Class Four Flashcards
viruses are classified as..
obligate intracellular parasites
are viruses cells or living organisms
neither
how do viruses reproduce
by taking over the cellular machinery of their host cell
can viruses produce ATP
no - but some store it in their capsids (from their previous host)
all viruses possess..
a nucleic acid genome packaged in a protein shell
purpose of a virus’ protein shell
allows to convey the genome from one cell to infect other cells
a viral genome consists of..
DNA or RNA
single OR double stranded
linear OR circular
how many types of nucleic acids in a virus genome
only one
a factor that influences all virus genomes - limiting factor
size - viruses are super tiny
is the exterior protein shell of a virus rigid or flexible
rigid - cannot accommodate a larger genome
2 adaptions of viruses (size constraint)
only carry few genes (uses host proteins for transcription/translation/replication)
able to encode more than one protein in a given length of genome - uses more than one reading frame (genes overlap)
protein coat of viruses aka..
capsid
helical vs polyhedral capsids
helical = rod shaped
polyhedral = multisided geometric shapes
what do we use to classify viruses
their capsids
host for T4 bacteriophage
E.coli
where is the virus genome located
capsid head
what do the tail fibers and base plate do
attach to the surface of the host cell
how does virus sheath contract
using stored ATP - injects genome into host
viral capsid is composed of..
protein
viral genome is composed of..
nucleic acid (DNA or RNA)
where does the envelope around the capsid come from
derived from the membrane of the host cell
viruses that don’t have envelopes are..
naked viruses
what does an envelope contain
phospholipids/proteins/carbohydrates from host cell
+
proteins encoded by viral genome
why don’t plant cells have envelopes
they infect hosts with cell walls - no budding through the host cell membrane
2 ways viruses can be internalized
fusion with the plasma membrane OR
repeptor-mediated endocytosis
what is an early gene + example
group of genes immediately expressed after infection
hydrolase
what does hydrolase do right after infection
degrades the entire host genome
lysozyme is an example of a..
late gene
how are multiple copies of the phage genome produced
using the dNTPs resulting from the degradation of the host genome
function of lysozyme
destroys bacterial cell walls - all the produced viruses can escape
why is it important that lysozyme is a late gene
don’t want the host cell to lyse before the phage had time to replicate and assemble
first 2 steps of the bacteriophage life cycle
attachment/adsorption
penetration/eclipse
after the penetration step, viruses can enter..
the lytic or lysogenic cycles
what is a prophage
phage genome incorporated into the bacterial genome
what is the host called after prophage forms
lysogen
why are prophages dormant
transcription of phage genes is blocked by a phage-encoded repressor
lysogenic cycle - as host cell replicates..
so does the prophage
what type of viruses enter through endocytosis
animal viruses
what is endocytosis
a process where the host cell engulfs the virus + internalizes it
difference between lytic cycle and productive cycle
productive cycle is similar but does not destroy the host cell
what allows for the productive cycle
enveloped viruses exiting via budding and not lysis
(+) RNA viruses must..
encode RNA-dependent RNA pol (but don’t have to carry it)
what is a (+) RNA
a single stranded RNA which serves as mRNA
(-) RNA viruses must..
carry RNA-dependent pol (and encode it)
retroviruses must..
encode reverse transcriptase
3 main retroviral genes
gag: codes for viral capsid proteins
pol: polymerase codes for reverse transcriptase)
env: envelope codes for viral envelope proteins
double stranded DNA viruses often..
encode enzymes required for dNTP synthesis and DNA replication
what are subviral particles
infectious agents that are smaller and simpler than viruses
how do prions not follow the central dogma
they are self-replicating
how do prions affect normally folded proteins
comes into contact with them → prions act as a temple → protein is altered + becomes infectious
what is responsible for transmissible spongiform encephalopathies
prions
transmissible spongiform encephalopathies cause..
degeneration in the nervous system - holes in the brain
mad cow disease is caused by..
prions
why are prions hard to destroy
resistant to degradation by chemicals or heat
what is a viroid
short piece of circular, single stranded RNA - can base pair with itself
how do viroids work
hijack the cell’s DNA dependent RNA polymerase and directs it to read RNA templates
human disease linked to viroids
Hepatitis D
do viroids have capsids
no
who discovered cell theory
Robert Hooke
3 tenets of cell theory
all living organisms are composed of 1+ cells
cells are the monomer for any organism
new cells arise form pre-existing, living cells
main difference between prokaryotes and eukaryotes
prokaryotes do not contain membrane bound organelles - no nucleus
classification of living organisms aka
taxonomy
three domains of taxonomy
bacteria
archea
eukarya
3 eukaryotic kingdoms
animalia, plantae and fungi
prokaryotic genome is..
a single double stranded DNA chromosome
why does streptomycin only affect bacterial translation and not ours
structural differences in bacterial and eukaryotic ribosomes
what is the plasmid
circular piece of ds DNA - smaller than genome
encodes advantageous gene products
three shapes of bacteria
round (cocci)
rod-shaped (bacilli)
spiral-shaped (spirilla)
bacterial cell wall is composed of..
peptidoglycan
what is unique about peptidoglycan
has D-alanine (not found in animal cells)
what does lysozyme target
peptidoglycan
what happens when peptidoglycan is destroyed
cell becomes a protoplast - fragile and prone to lysis
gram pos vs gram neg
gram pos stains strongly
gram neg stains poorly
gram staining differs among..
