Bacterial Cell Envelope

Question 1

what are the 3 major components of most bacterial envelopes

Answer 1

plasma membrane, peptidoglycan and envelope proteins

Question 2

what are the key differences between gram pos and neg

Answer 2

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

Question 3

what are the features of a mycobacterial envelope

Answer 3

thin peptidoglycan layer, single membrane, mycolic acid layer (hydrophobic). has arabinogalactan which links peptidolgycan and mycolic acids

Question 4

what are the features of a wall-less bac envelope

Answer 4

no peptidoglycan and must live in osmotically balanced environment

Question 5

what are the chemicals used in gram stain

Answer 5

crystal violet, iodine, ethyl alcohol, safranin

Question 6

how does the ziehl nielsen stain work

Answer 6

mycolic acid layer in mycobacteria = not possible to gram stain.

uses carbol-fushin, phenol and heat to penetrate the mycolic acid layerw

Question 7

what is the function of the plasma membrane

Answer 7

selective permeability - uptake of nutrients and release of waste products

Question 8

what are the constituents of the hydrophobic and hydrophilic parts of plasma membrane

Answer 8

hydrophilic = glycerol, phosphate, ethanolamine

hydrophobic = fatty acids

Question 9

what does peptidoglycan consist of

Answer 9

amino acids and repeating units of carbohydrates

Question 10

what is the function of pepidoglycan

Answer 10

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

Question 11

what does peptidoglycan backbone consist of

Answer 11

repeating disaccharides which form a polysaccharide backbone

NAM- n-acetylmuramic acid
NAG- n-acetylglucosamine

Question 12

what is the stem peptide

Answer 12

amino acids attached to NAM

Question 13

what gives the cell wall rigidity

Answer 13

crosslinking between adjacent polysaccharides

Question 14

how might a bac cell wall resist osmotic pressure

Answer 14

glycosidic bonds in X and peptide bonds in Y planes provide high resistance

Question 15

write a note on archaea pseudopeptidoglycan

Answer 15

performs similarly to peptidoglycan as it contains plasma membrane, provides rigidity + captures soluble materials

Question 16

write a short note on peripheral membrane proteins

Answer 16

these are loosely attached, are typically lipoproteins (have a lipid tail [anchor])

Question 17

define antiporter

Answer 17

transports molecules in opposite direction to H+ (to outside the cell)

Question 18

define symporter

Answer 18

transports molecules in same direction as H+ (into the cell)

Question 19

explain phosphotransferase system (PTS system)

Answer 19

is an example of group translocation and requires multiple enzymes. the transported substances are chemically altered (either phosphorylated or dephosphorylated)

Question 20

write a note on the ABC transporter system

Answer 20

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

Question 21

write a note on teichoic acids

Answer 21

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

Question 22

write a note on lipopolysaccharides

Answer 22

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

Question 23

what role has variability in the o antigen got for the bac cell

Answer 23

can dictate the host-range of organism and how well the bacteria can colonise

Question 24

what is the S layer

Answer 24

protein layer on outer membrane or peptidoglycan.

Question 25

what is a capsule

Answer 25

gelatinous polysaccharide layer outside the cell. they are hydrophilic and volume = 90% water. in infections they inhibit phagocytosis

Question 26

what are fimbrae and pili

Answer 26

hair-like proteinaceous attachement that is expressed on the surface of the bacteria