Chapter 33
viruses
Composition
- Composed
of nucleic acid and protein coat
- DNA
or RNA
- Linear,
circular, single or double stranded
- RNA
viruses are called retroviruses
- Protein
capsid sometimes is surrounded by a lipoproteioglycan envelope
- Host
range describes the possible host cells a virus can infect
Reproduction
- When
infected a host cells genetic machinery is under control of viral DNA
- Viral
DNA is used to produce viral
proteins that direct the production of more viruses.
Bacteriophages
- Infect
bacteria
- Wendell
Stanley provided evidence using TMV(tobacco mosaic virus) that virus
acted like a chemical rather than an organism. (precipitated in a solution)
- Lytic
vs. lysogenic
- Lytic:
DNA free in host cytoplasm instructing viral production
- Lysogenic:DNA
is incorporated into host cell circular DNA molecule and can later enter
lytic cycle.
- Transformation
occurs when viral DNA is incorporated into the host cell DNA
- Transformation
can change host cells character
- Cholera
causing bacterium is due to viral bacteriaphage infection
Emerging viruses
- Ones
that originate in a host and pass to another host
Cancer and viruses
- 15%
of all cancers are caused by viruses that trigger oncogene expression,
bring in their own.
Prions and Viroids
- transmissible
spongiform encephalopathies
- degradation
of brain tissue ie mad cow or creutzfeldt-jakob dz.
- Transmitted
by eating infected tissue
- Not
transmitted through hereditary molecules>through proteins or prion
- Viroids
- Naked
RNA that infects plants by destroying chromosomal integrity