhibits viral polymerase that synthesize viral DNA for herpes
prophage
integrated viral DNA
provirus
integrated viral DNA unlike prophage, remains permanent resident of the host cell host's RNA polymerase transcribes the proviral DNA into RNA molecules
azidothymidine (AZT)
interferes with reverse transcriptase for AIDs
antivirals
nucleotides that interfere with polymerase that synthesize viral DNA
bacteria
prokaryotes with cells smaller & more organize than eukaryotes
lysogenic cycle
replicates phage genome without destroying host viral DNA is incorporated by genetic recombination into host cell's chromosome every time host divides, it copies the phage DNA & passes copies to daughter cells
viruses
smaller & simpler than bacteria genes packaged into protein coat, sometimes membranous envelope obligate intracellular parasite
If you were a researcher trying to combat HIV infection, what molecular processes could you attempt to block?
medications target reverse transcriptase cannot immunize bc there are many mutations of the virus (mutations caused by reverse transcriptase not being good at its job bc its transcribes RNA to DNA differently each time)
emerging viruses
those that appear suddenly or suddenly come to the attention of scientists (AIDs, west nile virus, SARS)
what do viruses use enzymes, ribosomes, & small host molecules for?
to synthesize progeny viruses
herpes virus
DSDNA reproduce within host cell nucleus copies of virus DNA remain as mini chromosomes in nuclei of certain nerve cells remain latent until physical/emotional stress causes blister flare ups throughout life
If Beijerinck had observed that the infection of each group was weaker than that of the previous group and that ultimately the sap could no longer cause disease, what might he have concluded?
Infection was caused by a toxin since replication did not occur.
A researcher lyses a cell that contains nucleic acid molecules and capsid units of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur? a. The plants would develop some but not all of the symptoms of the TMV infection. b. The plants would develop the typical symptoms of TMV infection. c. The plants would not show any disease symptoms. d. The plants would become infected, but the sap from these plants would be unable to infect other plants.
The plants would develop the typical symptoms of TMV infection. (correct)
obligate intracellular parasite
can produce only within host cell
membranous (viral) envelope
derivative of host cell's membrane surrounds capsid of virus contains combination of viral & host cell molecules many viruses that infect animals have this viral glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell
cause of emerging viruses
existing viruses that increase their host territory mutation of virus dissemination from a small isolated population spread from other animals
avian flue fears
high kill rate
prokaryotes
no organelles, no nucleus
lytic cycle
phage reproductive cycle culminates in death of host cell produces new phages & digests host's cell wall releasing progeny viruses
virulent phage
phage that reproduces only by lytic cycle
temperate phages
phages that use both lytic & lysogenic cycles
capsid
protein shell that encloses the viral genome built from capsomeres
HIV
retrovirus that causes AIDs
tobacco mosaic disease
stunts growth of tobacco plants gives leaves mosaic coloration caused by filtered sap being rubbed on healthy plants therefore infecting them
retrovirus
use reverse transcriptase to copy their RNA genome into DNA
broadest variety of RNA genomes are found in
viruses that infect animals
bacteriophage
viruses that infect bacteria most complex capsids found among viruses elongated capsid head encloses their DNA protein tailpiece attaches phage to host & injects phage DNA inside