Bacterial Cell Walls

Question 1

Primary function of the cell wall

Answer 1

-prevent cells from bursting due to osmotic pressure
-provide cell shape and rigidity

Question 2

gram positive bacteria

Answer 2

-thick cell wall and no outer membrane

Question 3

gram negative bacteria

Answer 3

-thin cell wall
-have an outer membrane

Question 4

peptidoglycan

Answer 4

-archaea and eukarya lack peptidoglycan
-peptidoglycan is a lattice like structure formed from chains of glycans linked together by peptide bridges

Question 5

sugar backbone of peptidoglycan

Answer 5

-alternating N-acetylglucosamine (NAG) and N actylmuramic acid (NAM)

Question 6

peptide crosslinks of peptidoglycan

Answer 6

-short peptide chain covalently linked to the peptide from an adjacent chain via peptide bond

Question 7

glycan chains of peptidoglycan

Answer 7

-n acetylglucoasmine (GlcNAC, NAG) and N-acetylmuramic acid (MurNAc, NAM), linked by beta 1-4 linkages (glycosidic bond)

Question 8

peptides of peptidoglycan

Answer 8

-sequence varies between species conserved within a single organism
-D isomers of AA (L isomers are proteins)
-peptide bonds sit between position 3 (DAP) and position 4 (D-alanine)

Question 9

general description of gram negative bacteria cell wall

Answer 9

-typically 1-3 peptidoglycan layers about 2-7nm
-flexible, porous but still quite strong
-additional strength from outer membrane

Question 10

general desription of gram positive bacteria

Answer 10

-15+ layers of peptidoglycan
-interbdiges help connect peptidoglycan layers, these are also peptide crosslinks extended by a few AA acids and sequences vary

Question 11

peptidoglycan peptide sequence

Answer 11

-sequence of peptide in peptidoglican is conserved for a given bacterium
-not a random peptide - machinery assembles this seqeunce
-different bacteria have evolved slightly different machinery
-result is that you get different sequences in different organisms

Question 12

Teichoic acids

Answer 12

-Gram Positive
-long polymers of glycerol phosphate or ribitol phosphate with a D glucose and or a D alanine
-covalently attached to peptidoglycan or cytoplasmic membranes
-strength through ionic interactions with neighboring strains bridges by metal ions
-help trap divalent metal ions
-barrier an attachment functions

Question 13

what is a teichoic acid connected to peptidoglycan called

Answer 13

-teichoic acids or wall techoic acids

Question 14

what is a teichoic acid connected to cytoplasmic membrane called

Answer 14

-lipotechoic acids

Question 15

wall associated proteins

Answer 15

-gram positive
-cell adhesion
-typically associate covalently or non covalently with the cell wall
-some interact with teichoic acid

Question 16

cell wall being porous and dynamic

Answer 16

-cell wall not generally a permeability barrier except to large molecules like large proteins or protein complexes
-cell walls are not stagnant they are constantly being synthesized degraded and remodeled under many conditions (especially through cell division)

Question 17

gram staining basics

Answer 17

-cells are stained uniformly with insoluble crystal violet idoine complex
-cells are decoloruized with alcohol
-cells are counter stained with safranin

Question 18

gram positive gram stain

Answer 18

-thick layer of peptidoglycan is dehydrated pores close and prevent escape of CV
-cells are stained purple (dark dominant over pink counterstain)

Question 19

gram negative gram stain

Answer 19

-decolourizing agent degrades outer membrane, thin porous peptidglycan layer does not retain pruple stain
-cells appear pink due to safranin

Question 20

bacteria that lack cell walls

Answer 20

-mycoplama pneumonia
-intracellular parasite that lives within host cell
-minimal osmotic pressure within host cell
-cell burst in low solute environments
-specialized and unually strong cell membrane
-does not have cell wall or outer membrane