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MMG Cell Walls and Membranes


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What wall is specialized only to bacteria?
-a bacterial cell wall composed of peptidoglycan
-backbone of polymerized sugars and peptide cross-links
Typically, what is the turgor pressure found in bacterial cells?
-high, around 2 atm so cell wall protects it from osmotic forces
How do antibiotics correlate to cell walls?
-they attack it which is why eukaryotes can take these (no cell walls, just membranes)
What do peptide cross-links do?
-hold together the strands of glycan and form the rigid structure of the peptidoglycan
*cross-links vary between bacterial species
How do you make a peptidoglycan?
-insert N-acetlyglucosamine/N-acetylmuric acid/pentapeptide precursor into the growing part of the wall
-a precursor must be linked to a hydrophobic lipid carrier to cross the cytoplasmic membrane
What is the hydrophobic lipid carrier that is able to cross the cytoplasmic membrane of bacteria (during formation of a peptidoglycan)?
What is the final step in the synthesis of petidoglycan?
-Transpeptidation which includes the formation of prptide cross-links
How does penicillin affect bacteria?
-it inhibits the transpeptidation step of peptidoglycan synthesis (all penicillin derivatives work this way as well)
How is cell shape generated?
-cell wall material is put in different locations which deides what the cell will look like
Where is the cell wall inserted to form a bacilli?
-cell wall material inserted throughout cell cylinder
How are streptococci formed?
-insertion of cell wall material at the site of cell division
How are corynebacterium formed?
-insertion of cell wall material at the site of cell division and at the cell poles
What creates high turgor pressure in cells?
-most bacteria are in low solute environments, whereas they have high solute in their cells (more water comes in)
*without cell wall, membrane would lyse from continued osmosis
How do halophilic archaea live in such high salt conditions?
-pseudopeptidoglycan layers
-different plasma membrane composition
-make compatible solutes to increase internal solute concentrations
What are some of the compatible solutes made by halophilic archaea to increase internal solute concentrations?
-K+ ions
-amino acids
What is the percent composition difference in gram + and - bacteria?
-90% to 10%
Which gram bacteria is more sensitive to penicillin and why?
-Gram + because they have more peptide cross-links and interbridges (because they have so much peptidoglycan)
Which acids in Gram+ cells have negative charges?
-Teichoic acid
-Lipoteichoic acid
*What stain would you use to highligh a Gram+ cell?
What are the cell walls of Mycobacterium like?
-similar to Gram+ bacteria
-Mycolic acid residues are linked to the peptidoglycan
What are mycolic acids?
-long chain fatty acids (extremely hydrophobic)
-make up 60% of total cell wall mass)
-responsible for the "acid fast" properties of Mycobacteria
*free lipids, glycolipids, and peptidoglycolipids are also mycolic acids
What part of a Gram- cell has the endotoxin?
What does this cause?
-In the LPS layer (made up of polysaccharide and Lipid A)
-can cause fever and shock in patients
Where is lysozyme found (not lysosomes)?
-in saliva
What does LPS stand for?
Gram- cell walls have multiple phospholipid layers. How similar are they?
-Not similar: each layer is different from the other
What is porin?
-means pores that allow charged products to pass through
Which gram bacteria has peptidoglycan?
How about interbridge?
What is this interbridge made of?
-both bacteria do (Gram+ has much more!)
-Gram+ has interbridge
-interbridge made of pentaglycine
In terms of location, what does an O antigen mean?
How about H7?
-O= outside sugars/a cell wall antigen
-H= flagella antigen
-K= capsular antigen
Describe E coli O157:H7
-cell wall antigen #157, flagella antigen #7
-causes foodborne illness (like spinach!)
Describe E coli K1.
-refers to capsular antigen #1
-encapsulated strain of E. coli
-causes neonatal sepsis
What 2 simple eukaryotic groups aren't affected by penicillin even though they HAVE cell walls?
-fungi and algae
What does a fungi cell wall consist of?
-80-90% polysaccharides
-glycoproteins (glucans and mannans)
What is chitin?
-found in fungal and algal cell walls
-polymer of N-acetylglucosamine
What do all algal cell walls consist of?
-presominantly polysaccharides (similar to plants but diverse constituents)
What are two special components that belong to two different algaes?
-calcium carbonate in coralline algae
-silica (sand) in diatoms
What two common membranes in eukaryotic (one is also in bacteria) cells are made of phospholipid bilayers?
What are in this layer?
-Plasma membranes for both
-Organellar membranes for eukaryotes
-both embedded with proteins
What causes these membranes to form and make them good barriers?
-amphipathis nature
How does the amphipathic nature of phospholipids lead to the bilayer?
-fatty acids interact through hydrophobic interactions
-phosphate groups interact with the aqueous environment through h-bonds
What are some other structures found in/around a cell membrane?
-integral proteins
-integral glycoproteins
-peripheral proteins
*CHO's on these (look like little bird feet)
What are sterols?
-found in eukaryotic membranes
-rigid, planar molecules that provide rigidity to membranes
What is different with Archaea membranes?
-chemically unique: 'ether' linkages connect glycerol to isoprene NOT fatty acids
-can still form bilayers as well as monolayers which are very resistant to disruption
How do membranes help photosynthetic prokaryotes?
-by harvesting light energy
Overall, what are some functions of a membrane?
-selective permeability
-energy production
-anchor proteins needed for transport, bioenergetics
What do transport proteins do?
-bring solutes into cells against a concentration gradient (concentration usually higher in the cell)
How is voltage created in a cell?
-by creating an electrical gradient
-this is done by the import and export of charged ions (EX: H+ protons)

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