viruses Flashcards
are viruses alive?
- can’t reproduce without assistance
- lack machinery for energy harvesting, proteins synthesis, etc (must borrow this machinery from host cell)
- “obligate intracellular parasites” (must be in host)
- so no
general virus characteristics
- non-cellular parasites
- they have either DNA or RNA never both
- goal of virus is not to kill host
dormancy
some virus form crystalline structures and remain unchanged in an inactive state for years until they meet a receptive host (ex: tobacco mosaic office)
capsid
where nucleic acids are stored. in some viruses it is covered in a protein envelope
virus size
virus size varies, but they are very small. 20nm to 300nm
bacteriophage
virus that attacks bacteria only
parts of bacteriophage
-head (capsid and nucleic acid core)
-tail (contractile sheath, tail fiber, base plate with tail pins)
see ppt for chart
virus diversity
many shapes and sizes, easily mutate
viral reproduction
- highly efficient
- rapid evolution
- can give host new phenotypes
- RNA replication lacks proofreading mechanisms so mutating rate is higher
viral replication cycle steps
- attachment (absorption)
- penetration (entry)
- replication
- assembly and maturation
- release
attachment
- “absorption”
- virus binds to host cell
- viral surface proteins bind to cell surface receptors = high specificity
entry
- “penetration”
- viral genetic material enters cell
- various mechanisms, portions of the virus may remain outside host cell
lytic cycle
- in bacteria only
- when a dormant virus becomes infected
- most signals are unknown
lysogenic cycle
- in bacteria only
- phage integrates nucleic acid into the host cell’s DNA creating a provirus that becomes dormant
retrovirus
- RNA viruses
- after the virus enters a cell the RNA is turned to DNA via reverse transcriptase
- HIV
transduction
viruses will introduce pieces of a hosts genetic material into that of another related or unrelated host. could influence evolution
phenotypic mixing
- animal cells sometimes simultaneously infected by two viruses
- viral genetic material and viral capsids mismatched
- can facilitate interspecies gene transfer
herpes virus
- 100 strains
- cold sores, chickenpox, shingles, mono, genital herpes
HIV
- causes AIDS
- attacks T cells and reduces the function of immune system
- secondary function can be deadly
- descendants of bubonic plague survivors are immune
HPV
- papilloma virus
- causes warts
- can cause cervical cancer
- about 50% of sexually active people contract it at some point
epidemic
affects many people where disease wasn’t prevalent before
pandemic
an entire country, continent or whole world
endemic
found in an isolated place like the tropic flu
epidemiology
studying the spread of the disease
viroids
- infectious RNA molecules that cause disease in various plants
- their genome are much smaller than those of viruses (up to 400 nucleotides of circular single stranded RNA) and do not code for any proteins
prions
- infectious agent made of protein
- able to fold in many ways
- makes them transmissible to other organisms
- often found in brain tissue
- examples: Creutzfeldt-Jakob disease, and mad cow disease
