Bacterial Cell Envelope Flashcards
what are the 3 major components of most bacterial envelopes
plasma membrane, peptidoglycan and envelope proteins
what are the key differences between gram pos and neg
gram pos: thick peptidoglycan layer, single membrane, lipotechoic and techoic acid polymers
gram neg: thin peptidoglycan layer, inner and outer membranes, LPS (endotoxins) surface polymer
what are the features of a mycobacterial envelope
thin peptidoglycan layer, single membrane, mycolic acid layer (hydrophobic). has arabinogalactan which links peptidolgycan and mycolic acids
what are the features of a wall-less bac envelope
no peptidoglycan and must live in osmotically balanced environment
what are the chemicals used in gram stain
crystal violet, iodine, ethyl alcohol, safranin
how does the ziehl nielsen stain work
mycolic acid layer in mycobacteria = not possible to gram stain.
uses carbol-fushin, phenol and heat to penetrate the mycolic acid layerw
what is the function of the plasma membrane
selective permeability - uptake of nutrients and release of waste products
what are the constituents of the hydrophobic and hydrophilic parts of plasma membrane
hydrophilic = glycerol, phosphate, ethanolamine
hydrophobic = fatty acids
what does peptidoglycan consist of
amino acids and repeating units of carbohydrates
what is the function of pepidoglycan
mesh like layer that provides structural strength to cell envelope
acts like a sponge to collect soluble materials
contains plasma membrane, anchors surface molecules such as proteins and polymers
what does peptidoglycan backbone consist of
repeating disaccharides which form a polysaccharide backbone
NAM- n-acetylmuramic acid
NAG- n-acetylglucosamine
what is the stem peptide
amino acids attached to NAM
what gives the cell wall rigidity
crosslinking between adjacent polysaccharides
how might a bac cell wall resist osmotic pressure
glycosidic bonds in X and peptide bonds in Y planes provide high resistance
write a note on archaea pseudopeptidoglycan
performs similarly to peptidoglycan as it contains plasma membrane, provides rigidity + captures soluble materials
write a short note on peripheral membrane proteins
these are loosely attached, are typically lipoproteins (have a lipid tail [anchor])
define antiporter
transports molecules in opposite direction to H+ (to outside the cell)
define symporter
transports molecules in same direction as H+ (into the cell)
explain phosphotransferase system (PTS system)
is an example of group translocation and requires multiple enzymes. the transported substances are chemically altered (either phosphorylated or dephosphorylated)
write a note on the ABC transporter system
is a large family of transporters with wide target molecule range. requires 3 components:
1. substrate binding protein
2. transmembrane transporter
3. ATP hydrolysing enzyme in the cytoplasm
write a note on teichoic acids
simple polymers of repeating sugar units found on Gram+ cells. have high amounts of phosphate (neg charged)
2 main types:
- wall teichoic acid which is covalently linked to peptidoglycan
- lipoteichoic acids which are attached to plasma membrane
write a note on lipopolysaccharides
found on outer membrane of Gram neg cells. are neg charged. comprised:
- Lipid A = hydrophobic domain (endotoxin)
- core olgiosaccharide: hydrophilic non-variable core olgiosaccharide
- o antigen: repeating hydrophilic distal polysaccharide
what role has variability in the o antigen got for the bac cell
can dictate the host-range of organism and how well the bacteria can colonise
what is the S layer
protein layer on outer membrane or peptidoglycan.
what is a capsule
gelatinous polysaccharide layer outside the cell. they are hydrophilic and volume = 90% water. in infections they inhibit phagocytosis
what are fimbrae and pili
hair-like proteinaceous attachement that is expressed on the surface of the bacteria