chapter 6 Flashcards
virus
obligate intracellular parasite
-can only exist and replicate in a host cell
-specific for host and infect all froms of life
-no animals are immune
-ultramicroscopic
-dont fullfill characteristics of life
-not cellular in nature
characteristics of life
-cellular organized
-reproduction
-metabolism
-heredity
-responsiveness
-growth/ develop
-homeostasis
-are they alive? only rlly in presence of host cell
virus genome
-dna or rna never both
-single or double stranded
-have been around since life
can viruses synthesize proteins
no because they lack ribosomes
-some exceptions
what microscrope can we use for virus
electron microscope
-most under .2 microns
virus evoluton
virus only carry the genes they need to infect a host cell
virus structure
-capsids
capsides
-repetitive subunits of proteins/ capsomers
-protein coats that enclose and protect their nucleic acid/ genetic material
-helps deliver genetic material to host cell
-some are surrounding in envelope/ phospholipid bilayer
-helical or iscosahedral
no envelope
naked virus
envelope
the outside layer that touchs the host cell
helical capsid
-capsides in cylinder and the genetic material is wrapped around the cylinder
-naked helical viruses are not human pathogens
icosahedral capsid
-20 sides and 12 corners
-1 or multiple proteins to make capsid
-densely packed and can form crystals
-easier to use xray rystallography to get an image of it
viral envelope
-mostly viruses that infect animals
-gets envelope when it leaves host cell
-spikes are exposed proteins outside the envelope they help attach to host cell
-
surface proteins of envelope
help your immune system recognize the pathogen
nucleases
the enzyme that would degrade viruses without the capsid present
-on our hands etc
complex viruses
-atypical
-no capside
-ex: poxviruses: covered in dense layer of lipoproteins, have a large genome and structure
-ex: bacteriophage that have a polyhedral nucleocapsid, helical tail and attachment fibers (alien)
viral dna
-circular or linear
viral rna
-single or double strand
-multiple pieces (pizza that is cut in 8 slices)
-ssRNA (positive sense) or negative sense
positive sense rna
rna read by ribosome and translates d into aino acids to make proteins
-rna that foes to ribosome immediatly and the proteins make sense
negative sense
-genome if it were to go through ribosome would make a nonsense protein because it is the complimentary strand
-needs to be converted to sense before it is transcribed
in the capsid there are
viral proteins that the virus needs to replicate, polymerases, reverse transcriptase (to synth DNA from rna/ aids), RNA dependant rna polymerase (uses RNA to make new RNA) in negative sense, positive doesnt rlly need it
viral classification
-family name ends in viridae
-genus: virus
-7 orders, 96 families and 350 genera of viruses
-simple: Herpes simplex 1
absorption
virus encountering host cell
-endocytosis or fusion
-endo is used by naked cells
-fusion is for enevelope viruses: phospholipid bilayer or viruse fuses with host cell bilayer bc proteins in virus envelope help mediate this process (fusogenic proteins) draw the membranes together
-
penetration
virus taken into vesicle
uncoated
-genome leaving capside, vesicle etc
synthesis
new genome, proteins, capsides etc
assembly
-proteins inserted into cell membrane for the viral envelope
release
budding of vesicle
-takes envelop from lipid bilayer
-budding
host range/ tropism
-cell or tissue type the organism can infect
-ex: polio infects intestine and motor neurons
why does DNA virus go to nucleus
-dna and rna polymerase
-many will use host cells dna and rna polymerase which is in the nucleus
-replicating in cytoplasm it can used enzymes we have
-RNA viruses dont need the polymerase so they will reproduce in cytoplasm
lysis
nonenvelpped and complex viruses released when cell dies and ruptures
virion
-fully formed extracellular cirus particle that is cirulent and able to establish infection in a host cell
-not defective and can infect a host
cytopathic effects
-virus induced damage on cells
-change in size or shape
-sytoplasmic inclusion bodies (masses of virus particles or damaged cell organelles)
-fusion forms multinucleated cells (syncytia)
-cell lysis
-alter DNA
-transform cells into cancerous cells
persistent infections
-cell harbors virus and cell is not immediatly lysed/ killed
-length of time varies, weeks or years
-periodic reactivity: chronic latent state (mono/ measles hiding in the brain eventually lethal, chicken pox and shingles)
transformation cell
-virus turning cell cancerous
-result of altering genetic material bc this alters their normal rules (multiple uncontrolled, cells dont die)
-HPV
-Epstein barr and malaria
bacteriophages/ phages
-infect viruses
-infect ecoli
-remains out of cell and injects DNA into cell
-lytic cyles
lytic cyle
-phage recognizes surface features
-bacteria injects genome
-murders host cell
-genome hijacks cell processes and uses it to replicate phages
-protein will weaken cell wall which will burts open destroying host and creating phages
temperate phages
can do lysogenic cylce
prophage
genome inserts but the cell is not lysed
lysogeny
