Chapter 19: Genetics Of Viruses And Bacteria Flashcards
viruses are __ particles because
nonliving
not composed of cells
don’t replicate by themselves
do not carry out metabolism
a virus or its genetic material must be taken up by a living cell to
replicate
viruses are smaller than
size
bacteria
virus 0.02-0.4um
bacteria 1-5 um
eukaryotic cell 40-60um
Virus Host Range
Broad host range: can infect many different species and TMV: can infect 150 plant species
Narrow host range: very specific in which species/varieties the virus can infect
Bacteriophage phage: virus that infects bacteria
all viruses have
they don’t have
capsid: coat protein
genetic material: nucleic acid (dna or rna not both)
cells, cytoplasm, or organelles
+stranded RNA
- stranded RNA
retrovirus
acts as mRNA-> protein
template for mRNA -> +RNA -> protein
RNA acts as a template for DNA (RNA -> DNA)
types of single stranded rna
+ stranded RNA
- stranded RNA
retrovirus
virus genetic material
dsDNA
ssRNA
and some have ssDNA AND dsRNA
many animal viruses have a
viral envelope: membrane that surround capsid
viruses reproduce using the ___:
machinery
organelles, enzymes, energy
lambda phage
infects E. Colu bacteria dsDNA, complex capsid, no membrane
HIV
infects human helper T cells ssRNA retrovirus, capsid + envelope
steps in virus reproduction
attachment
entry
integration (lysogenic cycle)
synthesis of viral components-lytic
viral assembly-lytic
viral release -lytic
the virus reproductive cycles are
lysogenic- viral genome becomes integrated into host chromosome
lytic- virus enters cell and immediately begins to make new virus particles
lysogenic cycle: virus remains ___ in cell while’s its ___ into host cells dna
latent = inactive
incorporated
pro virus are in ___ cycle
lysogenic
lysogenic cycle: virus goes through a __
viral dna is __
anything made?
dormant period
replicated everytime the cells dna is replicated
no new virus particles are made at this time
lytic cycle: virus enters cell and ___
integrated?
lysogenic?
immediately makes new virus particles
viral dna may not be integrated into host chromosome
or lysogenic cycle may be very short
lifecycle of lambda phage: 1st step
attachment to host cell: protein in tail fibers attaches to proteins on surface of bacterium, in outer bacterial membrane
lifecycle of lambda phage: 2nd step
entry: lambda phage injects DNA into cell
capsid never enters the cell but hangs out in the outside
dormant
active
lysogenic
lytic
lifecycle of lambda phage: 3rd step
integration: phage DNA is integrated into bacterial DNA using enzyme integrase
everytime the ___ cell replicates its dna the __ is also replicated
Bacterial
Viral
no new viruses are made during the
lysogenic cycle
at the end of the lysogenic cycle viral dna is
excised from the bacterial DNA
what controls whether a virus enters lysogenic or lytic cycle
environmental factors
lytic cycle: 1st step
synthesis of viral components:
new viral protein and DNA are made
viral DNA is circularized
bacterial DNA is degraded
lytic cycle: 2nd step
assembly of new virus particles:
viral DNA packed inside capsid
lytic cycle: 3rd step
release:
viral enzyme lysozyme digests bacterial cell wall
bacterial cell lyses= bursts open
new virus particles are released
how do you count phage?
