Peptidoglycan and cell wall

Question 1

PG structure

Answer 1

Polymer of identical subunits of peptidoglycan

Question 2

Glycan portion

Answer 2

2 sugar derivatives:
- N-acetylglucosamine (NAG)
- n_acetylmuramic acid (NAM)

Question 3

Peptide portion of PG

Answer 3

peptide chain of 4 AAs
-attached to NAM
-Alternating L- and D-amino acids
-Several different AAs including:
- D-Glutamic acid
- D-Alanine
- meso-Diaminopimelic acid (DAP)

Question 4

Gram positive PG aa

Answer 4

Most have L-lysine instead of DAP

Question 5

How are PG subunits linked

Answer 5

Peptide bridge cross links
-for adjacent chains, Not NAG and NAM subunits

Question 6

stats on gram positive PG

Answer 6

• 15-50% of dry weight of cell wall
• Tertrapeptide cross-linkage (high percentage of 90-93%)
  -Cross-linkage proportional to rigidity
  -makes membrane very strong
  -thick PG layer

Question 7

Gram negative PG

Answer 7

-Meso-Diaminopimelic acid
-No interbridge (direct covalent linkage between peptides)
- 5-10% of dry weight of cell wall
-low % of terapeptide cross-linkage
-Thin PG layer
-PG provides less protection and the teichoic acids are secondary polymers that gives the structure rigidity and negative charge)

Question 8

PG function

Answer 8

Rigid, multilayer sheet
-Primary protective function
-Primarily in Gram +
-Protects also against osmotic pressure but is porous enough to allow nutrients in

Question 9

why is osmotic pressure a problem

Answer 9

Most microbial environments are hypotonic with little solute which would cause the cell to lyse
-Hypertonic would strip water from PG

Question 10

Post-penicilin incubation

Answer 10

Penicillin used to get rid of PG
-Used to prove NB of PG:
* In isotonic solution they are fine without it
*If placed in hypertonic solution, it will burst

Question 11

Lysozyme effect on PG

Answer 11

Breaks down NAG and NAM bond

Question 12

Penicilin effect on PG

Answer 12

Prevents NAG and NAM linkage from being FORMED