lecture 1 part 2 Flashcards
DNA viruses can be ___ or ____
enveloped or naked
HERPES is an example of a ___ virus
enveloped double strand linear DNA
Adenovirus is an example of a ____ virus
naked double strand linear DNA virus
the majority of viruses that infect bacteria are DNA or RNA?
DNA
Name the 9 general steps of viral replication
- recognize target cell
- attachment
- penetration/fusion
- uncoating of virion – exposes nucleic acid
- transcription
- protein synthesis
- replication of nucleic acid – happens for ALL VIRUSES
- assembly
- release
there are __ mechanisms in which a virus can get into the cell:
2:
-straight endocytosis
-receptor mediated endocytosis
viruses can be ___ or ___ and cells can be ___ or ____
viruses can be PRODUCTIVE or NON-PRODUCTIVE
cells can be PERMISSIVE or NON-PERMISSIVE
explain the difference between a productive and non-productive virus
a productive virus lyses the infected cell (lytic response)
a non-productive virus DOES NOT LYSE THE HOST CELL and can be:
-lysogenic (integration of viral genome into host genome, or the formation of an extrachromosomal plasmid)
-oncogenic – integrate in genome (chromosome) next to growth factor gene. virus gets growth factor gene on it and virus is in control ex: RNA tumor virus
-persistent – latent or chronic. continually buds off infectious particles. does NOT lyse the cell
explain how cells can be permissive or non-permissive in relation to viruses
permissive cells allow viral replication or integration
non-permissive cells allow entry but do NOT allow replication. they may be transformative
ABORTIVE = cell does not allow replication, but cell death still results due to the transformation (shape change)
step 1 of viral replication is ________.
explain how the virus accomplishes this
step 1 = target recognition and attachment
accomplished through viral attachment proteins (VAPs; spikes), host range, and tissue tropism
the second step of viral replication is ____.
explain how this is accomplished
PENETRATION
either through receptor mediated endocytosis or membrane fusion
what is VIROPEXIS
receptor-mediated endocytosis of a virus
explain how membrane fusion works
if the virus is enveloped, it can fuse with the host cell membrane and release the capsid into the cytoplasm
the 3rd step of viral replication is ____.
explain why this is done and how
uncoating
the virus removes it’s coat and the nucleic acid is delivered to the site of replication
in the SYNTHESIS of viruses, what 2 classes of gene products are needed?
early gene products — non-structural proteins that are required for REPLICATION
late gene products – structural proteins
true or false
membrane fusion is also known as viropexis
FALSE – it’s receptor mediated endocytosis
explain the difference in the process of viropexis vs membrane fusion
in membrane fusion, the virus has an envelope derived from the previous host cell. therefore, it fuses with the membrane of the next host cell and releases the nucleocapsid into the cytosol.
the plasma membrane is now continuous with the previous envelope of the virus
in viropexis, the enveloped virus recognizes receptors on the surface of the host and gets phagocytized in in an ENDOSOME with the virus still fully intact (along with the receptors that recognized the virus on the host cell surface).
the endosomal receptors then again recognize the VAPs on the virus within the endosome, which triggers the lowering of pH. the virus takes advantage of this and fuses with the endosomal membrane, and releases its nucleocapsid into the cytosol
which virus recognizes CR2 receptors on our cell surfaces?
Epstein-Barr virus
____ are potential viral receptors that are present on just about all of our cells
integrins
hepatitis A virus recognizes what receptor?
alpha 2 macroglobulin receptor
which 2 viruses recognizes CD4?
human herpes 7
HIV
which virus recognizes iCAM-1?
rhinoviruses
most DNA viruses generate ___ through ____
mRNA through SPLICING
TRUE OR FALSE
from the same DNA, MANY different mRNA transcripts are translated into proteins
TRUE
in a few viruses, the RNA genomes are arranged as….
what enzyme catalyzes this reaction?
individual segments. each segment encodes for a different (+)mRNA strand and thus a different protein
catalyzed by RNA dependent RNA polymerase which is ONLY present in viruses. the virus brings this enzyme into the host cell to accomplish (-) RNA genome –> (+)mRNAs
which RNA is the CODING STRAND
(+) mRNA
some viruses have one long genomic RNA strand. what happens with this?
this long genome can have multiple promotor regions which results in 3 different mRNAs and 3 different proteisn
viral replication can also occur….
through a polyprotein
there is a (+) RNA genome that goes through a NEGATIVE RNA INTERMEDIATE and then produces mRNA, to create a polyprotein that is cleaved by a protease to produce 3 mature proteins
WHY do viruses sometimes go through a (-) RNA intermediate ?
2 reasons:
-serve as a template to make many (+)mRNA strand (messages) to be packaged into the many newly formed viruses
-can make many many more mRNA to make many more viral proteins
ALL ROADS LEAD TO THE PRODUCTION OF ____
mRNA (+)
WHY do all roads lead to the production of mRNA?
need mRNA to make viral proteins for a successful infection
the synthesis of viral proteins requires what components?
host ribosomes
tRNA
post translational machinery (processing in golgi)
in regard to viral protein synthesis, what is happening at the host ribosome?
a giant, genome spanning polyprotein can produced which gets cleaved
can produce small transcripts that produce individual proteins
-produce smaller polypeptides
can human cells produce a polyprotein?
