Viruses and Other Acellular Agents Flashcards
an infectious virus particle is called a ____
virion
what are the two components found in EVERY virion and together what are they called
- nucleic acid genome (RNA or DNA)
- protein capsid
together called the nucleocapsid
what are 2 components within SOME virions
- lipid envelope
- replication enzymes
the morphology of a viral capsid
depends on type of virus
- icosahedral (20 face triangle)
- helical (hollow tube with proteins on outside rna on inside)
or complex (neither)
do all viral protein capsids self assemble
no not all but MANY
an example of a complex viral morphology
bacteriophage
if a virus has a lipid envelope is that the same as a plasma membrane ?
NO not the same as it contains host & viral components
non enveloped viruses are also called ___
naked
viral single stranded RNA genome maybe be __ or ___ and describe
+ or -
(+) = function as mRNA & are translatable
(-) = complimentary to mRNA/ not translatable until a complimentary mRNA strand is made (no stop/start codons)
what is shown on a one step growth curve (4)
- latent period = no virions present in media
- rise period = # of virions in media increases exponentially
- plateau period = no more virions produced
- burst size = the # of progeny virions produced per infected cell
5 stages of viral lifestyle
- attachement to host cell
- entry of virus / viral genome into cell
- synthesis of essential replication components
- assembly of nucleocapsids (maturation)
- release of virions from cell
how does the release step differ in naked vs enveloped DNA virus
naked = virions leak out / cell lyses
enveloped = virus buds from cell / exocytosis
describe the attachment step
- specific interactions between viral ligands and host cell receptors
describe the entry step (3 options)
endocytosis - non enveloped or enveloped
fusion- enveloped only
injection - bacteriophages only
describe the synthesis step for DNA
replication of DNA AND transcription/translation to RNA and proteins is necessary for production of new virions
what is specific about ssDNA in the synthesis step
dsDNA replicative form needs to be made before the rest of the processes
describe synthesis of ss(+) RNA
(+) strand acts as mRNA
- only + strand ends up in capsid
describe synthesis of ss(-) RNA
- capsid contains RDRP AND - strand
- neg strand needs RDRP all the time as can’t synthesis a + strand without it
describe synthesis of dsRNA
- have dsRNA and RDRP in capsid (even though don’t need)
what is special about a retrovirus
enveloped RNA virus that contains two copies of + RNA strand
retroviral lifecycles steps differ from a normal virus in step 3 describe
- synthesis
- reverse transcriptase (RT)
= converts viral RNA into double stranded DNA (cDNA) - integrase = inserts this DNA into the host genome as a provirus / when active the provirus is transcribed and replicated
- protease = processes viral proteins for assembly
what is one of the only retroviruses to infect humans
HIV —— leads to aids
does both strategies of release usually lead to the death of the host cell
yes
budding occurs where there are lots of ___ proteins on the envelope
spike proteins
what is a bacteriophage and the two classifications
a virus that infects bacteria
- virulent = lytic cycle only
- temperate = both lysogenic and lytic phases
describe the lytic and lysogenic cycles
lytic cycle - follows 5 step cycle
lysogenic cycle - allows cells to go dormant / phage dna integrates into host chromosome
- when there is stress upon then it would release from the chromosome and enter the lytic cycle to try and replicate before cell dies
when is the lysogenic cycle favoured and when is lytic cycle favoured
lysogenic
- bacteria are nutrient starved / not dividing or growing
- high MOI (multiplicity of infection)
lytic
- bacteria are growing/ multiplying rapidly
- low MOI ( 1 virus and 100 cells)
what is induction
when a prophage switches from lysogenic cycle to lytic cycle
what is lysogenic conversion
a phenotypic change induced in a lysogenized host cell by a prophage
example of a virus encoded toxin
cholera toxin - produced by vibrio cholerae
compare latent, chronic infections and oncogenic and acute
latent infections - do not affect host but may be transmitted (lysogenic)
chronic infections- result in ongoing symptoms
oncogenic- viruses cause host cells to become cancerous
acute - follow 5 step cycle
describe lambdas phage genetic switch
lambda repressor (cl) and cro repressor (Cro)
lysogenic cycle - cl is active, repressing Cro and lambda genome
UV stress - destroys cl allowing Cro expression
lytic cycle- Cro is active, repressing cl and activating lambda genome
2 examples of acellular infectious agents
- viroids (RNA nucleic acid based non viral)
- prions (protein based nonviral)
describe viroids
ssRNA
- no capsid
- causes disease in plants
describe prions
- highly resistant
- causes neurological diseases (Mad cow disease)
what leads to the formation of a prion protein
abnormal folding of a cellular protein (PrpC)