prophage is retianes and copies during normal cell division which transfers the temperate phase genome to all host cell progeny
induction
activation ogf lysogenic prophage
-host is killing itself to take phage with it so phage kills it first
viruses with toxins
-get thos etoxins from bacteriophages and those toxins can infect humans
-lysogenic conversions
culture a virus
-needs to culture host bc they are intracellular parasites
-easiest is a cell culture that support the virus
-bird embryos are eggs that we inject the virus through the shell (flu)
-live animal inoculation only when necessary
plaque assay
measures ability of virus
-purple cells and observe how the infected cells die, the clearing/ plaque tells us where the virus kills the cells
how to detect animal viruses
-too small to stain or microscope
-symptoms can help bc many viruses can cause similar symptoms (ex: flu like symptoms)
-pcr (detecting gemone)
-immunoflouresance/ em
-look for part of virus (rapid covid test which binds to the capsid of the covid)
-look for anitbodies in immune system (used post infection)
treating viral infection
-antiviral drugs have bad side effects (will target host cell too) (ex: AZT for HIV also targets nucleic acid synth: nucleotide analog)
-antibiotics don’t work
-vaccination is best
satellite virus
dependent on other virus replication
-replicate only in the cells infected with adenovirus
-delta agent (like hepatitis) but it needs hepaatitis to replicate
prions
-infectious protein that are misfolded and they have no nucleic acids
-one misfolded protein that infects the other
-resistant to sterilization techniques
-cause spongiform encephalopathies / fatal neurodegenerative disease
-common in animals: scapies (sheep), bovine spongiform (mad cow), wasting disease (elk), and creutzfeldt jakob (humans)
virus origins
many come from humans, some zoonotic
chronic infection
-chronically producing new viruses
-slow rate
-symptoms could be absent
latent infection
-chronic virus that spikes up and becomes acute but then goes dormant
-herpes
oncogenic virus
causes cancer by bringing an ocogene
-accidently activate oongogene
-uncontollwed growth
teratogenic
can cross placenta and infect fetus
covid
-enveloped, nonsegmented positive sense RNA virus (large genome)
-spherical virions
-disease in mammals and birds
-some forms infect people sars 2
sars covid 2
-entry: envelope fuses to plasma membrane or endocytosis into endosome
-positive sense rna gemone single stranded (nucleic acids that can make genes/ proteins =ORF)
-ORF makes initial proteins that the virus uses to take over cell
-primary translation/ polyprotein procesisng to make first viral protiens
-new rna genome copies
-OFS make compartments in ER (DMV) which protects genome replication from immune bc it needs to make a double strand to duplicate which the cell would attack
-uses compartments to make genome
-DMV parts are packaged and sent to er golgi complex to form where it gets spike proteins
-leaves through exocytosis
late stage of virus
making structrral proteins/ parts of the virus
nsp
non structural protein
-covid makes all proteins at once and then protease will cut it at the subunits to make them individual proteins w diff funcitons
dmv
double membrane vessicle
-covid uses rtc to make genome (RNA)
RTC
replication transcription complex
rna cap
lets ribosome bind to it to make proteins
-pink cap on the end of the rtc
-starts translation bc positive sense and cap lets it
-hard to get for viruses so diff method for diff viruses
passing stop codon
-happens less
-fram shift is a way to control how much protein we are producing that is NSP 12, 13, 14 , 15, 16
-more small nsp bc the knot in the RNA does not cause frame shift and the stop codonis read
subgenomic rna
all about helping the genes get caps
-genes that make virus structural proteins
-5 prime end cap on RNA that is needed for ribosome translation inititation
RBD
receptor binding domain
three flues
A B C
-A is most serious and causes most infections
-based on ribonucleoprotien antigens
-enveloped
-negative sense
Flu entering cell
three types of proteins inserted into lipid bilayer (hemagglucinin, neuraminidase and M2 ion channel protein
flu viral ssRNA is
surrounded by nucleoproteins and needs RNA transcriptase
-8 segmentes of ribonucleoprotein
-needs all 8 to infect
-10 genes encoded in the 8
flu replication
attaches to respiratory cells and segments of RNA enter the nucleus
-virus budds out of cell when done
-positive sense genome makes more negative genome and makes viral proteinsfl
flu positive rna
intermediary for proteins and rna
flu glycoproteins
-make the spikes
-hemagglutinin
-nueraminidase
hemaglutinning (H)
15 subtypes
-most important virulence factor and lets it bind to host cell
nueraminidase (N)
9 types
-hydroluzes mucus and assists in viral release/ budding
antigenic drift
constant mutation
-flu makes lots of mistakes which makes mutation
-changes amino acid composition (minor change)
antigenic shift
-influenza A bc muliple strains infect same cell
-oneof the genes or RNA is substituted with a gene or stranad from another influenza virus from diff host
-huge change
-pizza box: one slice burd flue one slice pig flue etc
