unit 4 study guide Flashcards
virus particles
virions
function of capsid
protective coating for nucleic acid
can a virus have both DNA and RNA as nucleic acids at once?
no
difference between dsRNA and ssRNA
dsRNA = double stranded RNA
ssRNA = single stranded RNA
protein subunits of capsid
capsomere
common type of polyhedral capsid
icosahedron (20 sides 12 corners)
structure that plays the role of envelope in enveloped virus
cell membrane
types of viruses currently recognized
7 types
5 stages of lytic cycle
- attachment
- entry
- synthesis
- assembly
- release
attachment (lytic)
when does host cell lysis occur? (which stage of lytic cycle)
release
what do late genes produce during biosynthesis?
structural proteins - capsomeres, tail fibers, viral enzymes (lysozyme)
step of lytic cycle where capsomeres assemble into capsids
assembly
attachment stage of lytic cycle (what happens?)
virus binds to host cell receptors
entry stage of lytic cycle (what happens?)
DNA enters the host cell
biosynthesis stage of lytic cycle (what happens?)
DNA is replicated and phage proteins are made
assembly stage of lytic cycle (what happens?)
new phage particles are assembled; nucleic acid packed inside the capsid
release stage of lytic cycle (what happens?)
the cell explodes; new viral phages are released
why does the host cell always die at the end of the lytic cycle?
because the cell bursts (lysis)
temperate phages are most likely to enter the lytic cycle if:
a cell is growing healthily; if cell is in log phase
phage that can choose between lysogenic cycle and lytic cycle
temperate phage
phage that can only choose the lytic cycle every time
virulent phage
what happens during lysogeny?
viral DNA becomes part of host chromosome, becoming a prophage
prophage
phage DNA combined with bacterial chromosome
what cycle does a lysogenic phage use to leave its host to infect others?
lytic cycle
third step in replication cycle in animal virus
uncoating
why are most viruses tissue/cell specific + only able to attack one kind of body tissue?
viruses can only attach to certain receptors found on specific cells
capsid disintegrates in cytoplasm during:
uncoating
enveloped viruses are released from an infected host cell via:
budding
naked animal virus penetration
if the capsid is brought into the cell via endocytosis
6 steps of animal virus replication + brief explanation of what occurs
- attachment - virion adheres to receptor on host cell
- penetration/entry - depends on virus type; naked = endocytosis, enveloped = fusion
- uncoating*** - capsid releases its nucleic acid payload
- synthesis - early genes expressed (enzymes for nucleic acid replication); late genes expressed (capsomeres, enzymes, other proteins required)
- assembly - new virions assembled
- release - new virions released; naked = lysis, enveloped = budding
two different entry methods for animal viruses to enter the host cell
endocytosis (if virus is naked) and fusion (if virus is enveloped)
if animal virus is naked, it enters host cell using
endocytosis
if animal virus is enveloped, it enters host cell using
fusion
two different release methods for animal viruses to exit host cell
lysis (if naked) and budding (if enveloped)
uncoating occurs after ___ and before ___ of the animal virus replication cycle
after penetration and before biosynthesis
does the DNA of a latent animal virus become integrated with host cell’s chromosomes?
no; animal virus DNA cannot become part of host cell chromosomes
examples of latent viral infections
HIV, HSV-1, HSV-2
“hibernation” between outbreaks
latency
what ssRNA is used as a template strand?
(-)ssRNA
why must (+)ssRNA viruses make (-)ssRNA during their replication process?
(-)ssRNA is used as a template so that more (+)ssRNA can be synthesized
error prone enzyme of RNA virus (also the reason why common cold has no vaccine)
RdRp (RNA dependent RNA polymerase)
what enzyme must (-)ssRNA viruses carry in their capsid?
RdRp
viral spike protein of influenza that attaches to host cell
hemagglutinin
viral spike protein of influenza that is responsible for virion release from infected host cell
neuraminidase
first step in biosynthesis of (-)ssRNA virus
RdRp synthesizes (+)ssRNA using viral (-)ssRNA as a template
why can’t (-)ssRNA be translated by ribosomes
doesn’t contain start codon - it is not mRNA
antigenic shift
process involving genetic change in flu virus; reassortment of viral nucleic acid segments which produce novel virions
antigenic drift
mutations in hemagglutinin genes of flu viruses that help to fool host’s immune system; cause of constant vaccines
molecules released into nucleus of host cell during uncoating and HIV
viral dsDNA and integrase enzyme
once integrated into host cell’s chromosome, retroviral DNA is called a
provirus
CD4
protein found only on membrane on few human cells that serves as receptor for HIV attachment
lymphocyte that is a target of HIV
T helper cell
gp41
directs fusion of viral envelope within cell membrane during penetration; protein found on HIV
enzyme of HIV that is capable of synthesizing DNA on RNA template
reverse transcriptase (RT)
retrovirus integrated w/ host’s chromosome
provirus
scientists think HIV spilled over into humans in:
1908
how long can an HIV+ person live w no signs/symptoms of infection?
3-10 years
immune system cells infected by HIV
T helper cells and macrophages
what do OTC HIV tests detect?
antibodies for HIV, NOT HIV itself
what is detected in blood test for HIV?
HIV-specific proteins (gp120 / p24) or HIV (+)ssRNA
most common route of accidental HIV transmission to healthcare workers
needle stick
region of the world that has the highest prevalence of HIV+ individuals
africa; sub-saharan africa
why are anti-HIV drugs hard to develop?
virus mutation rate (change in drug targets), also expensive
current best ways to stop HIV spread (5)
education, abstinence, PrEP, stopping needle sharing, condom usage, antiretroviral therapy
specific effect Truvada has on replication cycle of HIV?
stops HIV virus from producing dsDNA during biosynthesis
why does HIV lead to AIDS?
it destroys T helper cells, weakening the immune system
when a person is HIV+, that means
that the virus has invaded the patient, meaning their immune system is responding to the virus via making antibodies
