Topic 5: the cell wall/cell envelop Flashcards
What is the cell wall
rigid structure that lies outside the plasma membrane
What gives gram psotive cell wall the negative charge
techoic acid
What gives gram negative cell walls its negative charge
Lipopolyscharride’s fatty acids
What does the cell wall of gram positve contain
- peptidoglycan
teichoic acid
lipotechoci acid (embreeded into the plasma membrnae)
proteins: porins (theres less in gram positive)
What does the periplasm of gram positive cells contain
- contains hydrolytic enzyme for nutrient acquision: phosphatase,s nucleases
- contains accessory proteins for membrane transport and secretion
- contains enzymes involved in the sysntehiss of peptidoglycan and other cell wall coponents
- may often cntain enzymes for inactivation of anitbiotics
not as prominanent as gram negative cells (which have 2 layers)
What does the plasma membrane of gram positive cells have
contain major compoennts of transprot and export.
cjttajisn most of the compoennts of chemotaixs (flagella)
cell wall of gram negative cell envelope. Inner leaflet and outer leaflet
outer memerbane:
outer leaflet: lipopolysaccharide (LPS)
- inner leaflet: phospholipid and lipoprotein (lpr)
- proteins: specific and nonspecific porins as well as others
peptidoglycan of gram negative cell wall
loosely associated with cytoplasmic face of the inner leaflet and suspendd in the periplasm
What does the peridpasl of gram negative cell have
peptidoglycan
- contains accessory proteins for membrane transport and secretion
- contains enzymes involved in the sysntehiss of peptidoglycan and other cell wall coponent
Plasma membrnae of gram negative
transport systems
a
chemotaxis systems
What does the cell envelop refer to
the cell wall, perisplami, pus the plasma membrane: is due to similar lipid bilayer of outer and inner membrane
Gram negative vs gram positive cells
- outer memrbane and peptidoglycan is suspended in the periplasm.
- gram positive: peptidoglycan/teichoic acid is external to the periplasm.
if an antibiotic targets peptidoglycan, there would be a greater effect on
gram positive celsl
where are adhesins found
in the teichoic aicds, lipoteichoic acids in gram postive, and other cell surfaces such as fimbriae, capsules
What are some functions of cell walls
- maintain shape and integrity (without it cells lyse easily)
- involved in cell division - transverse septum
- contribute to pathogenitiy and plays major role in adhesiveness.
adhesions are foiund in the cell wall (teichoic acid, lipoteichoic acid) - protect cell from toxic substances/modulate what enters and leaves the celll
What are the basis of action of beta lactam antibitoics
removing cell wall -> bacteria lyse easily. penicillin and cephalosporin
why is the abilityt to stick to materials/other tisuses important
for nutrient acquision and colonization
the ability to adhere requires
adhesions on the bacterial cell wall surface and specific adhesion receptors on the target tissue
Virulence factors of the cell wall:
- adhesions
- porins: affect entry and exit of certain toxins
How do the porins protect the bacteria
cell wall + plasma membrane modules what enters and leaves the cell. cell walls contain specific and nonspecific porins.
modules the entry and exit of certain toxins
What is the lamb protein
protein embedded into the outer membrnae, brings in sugars. its what the bacteriophage T4 in e. coli binds onto.
if you lose the recpeotor -> cant survive if u wanna be insensistive to bacteriophage lmabda
Whats an antigen
is an immunogenic substance, which can be a protein, polyscarride or other cell substance capable of stimulating the immune system of an animal -> produces a specific antibody against the antigen. antibodies interact specifically with the antigens that induce their synthesis.
What are some other functions of cell walls
- contain receptor sites of certain bacteriophages
receptor for bacteriophage lambda: outer mmembrane - determines the stanining charactisris of bacterial cell:
+ gram neg/gram psotive, acid fast -> diagnosis of bacterial diseases - immunitenicity: along with cell surface components such as flagella, capsules, pili -> stimulate antibiody synthesis in the host
Immunogen? immunogenic
refer to antigens. Immunogen: substances able to induce an immune response
whats an antibody
a specific protein by the aminals immune system. response to a specific immunogen
Whats the basis of vaccines
antibodies against bacterial cell wall or other bacterial, viral, fungal or protozoa antigens
What do antibodies against bacterial cell wall or other adhesins do
they can inhibit bacterial adhereance,
colonization is dependent on adherance, these antibiodies are effective in preventing infection.
What are exceptions to prokayrotic cell walls which arnt + or -
mycoplasma: lack cell wall
acid fast bacteria: have a modifieid positive type of cell wall
archaebacteria: unusual cell wall that are neither gram negative or positve
if a bacteria loses its cell wall, it wont die if
it forms a biofilm
whats a biofilm
bacteria that has lost its cell wall -> stablized in a polyscaharide layer
What are the 2 types of mycoplasma
- L -form
- and mycoplasma genera
What is the L-form
Cells that normally have cell walls but have lost their cell walls due to
- mutations in cell wall synthesis
- presence of antibiotics that inhibit cell wall synthesis: beta lactam anitbiotics
- presence of enzymes that can degrade bacterial cell walls
- L forms do not represent a particular taxonomic group
some facts about the genus mycoplasma
- extremely small
- sterols in their plasma membrane like eukaryotes (to maintain membrane fluidity)
- pleomorphic: due to lack of cell wall
- osmotically fragile: lyse unless protected iin specifcal media such as serum
- difficult to grow in culture
Where do mycoplasma grow
in serum
how is the presecne of mycoplasma usually determined
by PCR or fluorescent anitbodi
What are some important mycoplasma pathogens
- mycoplasma pneumonia: causes “atypical pneumonia” - atypical compared to streptococcus pneumoniae: common cause of bacterial penumonia in children
- ureaplasma ureticulum: prsent in urogenital tract, sexually transmited, cause of inferiltiy: beta lactam antibiotics cant inhibt the growth of these but tetracyclin, ciprofolxin can..
