viruses Flashcards
all viruses are
obligate intracellular parasites
what does it mean to be an obligate intracellular parasite
cannot make ATP or proteins without using hosts’s parts
a full virus unit
virion
three parts of a virus
capsid
genome
accessories
capsid
protein coat around the outside of a virion
genome
the DNA or RNA a virus contains
accessories
envolelope (?), matrix, spikes and other stuff
viruses range in size from
10-400 nm
bacteria range in size
500-5000 nm
questions to ask to classify viruses by examining the genetic material they contain
- is it DNA or RNA
- single-stranded or double-stranded
- (+) sense or (-) sense
if genetic material is sense or positive sense
means that an mRNA sequence with the same sequence will code for a protein
if genetic material is antisense or negative sense
it means that a complementary mRNA sequence will code for a protein
grouping system based on examining the genetic material
Baltimore Classification system
Group I Baltimore classification
DNA (+/-)
Group II Baltimore classification
DNA (+)
Group III Baltimore classification
RNA (+/-)
Group IV Baltimore classification
RNA (+)
Group V Baltimore classification
RNA (-)
Group VI Baltimore classification
RNA (+)
Group VIII Baltimore classification
DNA (+/-)
2nd way to classify viruses
enveloped or naked
what is the viral envelope
phospholipid bilayer that surrounds the capsid
what does the viral capsid do when it exits the host
steal the membrane of the host cell to form the viral envelope
before the viral capsid exists host cells
they force the host to produce their own viral membrane proteins and put them in that membrane (that they will steal for their envelope)
the result of the viral envelope pathway
viral envelopes with host phospholipids but THE its VIRAL PROTEINS are made by the host’s ribosomes
soooooo viral capsid to enveloped virion
viral capsid takes some of host cell membrane that produced viral glycoproteins
pros for a virus containing a viral envelope
- does not need to kill host cells to spread
- cannot be fought off only with antibodies (harder to vaccinate)
cons for a virus containing a viral envelope
- sensitive
- requires a more complex genome to make envelope proteins
what are viral envelopes sensitive to
pH, temperature, drying out, heat
since viral envelopes are sensitive to pH, temperature, drying out, heat
cannot survive in GI tract or outside of body, sensitive to detergents
the life cycle of a virus
- attachment
- entry
- replication and protein synthesis
- assembly
- release
ATTACHMENT
virus recognizes and attaches to victim cell
ENTRY
virus (or virus parts) enters victim cell
REPLICATION AND PROTEIN SYNTHESIS
victim cell hijacked, makes viral DNA/RNA and proteins
ASSEMBLY
viral parts come together and make new viruses
RELEASE
new viruses exit the victim cell
Step 1: attachment is mediated by
envelope or capsid proteins called VAPs
VAPs
viral attachment proteins
there is usually what that a virus specifically targets
one specific surface protein or pattern that a virus
since there is usually one specific surface protein or pattern that a virus specifically targets
many viruses target just one specific tissue
step 1: attachment can be blocked by
antibodies…… so the immune system often tries to inhibit attachment
in step 2: entry, the
process is different depending on if the virus is enveloped or naked
entry naked
virus is taken through endocytes
entry enveloped
viral phospholipid bilayer fuses with host cell or virus is taken through endocytosis
in step 3: replication and protein synthesis
-DNA is “turned into” RNA in the nucleus (transcription)-RNA is “turned into” protein in a ribosome (translation
translation occurs
outside the nuckeus
depending on a viruses genetic materia, DNA/RNA replication can happen in many ways: if the virus has DNA
- the DNA must enter the nucleus to be copied into RNA before making proteins outside the nucleus (usually)
dna/Rna replication: if the virus has RNA
-If the virus has RNA, it may or may not need to be transcribed to a positive form, but does not need to enter the nucleus (usually)
unlike bacteria an eukaryotic cells, virsues
don’t replicate through division, instead new viruses are asembled
where are DNA viruses assembled
in the nucleus
where are RNA viruses assembled
in the cytoplasm
assembly enveloped viruses
produce some of their envelope proteins in the host’s membrane, which they plan to pull off with it later.
how do the parts of virus assembly know where to go
slight magnetic forces
step 5; release
virus levea host cell, different depending if its enveloped or naked
naked release
lysis: virus is copied many, many times inside, then invokes host cell “popping”.
enveloped virus release
lysis or budding, generally the host remains intact but part of the membrane is stolen
enveloped virus release
virus is copied inside, assembled, and released by “budding” off of the original host cell.
viruses can cause harm by inhibiting
host cellular DNA, RNA, or protein synthesis
viruses can cause harm by damaging
endosomes or lysosomes by releasing cutting enzymes
viruses can cause harm by adding
viral proteins to host cell membranes (autoimmunity)
viruses can cause harm because some
some viral proteins are toxic to host cells
a large buildup of viruses
inclusion bodies
viruses can cause harm because inclusion bodies
physically block cellular processes from haooenning
which damage is unique to retrovirus
chromosome damage , cancer causing mutation such as proto-oncogenes areunique to retrovirus
retrovirus
viruses that add their DNA to ours
types of viral infection
acute, chronic, latent, viruses can show different diseases at different stages
acute infection
you get the virus, you get sick a few days later, you die or beat the infection
chronic infection
you get sick, you may or may not show symptoms, you have the virus for a long time or forever
latent infection
you get the virus, you may or may not show symptoms, then there is a long delay before symptoms show again
how do we fight off viral infections
antibodies, type 1 MHC, interferons
to fight off viral infection, the antibodies we make
block most VAPs, and are most effective on naked viruses
MHC
membrane protein on all human cells
MHC is a form of
form of self-ID : Proteins destroyed by proteasome are dangled from the membrane and “sniffed” by WBCs
if proteins dangled from MHC are non-self
the cell is killed by WBCs
IFNs
interferons
interferons
a type of cytokine that cause all adjacent cells to turn on many anti virus genes
interferons signals uninfected
neighboring uninfected cells to destroy RNA and reduce protein synthesis
interferons signals infected
neighboring infected cells to undergo apoptosis
interferons activate
activate immune cells
