week 1 -bacterial cell envelope

Question 1

Gram positive cell envelope

Answer 1

• Cryo-transmission electron micrograph
• PM plasma (cytoplasmic) membrane
• IWZ inner wall zone
  o Soluble low density components
• OWZ outer wall zone
  o Peptidoglycan network

Question 2

gram negative cell envelope

Answer 2

• Two membranes
• PG thin layer of peptidoglycan
• Outer membrane
  o An asymmetric lipid bilayer
  o The inner leaflet is composed mainly of phospholipid
  o Outermost layer is made of lipopolysaccharide or LPS
  o Relatively impermeable

Question 3

bacterial cytoplasmic membrane
primary roles:

Answer 3

• Separates the cytoplasm from the cell’s environment
• Permeability barrier
• Contains a range of diverse membrane proteins
  o Enzymes  (I.e. PBPs, peptidoglycan biosynthesis)
  o Transporters
• Energy conservation and consumption
  o Sit of the generation and use of the proton motive force

Question 4

bacterial cytoplasmic membrane:
phosphatidylethanolamine

Answer 4

primary lipid in bacterial CM

hydrophilic polar head
- phosphate and ethanolamine are charged

fatty acid chains form hydrophobic interior

Question 5

the bacterial cell wall

Answer 5

• Composed of peptidoglycan
• Forms a sac surrounding the cell
• Gives shape to bacteria
• Resists turgor pressure
  o In water environments
  o Without good peptidoglycan cell walls would absorb water till bursting
• Gram positive (thick) and Gram negative (thinner)

Question 6

structure of repeating unit of peptidoglycan

Answer 6

Repeating units of two sugars
- N-acetylglucosamine (G)
- N-acetylmuramic acid (M)

Joined by b 1,4 linkage

Tetrapeptide chain (side chain)
- Attached t0 NAM
- Contains D forms of amino acids
- Proteins made on ribosomes L
form)

Crosslinks
- Formed by transpeptidases
- Gram positive may have peptide inter bridge
- Crosslinks between peptide chains give strength

Question 7

cross linking in the Gram negative cell wall

Answer 7

Cross links between adjacent molecules
* Between amino acids
o Holds everything together
o Maintains rigidity
* Linkage always between 3rd and 4th amino acid

Question 8

Peptidoglycan – a target for antibacterial
Lysozyme

Answer 8

o First line of defence
o Found in tears, milk, saliva, mucous
o Cleaves the b(1-4) linkage in the peptidoglycan polysaccharide backbone

Question 9

Peptidoglycan – a target for antibacterial
penicillin

Answer 9

o Antibiotic
 Stops crosslinks from being made
 Bacteria bursts

Question 10

Penicillin targets transpeptidases

Answer 10

• Transpeptidases form peptide cross links between adjacent glycan chains
• Essential for structure of peptidoglycan
• Weakened cell wall with fewer cross links
  o Osmotic lysis
• Selective because peptidoglycan and transpeptidases are unique to bacteria

Question 11

Teichoic acids

Answer 11

• Up to 60% of the total mass of the cell wall
  o Polymers of sugars or sugar derivatives such as glycerol and ribitol
  o Negatively charged
• Wall teichoic acids
  o Covalently linked to the peptidoglycan

Question 12

Lipoteichoic acids

Answer 12

o Anchored in the cytoplasmic membrane via glycolipids
- Function
o Protecting the Gram positive envelope
o Important in bacteria-host interactions
 Adherence and colonisation of host cells surfaces
o Often recognised by host immune system

Question 13

overall net charge of any bacteria is:

Answer 13

negative

Question 14

GRAM NEGATIVE CELL WALL
lipopolysaccharide

Answer 14

part lipid part sugar

Question 15

GRAM NEGATIVE CELL WALL
O-specific polysaccharide

Answer 15

• Highly variable
• Antigenic
• Made up of repeated units
• 3 sugars and a branch

Question 16

GRAM NEGATIVE CELL WALL
core polysaccharide

Answer 16

• Highly conserved (especially the inner core)  likely to be the same/very similar across gram negative bacteria
• Contains KDO and other unusual sugars

Question 17

GRAM NEGATIVE CELL WALL
Lipid A

Answer 17

• Variation in the length and degree of subsitiution of the acyl chains

Question 18

Gram negative periplasm

Answer 18

• Subcellular compartment between the cytoplasmic and outer membranes
  o Compartment between the two membranes
• 10-20% of the volume of the cell
• High protein content
  o Proteins for: cell wall synthesis and uptake and transport of nutrients
• Oxidising environment – formation of disulphide bonds in proteins
  o To give rigidity
  o Have to be formed outside cell
• Contains chaperones that ensure the correct folding of other proteins

Question 19

do gram positives had a periplasmic space

Answer 19

• IWZ inner zone wall
  o Soluble low density components
  o May be a periplasmic space
  o Could be site of enzyme reactions

Question 20

proteins in the outer membrane

Answer 20

• For transport
  o Nutrients in
  o Waste out
• Porins
• Span outer membrane
• Beta barrel
• Solutes diffuse through the water filled channel
• Many antibiotics diffuse though porins

Question 21

the surface layer OR s layer

Answer 21

• Regularly spaced array of protein subunits
• Self assemble into a structure which coats the entire cell creating a porous lattice
• Covalently attached to the peptidoglycan in Gram positives and to the O-polysaccharide chains of LPS in Gram negatives
  Made of protein units shaped so they fit together (self assemble)
  Not a membrane it is protective
• Porous lattice

Question 22

capsules and slime

Answer 22

• Extracellular polymeric substances (EPS)
• Often polysaccharides (like O side chains of LPS)
• Capsule
  o Discrete layer
  o Covalentlu attached to OM lipids or PG
• Slime
  o Not covalently attached

In conjunction or an alternative to the S-layer
Capsule is attached
Slime is not attached