Where are heat shock proteins found
in human mitochondria and cytoplasm
What does Mycobacterium leprae do?
causative agent of leprosy -> creates an autoimmune disease
hyposthesis of the etiologoy of autoimmune form of leprooy
- the infected person makes antibiodies against M. leprase heat shock proteins
the bacteria makes heat shock proteins (hsp60)
our body makes antibiodies against bacterial Hsp60 , which cross react with human hsp60
high levels of both bacterial and human hsp60 are produced duirng rpeated feverd s-> resulting in antigen/antibody reaction
How can M. leprase infection be cured
with antibiotics. but the autoimmune disease and tissue desctruoon cannot
bc m. leprae is acid fast it can intensify the problem bc
mycholic acid -> its like an adjuvant and can boost the immune response
What are adjuvants
substanes that enhance the rate of formation and quantity of antibiodies.
may not be immunogenic on its onw.
if mixed with anitgen -> stronger immue response produced by aminal
acid fast cell walls are good adjuvants
Whats a common adjuvant
Freunds complete adjuvant
What is mycholic acid
rich in acid fast cell walls, a complex fatty acid
What are treamtnets to tuberculosis
isoniazid (antimetabolite - competitve inhibitor) and antibotic rifampin
In the acid fast procedure, what takes place of iodine in the gram stain
machanlite green (its a mordant for the gram stain, and uses heat drive in)
almost all bacteria except .. have either a gram psitive or gram negative cell wall
except mycoplasma, acid fast bacteria and archaebacteira.
almost every clinical diagnosis begins with a gram stain
archaebacteira are affected by beta lactam antbiotics or are broken down by enzymes such as lysozyme?
No
Which types of archaebacteira lack cell walls
thermoacidophiles
lack cell wall but plasma membrane is strengthened by usual lipids call diglyerol-tetraeitehrs, by lipopolysachcarides, glycoproteins
Some archaebacteria stain as if they are gram + or gram -, however
thye contain unsual types of polymers:
gram +: cotnain pseudomurein: resembles peptidoglycan
gram neg: have a thick layer of protein or glycoprtein outsid ehte plasma membrane
do gram neg have teichoic acid?
no
do gram +have LPs and LPr
no
Characteristic of cell wall found in gram negative and gram + bacteria provide
the perfect target which only affects killing of the bacteria
How unique is peptidoglycan
very unique to bacteria cells
where are teichoic acid, LPs, LPr found
primarkily in bacteria. variation in LPs and teichnoic acid -> identification of different speices or strains
Structure of peptidoglycan subunit
glycan strand and tetrapeptide strand
Glycan strand: N-acetymuramic acid and N-acetyl glucosamine (NAG): linked by 1,4 glycosidic linkages
Tetrapeptide strand attaches to the NAM stem petide with 4 aminoa cids.
variation in positon 3 -> virulence difference.
peptide interbridge connects the stem peptides. in gram negative, joined directly (3rd aa is linked to the 4th aa)
What does the meshwork provide
confers a particular shape and rigid structure to the bacterial cell.
How is amino acid 3 in gram negative cell walls can be a antimetbaolite tareget
aa 3 is meso-DAP - intermeiate in lysine biosyntehtic pathway but not an intermediaete in mammalian lysine biosyntehsis
-> could be a possible target for antimetabolite or antibiotic
Gram positive cell walls aa 3
more variaiton, usually an intermdiate of lysine boosysntheies. is species specififc
Variation in amino acid 3 makes a
virulence diffence
loser murein meshwork in gram positive is due to
prescence of bridge between adjacent step peptitsd
how doe differences in murein chemistry affect virulences of the bacterial cell
changes to the adhesiveness (in gram positive cells more) -> changes in sensiy
how do hypertonic solutions kill bacteria and fungi that would otherwise spoil the food
some bacteria cannot grow in high salt/high sugar.
some fungi can grow at higher sugar ocncentrations
What are autolysins
they carry out limited digestion of peptidoglycan. provide aceptor ends for addition of new peptidoglycan units. used in cell wall growth
How do autolysisns help cell wall grow?
small openings in the exisitng cell wall. new cell wall can be laid down in between. process requiers FTs proteins that interact at the septum. similar to tublin
How do division between cocci and rod differe
rodd: spechial hemisphere formation
rod (rare): pole formation
rod (common): side wall elongation
How do autolysins work
they break down the peptide in between and the stem peptide
What are some methods of antibiotic resistance
- Enzymatic inactivation
- modified target
- resistance conferring plasmid
- modified cell wall and membrane
- efflux pumps overexpression
where is beta lactamase located
in the periplasm or secreted from resistant cells
How does beta lactam antibiotics effect the cell
Enters the bacteria cell through pores in the outer membrnae (gram negative).
or permeate directly through the gram positive cell wall.
prevents PBP from catalyzing corss linking of subunits -> weakens -> more free subunits -> unstable -> autolytic enzymes making cells lyse
beta lactam antibiotics only affects
growing bacteria
why are beta lactam antibiotics considered competitve inhiitors
transpeptiases = penicilin binding protein
beta lactam antibiotics is similar to the normal substrate of PBP (transpeptidase) -> competitive inhibitors
What is the hypersensitiy to beta lactam antibiotics
beta lactam antibioics have high selective toxicity -> allergic reaction
