The Cell Wall Flashcards
What are the five main functions/uses of the bacterial cell wall
protect against osmotic pressure (lysis)
determine cell shape
protect against toxic substances
contribute to pathogenicity
contain the active site for several antibiotics
what are three antibiotics that utilize cell wall active sites?
penicillin, cephalosporins, vancomycin
What is the cell wall in bacteria composed of?
peptidoglycan (murein)
What is the basic structure of the bacterial cell wall?
peptid crosslinks (4 amino acids) sandwiched in between two glycan chains
what are the two sugars in the glycan chain?
N-acetylglucosamine (NAG), and N-acetylmuramic acid (NAM)
What kind of linkage is between the two sugars in the glycan chain?
Beta 1,4 - glycosidic linkages
What is the phylum of gram + bacteria?
Firmicutes
What is the structure of the gram + bacterial cell wall?
NAM , L-alanine , D-hydroxylated glutamic acid , L-lysine , D - alanine
What is the phylum of gram - bacteria?
Proteobacteria
what is the structure of a gram - bacterial cell wall?
NAM, L-alanine, D-glutamic acid, diaminopimolic acid (DAP), D-alanine
Why are L and D linkages important in the bacterial cell wall?
they make it more difficult to break down by proteases
In Gram + bacteria, what links the L-lysine and D-alanine?
A crosslink bridge composed of 5 amino acids?
In Gram - bacteria, what links the diaminopimelic acid and D-alanine?
a direct crosslink with no amino acids
What are the major differences between Gram + and Gram - bacteria?
Gram + bacteria have no outer membrane, a large thick cell wall with 4-25 sheets, and contain teichoic acids.
Gram - bacteria have an outer membrane, and a thin cell wall with 1-3 sheets
Why is a cell wall necessary in prokaryotes?
due to the lack of membrane bound organelles, there is a large amount of dissolved solute right in the cytoplasm, this leads to a high osmotic pressure with the tendency of water to come into the cell. the cell wall prevents this.
What antibiotics have an active site in the cell wall?
penicillin, cephalosporins, vancomycins
what is murein?
peptidoglycan
What is the glycan chain composed of in bacteria?
N-acetylglucosamine, N-acetylmuramic acid. Linked by a B 1,4, glycosidic linkage
T/F, peptides will always come off of N-acetylmuramic acid
T
What part of our innate immune system can break up the B 1,4 linkages in the peptide chains?
lysozyme
What are 3 features of Gram + bacteria?
no outer membrane
thick cell wall
contains teichoic acids
What are 2 features of Gram - bacteria
outer membrane
thin cell wall
What is teichoic acid?
chains of phosphodiester linked glycerol or ribitol
How do glycerol and ribitol allow for modification of teichoic acids?
can find D-alanine or glucose attached to the glycerol or ribitol
What is a lipoteichoic acid?
a teichoic acid that is embedded in the cell membrane
What is lipopolysaccharide?
a 3 component molecule that takes up most of the outer leaflet of the outer membrane
What is the inner leaflet of the outer membrane composed of?
Brauns lipoprotein, connects to cell wall
What are the 4 steps of gram staining?
- crystal violet (primary stain) both cell walls affix the dye
- grams iodine (fixative) both cell walls still purple
- Alcohol (decolorizer) Gram - now colorless
- Safranin (red dye) stains Gram - pink
What stain is used to identify mycobacterium?
acid-fast stain
What is arabinogalactan?
a long polysaccharide made up of arabinose and galactose
T/F, mycobacterium have no peptidoglycan
F, have a very thin layer with a higher degree of crosslinking
What are the two components of the mycomembrane?
inner leaflet and outer leaflet
What is the inner leaflet of the outer membrane composed of in mycobacterium?
mycolic acid
what is mycolic acid?
a long hydrocarbon with 2 tails.
How long are the two hydrocarbon tails in mycolic acid
one is 20 Carbons long, the other is 60-90 carbons long
Why do mycobacterium grow slowly?
the combination to the dense sugar network and the hydrophobic mycomembrane covering the peptidoglycan makes getting nutrients in difficult
T/F mycoplasma is the most common contaminant of tissue culture cells
true
Give 3 structural features of mycoplasma
no cell wall
sterols found in membrane for structural integrity
extremely tiny 0.1-0.5 micrometers
What is the cell wall in archaea made up of?
pseudopeptidoglycan
What two sugars make up pseudopeptidoglycan in archaea and what links them
N-acetylglucosamine and N-acetyltalosaminuronic acid, linked by a B 1,3 glycosidic linkage
what are the peptide crosslinks made up of in archael cell walls?
varying amino acids used, all in the L conformation
How come archaea have all L sugars, even though proteases can then break them down
archaea are extremophiles, they primarily don’t interact with hosts and therefore do not need to be immune to proteases
What are S layers?
consist of interlocking proteins or glycoproteins that form a paracrystalline structure
what are 3 features of S layers?
form a sheath around the cell
common to see in archaea, paracrystalline structure with symmetry that can be hexagonal, tetragonal, trimeric
