Intro To Prokaryotes #2 Flashcards
from archaea onwards
what are the 3 broad groups of archaea?
- Methanogens (produce methane)
- Halophiles (salt loving)
- Thermophiles (heat loving)
how do archaeal cell envelopes differ from bacterial envelopes? (4)
- s layer may be only component outside plasma membrane
- some lack a cell wall
- capsules & slime layers rare
- lack peptidoglycan
- s layer may be outside membrane separated by pseudomurein
what feature of the cell wall in archaea make them not susceptible to certain antibiotics (2)
no peptidoglycan so not susceptible to lysozyme, beta-lactam or glycopeptide antibiotics
what are some key features of archaeal membranes? (5)
- have distinct membrane lipids (diff from bacteria & euks)
- branched chain hydrocs (alkyl isoprenoids) bonded to glycerol by ether bonds, not FAs linked by ester bonds
- contain diglycerol tetraethers (not in bacteria or euks)
- some have monolayer structure instead of bilayer (due to diglycerol ethers)
what evidence is there that archaea are in a distinct group and are not eukaryotes or bacteria ?
contain diglycerol tetraethers
have distinctive membrane lipids
(not in bacteria or euks)
how does pseudo murein differ from peptidoglycan (3)
- contains L-aa rather than D-aa;
- has β(1-3) glycosidic bonds and not β(1-4) glycosidic bonds
- contains NAT & NAG not NAM & NAG
what are archaeal chromosomes like?
similar to eubacteria, single closed DNA circle per cell
what do archaeal ribosomes have in common with bacteria?
ribosomes are 70S but shape is variable
what is the protein synthesis of archaea sensitive and resistant to?
- sensitive to anisomycin
- resistant to chloramphenicol and kanamycin (like euks)
aniso affects archaea
chlorine and kites resistant to archaea
what is the EF-2 (elongation factor) in archaea sensitive to?
diphtheria toxin (like euks)
archaea elongates dippy (dipper)
drugs
in what way is archaeal rna polymerase similar to that in eukaryotes?
insensitive to rifampicin and streptolydigin (usually inhibit bacterial transcription)
drugs
what effect does streptolydigin have on prokaryotes?
bacteria: inhibit transcription
archaea: rna polymerase insensitive to streptolydigin
archaea like eukaryotes
drugs
what effect does rifampicin have on prokaryotes?
bacteria: inhibit transcription
archaea: rna polymerase insensitive to rifampicin
archaea like eukaryotes
how is the small subunit rrna in archaea similar to bacterial (1)
is 16S and similar in length to bacteria
which group was archaea more closely related to upon phylogenetic analysis?
eukaryotes
what reasons are there to consider archaea prokaryotic ? (4)
- similar cell sizes to bacteria
- no nuclear membrane & cellular organelles
- possess single, large, circular chromo
- may have plasmids
what is a protoplast ?
plasma membrane & everything within it
what are plasmids? (2)
- extrachromosomal DNA found in bacteria, archaea, some fungi
- usually small, closed circular DNA molecules
what are episomes ?
a type of plasmid that may integrate into chromosome
what is curing ?
the loss of a plasmid
what is refractive index?
a measure of how greatly a substance slows the velocity of light
focal point ? (F)
the specific place where lenses focus light rays at
focal length (f) ?
the distance between centre of lens & focal point
what does a short focal length mean?
more magnification
what does a bright-field microscope do?
produces a dark image against a brighter background
what is resolution ?
ability of a lens to separate (distinguish) small objects that are close together
what is the relationship between wavelength of light and resolution?
shorter wavelength → greater resolution
what is the numerical aperture ?
ability of the lens to gather light (n sin θ)
what two factors is numerical aperture determined by?
- refractive index of the medium
- theta (1/2 the angle of the cone of light entering the objective lens)
can any lens working in air have a numerical aperture greater than 1.0 ?
no, because air has a refractive index of 1.0
how to increase numerical aperture in air ?
increase n by changing the medium in which the objective lens works from air to immersion oil
what is the working distance ?
the distance between the front surface of lens & the surface of cover glass or specimen when it’s in sharp focus
what is heat fixation ?
routine use with bacteria & archaea
preserves overall morphology but not internal structures
what is chemical fixation ?
used with larger, more delicate organisms
protects fine cellular substructure & morphology
what are chromophore groups ?
chemical groups with conjugated double bonds and gives dye its colour
what is differential staining used for ?
to detect presence or absence of structures (e.g. gram staining)
what causes the colour change in gram staining?
shrinkage of pores of thick peptidoglycan layer of gram-positive cells prevents loss of crystal violet during decolourisation step
what is the terminus ?
site at which replication is terminated
located opposite of origin
what is the replisome ?
group of proteins needed for DNA synthesis
what is the growth curve?
- observed when microorgs are cultivated in batch culture (in closed vessel w single batch of medium),
- plotted as log of cell nr vs time
what are the four distinct phases of the growth curve ?
- lag
- exponential
- stationary
- death
explain the lag phase in the growth curve (2)
during this phase, cells are synthesising new components to replenish spent materials and adapt to the new medium
describe the exponential phase in the growth curve (3)
- rate of growth & division is constant & maximal,
- cell pop is most uniform in terms of chemical & physical properties during this phase,
- cells exhibit balanced growth
(aka log phase)
what is balanced growth ?
cellular constituents are manufactured at constant rates relative to each other
under what conditions does unbalanced growth occur?
-
change in nutrient levels
shift up = poor to rich medium
shift down = rich to poor medium - change in env conditions
describe the stationary phase in the growth curve (3)
- pop growth eventually ceases & total nr of viable cells remains constant
- active cells stop reproducing or reproductive rate is balanced by cell death rate
what are possible reasons for the stationary phase ? (4)
- nutrient limitation
- limited oxygen availability
- toxic waste accumulation
- critical pop density reached
what are the two alternative hypotheses for the senescence and death phase in the growth curve ?
- cells are temporarily unable to grow (viable but not culturable VBNC) = cells are alive but dormant, capable of new growth when conditions are right
- programmed cell death (fraction of the pop genetically programmed to die i.e. commit suicide)
