Gram Positive Walls Flashcards
What is Murien?
Peptidoglycan
What are the two alternating sugars that make up the PG backbone? how are they connected?
Beta 1,4 links connection
NAG and NAM connected by short peptides
What two amino acids alternate while connected to NAM. What amino acid is always in the 3rd position?
L and D amino acids alternate while connected to NAM
originally there is 5 by an Alanine is lost in formation of cross links
Lysine or DAP are ALWAYS IN 3RD POSITION
Explain the difference between L and D amino acids
L amino acids are isomers found in proteins
D amino acids are only ever found in PG
How is peptidoglycan directly cross-linked?
Direct linkage: A carboxyl group of alanine linked to the amino group of DAP or lysine
How is peptidoglycan indirectly cross-linked?
Indirect linkage: pentaglycine bridge
Explain the cross linkage in gram negative walls
Typically is a simple connection between the alanine group of one NAM to the DAP group of the next NAM. IT is a simple connection
Explain the cross linkage in gram positive walls
This uses many pentaglycine bridges between the alanine and DAP groups which creates extensive cross links.
true or false, only NAM have amino acid side chains not NAG
true
t or f, brauns lipo protein in gram negative bacteria is linked to DAP
True
what is transpeptidation?
the linkages between NAM groups of the peptidoglycan layer
the cross linkage between the carboxyl group of alanine f one NAM and the amino group of DAP on the next NAM can be prohibited by what molecule?
Penicillin
True or false, penicillin breaks the transpeptidation bonds in peptidoglycan layer
False, it only prevents them from forming. If they have already formed penicillin has no affect
what will be the effect of penicillin on PG layer for cells who are in the stationary phase
These cells are not growing and therefore there are no new peptide bonds being formed. Therefore it has no effect on non growing cells
Explain how penicillin works as an antibiotic (3 points)
- It prevents cross linkage in PG
- this makes the cell osmotically fragile
- cells will lyse more readily
What is the following statement explaining. 50% peptidoglycan, up to 50% teichoic acids, and no lipids
Gram positive walls
also no OMP’s but that is obvious
Explain what teichoic acids are
- Polymers of glycerol or ribitol connected by phosphate bonds
- Amino acids and sugars are often attached to them
- exposed on surface
What are Wall teichoic acids linked too?
Only NAM (muric acid) never glucoseamine (NAG) linked to 6OH group of NAM
What are lipo teichoic acids linked too?
the cytoplasms glycolipids
Can ribitol based Teichoic acids be lipo teichoic acids?
No, only glycerol since they connect to glycolipids of the cytoplasm
Explain the functions of teichoic acids (4)
1) many phosphate groups (between glycerol and ribitol units) make it very negative: controls cation supply
2) gram positive pathogens use it to bind host cells
3) anchors the PG to the PM (lipo teichoic acids)
4) aid in cell division
Explain Archaea cell walls. what is the most common one? (4)
- they are more diverse than bacteria walls
- they DONT HAVE peptidoglycan
- most common is a PM and an S layer
- some have a homogenous Pseudomurein layer
what is the main difference between PG and Pseudomurein?
- Pseudomurein only has L amino acids, (PG has D too)
- NAM is replaced with a different sugar
- beta 1,3 connection instead of PG’s 1,4
- lysine connects them instead of DAP