2 different types of bacterial cell walls
gram positive bacterial walls have..
a thick peptidoglycan layer as its outermost layer
gram negative bacterial walls have..
thinner peptidoglycan layer with an outer layer with lipopolysaccharide
what is the periplasmic space
in gram neg bacteria
space between cell membrane and outer layer
what are endotoxins
found in the outer membrane of gram neg bacteria
not poisonous but cause our immune system to have extreme reactions (septic shock)
what are exotoxins
very toxic substances secreted by gram neg and gram pos bacteria
allows the bacteria to compete with other bacteria
what is the bacterial capsule
sticky layer of polysaccharide goo that surrounds the bacterial cell
makes it harder for the immune system to kill it
allows bacteria to stick to smooth surfaces (human GI tract)
how do bacteria move
with flagella
what is motile bacteria
bacteria with more than one flagella
monotrichous bacteria
one flagellum at one end
amphitrichous bacteria
flagellum at both ends
peritrichous bacteria
they have multiple flagella
3 major components of flagella
filament, hook and basal structure
purpose of the basal structure of flagella
anchors the flagellum to the bacteria
rotates the rod
rotation of rod (flagella) is powered by..
the diffusion of H+ down the proton gradient
chemoreceptors role in flagella movement
flagellar rotation occurs to move away from high conc of chemical
chemoreceptors transmits the signal to let the flagella know which way to rotate
what are pili
long projections on the bacterial surface (allows for attachment to other surfaces)
sex pilus
attaches male and female bacteria to form conjugation bridges
purpose of fimbriae
involved in adhering to surfaces
mesophiles
bacteria that favours mild temperatures (like humans)
thermophiles
bacteria that thrives in hot temperatures
psychrophiles
bacteria that thrives in low temperatures
autotrophs
bacteria that use CO2 as their carbon source
heterotrophs
rely on nutrients created by other organisms (glucose)
chemotrophs
get their energy from chemicals
phototrophs
get their energy from light
common medium for bacteria
agar
what is minimal medium
agar + glucose
bacterial lawn
dense growth of bacteria in a Petri dish
what is the doubling time
amount of time required for a population of bacteria to double its number
what is an auxotroph
bacteria that needs a molecule to live
requires an auxiliary trophic substance to live
needs to have this substance in their medium
bacteria which require oxygen are..
obligate aerobes
bacteria which don’t require oxygen are..
anaerobes
facultative, tolerant vs obligate anaerobes
facultative: will use oxygen if its there but don’t need it
tolerant: don’t use oxygen in their metabolism (indifferent)
obligate: poisoned by oxygen
how does bacteria reproduce
asexually
how does bacteria exchange information
through conjugation
4 phases of bacterial reproduction
lag phase
log phase
stationary phase
death phase
maximum population at stationary phase =
carrying capacity
what type of bacteria forms endospores
gram pos
when are endospores formed
in unfavourable conditions
structure of endospores
tough, thick external shells comprised of peptidoglycan
inside the spore: genome, ribosomes & RNA
3 ways bacteria acquires new genetic material
transduction
transformation
conjugation
what is bacterial transduction
transfer fo genomic DNA from one bacteria to another by a lysogneic phage
what is bacterial transformation
bacteria can internalize pure DNA in certain conditions
a key to bacterial conjugation
the F (fertility) factor
bacteria that has it = male
hows does a conjugation bridge form
male cell produces sex pili → contacts a female cell to form the conjugation bridge
F factor is replicated and goes to the female cell
a cell with the F factor integrated into its genome =
Hfr
high frequency of recombination cell
characteristics of archaea
live in very extreme conditions
single celled
reproduce via fission or budding
parasites and host cells
parasites cause damage to the host cell
symbiotic bacteria and host cells
they coexist
both cells benefit
+ RNA has to be able to code for..
RNA dependent RNA polymerase
(-) RNA must..
carry RNA dependent RNA polymerase and be able to code for it
problems with retroviruses
permanently in genome
rapid mutations
what shape is E. coli
bacillus
which gram is more antibiotic resistant
gram neg
has enzymes that degrade antibiotics in their periplasmic space