plaque assay:
plate bacteria in petrified plate to grow a solid layer of bacteria = lawn
some bacteria cells are infected with phage = virus
phage will kill off bacteria and produce clear areas = plaques = circle of death
HIV lifecycle: 1st step
attachment to host cell:
spike glycogen proteins in viral envelope bind to receptors on pm of helper T cells
HIV lifecycle: 2nd step
entry:
viral envelope doses with pm of host cell
capsid enter cells
uncaring: cellular enzymes digests coat proteins
viral enzymes and RNA released into cytoplasm
HIV lifecycle: 3rd step
integration: lysogenic
viral RNA is reverse transcribed to make a dsDNA copy using reverse transcriptase (reverse transcription- RNA make DNA copy)
viral is integrated into host chromosome by enzyme integrase
provirus may be latent for a long period - dormant (not making anything viral so hard to know if you have it)
HIV lifestyle: 4th step
synthesis of viral components- lytic begins
new viral RNA and proteins are made
spike glycoproteins inserted into pm
HIV lifestyle: 5th step
viral assembly
new virus particles: capsid protein
2 molecules RNA and 2 molecules reverse transcriptase
capsid assembles with spike glycoproteins during budding
2 stage assembly of HIV
capsid proteins assemble around
2 molecules HIV RNA
2 molecules reverse transcriptase
HIV lifestyle: 6th step
release:
Virus buds from host cell
virus gains envelope during budding
cell sheds virus particles without being killed
enveloped viruses are released by
budding- most envied animal viruses do not kill the host cell as they are released
latency - dormant occurs in 2 ways:
virus becomes integrated into host DNA (ex HIV)
virus exists as an episome (genetic material element that replicates in cell independently from chromosomes, like plasmid)
sometimes virus can also integrate into chromosome
herpes simplex virus type 1:
herpes simplex virus type 2:
varicella zoster:
cold sores
genital herpes
chicken pox
Latency: varicella zoster
initial:
second:
chicken pox- virus may remain latent as episome for years
shingles- when virus shifts from latent to lytic cycle it changes
Viruses: H=
N=
hemaglutinin- binds to host cell
neuraminidas- helps initiate infection
influenza is a ___ virus
respiratory
Flu vaccine production
1) CDC predicts which flu strains will be the most common in the next year
2) injections these flu viruses into eggs to make vaccine (kill virus particles, screen to make sure vaccine works, takes 6 months)
3) construct trivalent or quadivalent (protects against 4 types) flu vaccine and distribute
a vaccine __ the immune system and greatly ___. It is not ___
primes
greatly decreases the chance of infection
a cure for an existing infection
vaccine can eliminate ___ before___
virus and virus infected cells
full blown disease develops
swine flu:
bird flu:
H1N1, 2009
H7N9, 2013
which influenza is most worried about
H1N1- can cause an epidemic
does every animal have a flu virus?
yes
is it hard for humans to get bird flu?
swine flu?
yes
no
mixing of proteins from different virus strains occurs in
pigs
epidemic
new flu virus with proteins not normally found in human flu strains made -> no immunity-> epidemic
how do viruses become pandemics?
reassortment- mixing of genetic material from two strains in one host
it mutates very wuickly
emerging viruses
viruses or strains of viruses that have arisen recently
more likely to cause disease epidemics
new strands are caused by mutations
viral replicase lacks proofreading
new viruses may be derived from animals and only recently gained the ability to infect humans (change in host range)
Origination of new virus
reassortment
mutation
change in host range
spread of virus - small isolated population to the rest of the world (air travel)
mutation: viral replication is error prone because
new forms of virus may infect individuals who were
no proofreading
immune to old virus strain
hantavirus:
bird flu:
COVID 19:
from rodents, deer mice
from chickens, pigeons
from bats, pangolins
most worried form of virus spreading
human to human- epidemic
animal -> animal
animal-> human
human-> human
SARS
severe acute respiratory syndrome
southern china 2002-2003
may have originated in bats
gained ability to infect humans and livestock
type of coronavirus
Viruses are grouped into families based on
their structure and life cycle
some Covid causes
others cause
mild infections in humans- common cold
severe infections: sars, mers, covid 19
Covid 19 structure
genome + stranded rna molecule
capsid: N protein surround the rna
envelope membrane with spike glycoprotein (s) and other proteins (m,h,e)
sense strand
antisense strand
+ stranded
- stranded
what is the first protein to be made from + stranded rna
replicase (needed to make more copies of viral RNA)
genomic rna
the entire rna molecule found in the virus particle
in Covid 19 the genomic rna is a very long mRNA with a 5’ cap and a poly A tail
sub genomic
shorter mRNAs made form the genomic rna
they are used to make other viral proteins
Covid 19 replication process
Attachment: uses spike glycoproteins to bind to receptor on cells
entry: viral envelope fuses with pm of cell
uncoating: capsid protein is removed, release +rna into cytoplasm
viral rna is used as mRNA
make replicase enzyme
replicase makes + into -rna