NO
this is an adaptation of viruses. they go through a (-) RNA intermediate to accomplish this
for humans, a single gene is a single transcript (mRNA)
In viral protein synthesis, they can achieve preferential translation over the host.
explain this
they block preexisting mRNAs, degrade host DNA and mRNA (so it has nucleotides to use), and decrease cellular transcription (no competition)
explain how viruses are able to assemble their proteins/nucleic acids to form a functional virus
they have recognition sequences that allow:
protein-protein
protein-nucleic acid
protein-membrane
interactions to fully form
to bud, viral membrane proteins (like VAPs) are inserted into the plasma membrane – in the region where the capsid will bud off. very convenient.
explain the release of newly formed viruses from the host cell
when released, the viruses take the membrane from the host so they become enveloped in the host membrane.
they can:
-bud from the plasma membrane
-bug through the ER/golgi (and remain intracellular)
-pass through the ER and be transported to the surface in endosomes
-they can lyse the cell
-form a cell-cell bridge
what does a virus make that enables the efficient release of a newly formed virus?
matrix protein – in a region with spike proteins on the INNER SURFACE of the plasma membrane
the nucleocapsid comes into that region of the plasma membrane of the host and gets pinched off along with the membrane to form a new enveloped virus
DNA viruses use ____ to make mRNA and use ____ to copy DNA
use DNA-dependant RNA polymerase to make mRNA
use freshly made DNA dependent DNA polymerase to copy their DNA
explain the entire process of DNA virus replication
DNA virus gets into the cell (either through viropexis or membrane fusion).
the DNA virus goes to the nucleus where it releases its viral DNA through a nuclear pore.
viral mRNA is then synthesized (using DNA dependant RNA polymerase of the host)
viral mRNA is then made to viral protein on a ribosome.
the proteins being made at this point are IMMEDIATE EARLY PROTEINS (non-structual proteins; required for replication of the virus)
then, EARLY PROTEIN SYNTHESIS and GENOME REPLICATION begins. at this point, DNA dependent DNA polymerase (JUST MADE BY THE VIRUS) is used to copy the viral DNA into multiple strands.
then late protein synthesis occurs (structural proteins)
packaging of DNA and capsid formation then occurs. this DNA containing naked capsid goes through the ER, and golgi.
gets into the golgi and buds off to get its membrane – becomes enveloped. get SPIKE PROTEINS in the golgi.
after leaving the golig, the newly formed active virus is either released and lyses the cell, exocytised and released, or released and directly put onto an adjacent cell
in viral DNA replication, where are we starting to package our newly made virus?
starts in the nucleus of the host. then moves through ER and golgi
explain the entire replication process of (+) RNA viruses
has VPg (viral protein gene) that binds to 5’ end of the message that helps to load messages. translation to polyprotein – cleaved – several proteins made right off bat
2 functions of - strand intermediate:
-make (+) mRNA to make more protein
-make (+)mRNA to be packaged into viral proteins
when the (+)mRNA is packaged into the viral proteins, it leaves the cell and lyses it
which viruses MUST carry RNA dependent RNA polymerase in order to successfully replicate?
(-) strand RNA viruses – they need to make a MESSAGE (+) mRNA
explain the process of (-)RNA replication
positive strand is made from the (-) RNA through RNA dependent RNA polymerase, brought in by the virus
this positive strand has 2 fates:
-transcribe back into negative strand which is needed for packaging – will meet up with structural proteins to form active virion
-directly used as mRNA to synthesize viral proteins
which replicates faster – viruses or bacteria?
viruses
which is more accurate by far – DNA polymerase or RNA polymerase?
DNA polymerase
viruses have terrible polymerases.
why is this a bad thing for us?
because this means the spike proteins of the virus are continually changing. therefore, the antibodies that we had previously developed against the virus are no longer effective
name 6 mutations that can occur in viruses that make it less strong of a virus
-lethal mutation
-deletion mutants
-plaque mutants
-host range mutants
-attenuated mutants
-conditional mutants
is there more recombination in DNA viruses or RNA viruses?
DNA
When HSV-1 and HSV-2 coinfect a cell, what happens?
recombination. this generates a hybrid molecule.
neither HSV-1 or HSV-2. BRAND NEW VIRUS
influenza has 8 separate strands of ssRNA.
if 2 strains infect the same organism, what can happen?
random assortment of those chromosomes to generate 2 very different viable viruses.
called ANTIGENIC SHIFT
can a virus with a lethal mutation be saved?
YES – by a wild type DNA fragment. recombination occurs to produce a viable virus.
this is called MARKER RESCUE
explain the process of antigenic DRIFT
a point mutation occurs.
as long as not a stop codon, it will only affect a SINGLE amino acid, most likely not a significant change. However, there can be a significant change that affects protein folding.
SLOW ACCUMULATION OF POINT MUTATIONS
explain the process of antigenic shift
2 strains of a virus infect the same organism and undergo a rapid random reassortment to produce completely unrecognizable viruses in some cases
more dangerous than antigenic drift. its a very fast process
