2-3: Bacterial Cell Walls

Question 1

What is the function of the cell wall

Answer 1

Prevent cell from bursting due to osmotic pressures (due to higher concentration of solutes in cell), cell shape, rigidity

Question 2

What is the cell wall like in gram-negative bacteria

Answer 2

Thin cell wall, contain an outer membrane

Question 3

What is the cell wall like in Gram-positive bacteria

Answer 3

thick cell wall with no outer membrane

Question 4

Do all bacteria contain a cell wall?

Answer 4

For the most part, yes (some RARE cases don’t)

Question 5

What is the cell wall comprised of

Answer 5

Peptidoglycan

Question 6

Structure of peptidoglycan

Answer 6

Lattice like structure formed of chains of glycans linked by peptide bridges

Question 7

What is the peptidoglycan sugar backbone made of

Answer 7

N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM)
alternating

Question 8

How are the peptide crosslinks attached in peptidoglycan?

Answer 8

Short, covalently linked peptide chains that are attached to NAM

Question 9

What kind of linkage connected NAM and NAG

Answer 9

B(1-4) linkages (glycosidic bonds)

Question 10

What kind of isomer makes up peptides

Answer 10

D-isomer of aa

Question 11

Peptide bonds form between what positions

Answer 11

Position three (DAP/Lys) and position four (D-alanine)

Question 12

How does the sequence of peptides vary?

Answer 12

It varies between species, same in the same species

Question 13

How many peptidoglycan layers do gram negative bacteria have

Answer 13

~1-3 (2-7nm thick)

Question 14

Describe the structure of the cell wall in gram-negative bacteria

Answer 14

Flexible, porous, strong. Needs additional outer membrane to provide extra strength

Question 15

How many peptidoglycan layers do gram positive bacteria have

Answer 15

15+ (20-35nm thick)

Question 16

What are Interbridges?

Answer 16

Peptide crosslinks present ONLY in gram positive cells to help connect different peptidoglycan layers

Question 17

What are teichoic acids?

Answer 17

Long polymers of glycerol phosphate or ribitol phosphate with an attached D-glucose or D-alanine

Question 18

What are teichoic acids attached to?

Answer 18

Peptidoglycan (teichoic acids). CM (lipoteichoic acids)

Question 19

What is the role of teichoic acids

Answer 19

Provide cell strength (ionic interactions between neighoring metal ions), trap divalent metal ions, barrier and attachment

Question 20

What is the function of wall-associated proteins?

Answer 20

Cell adhesion

Question 21

Are wall associated proteins associated in gram + or - bacteria? How do they associate?

Answer 21

Positive. They associate covalently or non covalently with the cell wall or teichoic acid

Question 22

How are cell walls dynamic?

Answer 22

Not stagnant. Constantly being synthesized, degraded, remodeled

Question 23

Describe the permeability of the cell wall

Answer 23

Very porous. Generally not a permeability barrier to anything except large molecuels (proteins)

Question 24

What colour do gram-positive bacteria stain and why

Answer 24

Purple
Peptidoglycan is dehydrated and pores close trapping crystal violet

Question 25

What colour do Gram negative bacteria stain and why?

Answer 25

Decolourizing agent (alcohol) degrades the outer membrane, the porous peptidoglycan layer does not retain purple stain. Thus pink due to safranin counterstain

Question 26

What is the bacteria that lacks a cell wall?

Answer 26

Mycoplasma pneumoniae

Question 27

How does Mycoplasma pneumoniae compensate for not having a cell wall?

Answer 27

Contains an unusually strong cell membrane. It is an intracellular parasite that lives within host cells - thus minimizing the osmotic pressure