Gram Positive Walls

Question 1

What is Murien?

Answer 1

Peptidoglycan

Question 2

What are the two alternating sugars that make up the PG backbone? how are they connected?

Answer 2

Beta 1,4 links connection

NAG and NAM connected by short peptides

Question 3

What two amino acids alternate while connected to NAM. What amino acid is always in the 3rd position?

Answer 3

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

Question 4

Explain the difference between L and D amino acids

Answer 4

L amino acids are isomers found in proteins

D amino acids are only ever found in PG

Question 5

How is peptidoglycan directly cross-linked?

Answer 5

Direct linkage: A carboxyl group of alanine linked to the amino group of DAP or lysine

Question 6

How is peptidoglycan indirectly cross-linked?

Answer 6

Indirect linkage: pentaglycine bridge

Question 7

Explain the cross linkage in gram negative walls

Answer 7

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

Question 8

Explain the cross linkage in gram positive walls

Answer 8

This uses many pentaglycine bridges between the alanine and DAP groups which creates extensive cross links.

Question 9

true or false, only NAM have amino acid side chains not NAG

Answer 9

true

Question 10

t or f, brauns lipo protein in gram negative bacteria is linked to DAP

Answer 10

True

Question 11

what is transpeptidation?

Answer 11

the linkages between NAM groups of the peptidoglycan layer

Question 12

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?

Answer 12

Penicillin

Question 13

True or false, penicillin breaks the transpeptidation bonds in peptidoglycan layer

Answer 13

False, it only prevents them from forming. If they have already formed penicillin has no affect

Question 14

what will be the effect of penicillin on PG layer for cells who are in the stationary phase

Answer 14

These cells are not growing and therefore there are no new peptide bonds being formed. Therefore it has no effect on non growing cells

Question 15

Explain how penicillin works as an antibiotic (3 points)

Answer 15

• It prevents cross linkage in PG
• this makes the cell osmotically fragile
• cells will lyse more readily

Question 16

What is the following statement explaining. 50% peptidoglycan, up to 50% teichoic acids, and no lipids

Answer 16

Gram positive walls

also no OMP’s but that is obvious

Question 17

Explain what teichoic acids are

Answer 17

• Polymers of glycerol or ribitol connected by phosphate bonds
• Amino acids and sugars are often attached to them
• exposed on surface

Question 18

What are Wall teichoic acids linked too?

Answer 18

Only NAM (muric acid) never glucoseamine (NAG)
linked to 6OH group of NAM

Question 19

What are lipo teichoic acids linked too?

Answer 19

the cytoplasms glycolipids

Question 20

Can ribitol based Teichoic acids be lipo teichoic acids?

Answer 20

No, only glycerol since they connect to glycolipids of the cytoplasm

Question 21

Explain the functions of teichoic acids (4)

Answer 21

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

Question 22

Explain Archaea cell walls. what is the most common one? (4)

Answer 22

• 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

Question 23

what is the main difference between PG and Pseudomurein?

Answer 23

• 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