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BIOC17 lec 7 notes.docx

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University of Toronto Scarborough
Biological Sciences
M Terebiznic

Lecture 7: Bacterial Cell Wall – Structure, Synthesis and Pathogenesis Skipped class – recording starts at slide 9 Figure 21.1 - Reason for creating taxony – gram -/+  a lot of properties similar between these structures - When doing phylogeny – not enough that gram +/-  found + in one photogenic grp - All the rest is gram -  completely different taxa – spread all over the domain bacteria and prokaryotes - How we now see gram +/- Gram negative cell walls - Thin proteoglycan layer - Replasmic space - Outer membrane – liopolysaccarides facing exterior - Phospholipids - Other protein in the outermembrane and glycoprotein layer  connect with outer membrane - Larger complex periplasmic space – 20-40% of body -- huge component of cell body - Many enzymes that will process molecules necessary for nutrition of bacteria – from here they pass and put into cytoplasm for metabolism o take care of antimicrobial components here  these try to destroy the bacteria Gram positive cell wall - Thick petidoglycan layer – connected to plasma membrain by liptechoic acids - Lipotechoic acid = alchol polymer – inserted into plasma membrain - Teichoic acid - Space is much smaller – important with many functions but not as complex - Structure is very strong because its very strong - Can break down bacteria and still retrieve the cell wall like a sock Techoic acid - Molecule specific to gram + cell wall - Glycerol = bound to phosphate form polymer - Alcoholic version of sugar ribose – ribitol - Connect petidoglycan with plasma membrane - Protrude – exposed on top of glycan layer – negative charge property to cell wall - Important for humans b/c its how our immune system identifies it o Without this difference we would be dead o Our immune systems exploit the difference and our technology, antibiotics work based on these differences Peptidoglycan Structure - Like fabric - Have sugar pattern that repeats - N-actyl –forms beads - Peptides between strands bind each other - Keep layering on top of each other  more layers thicker and stronger - Next slide: - Sugars bound by beta(1-4) bounds – seen in other structures – cellulose, glycogen, shrimps (exoskeleton, cell walls) - Very difficult to break - Different amino acids – all of them in L configuration in humans o D configuration is the other side of the mirror o Important because not recognized amino acids in the D configuration – can’t kill the cell this way o Meso-diamino-pimelic acid – specific to bacteria – the immune response can recognize the difference o Very simple, but important difference between us and them Cross-linking and inter-bridge peptide - Bridge between the peptides – alaine and DAP – cross link strains - Gram + it is another peptide  lysine – crosses the strands - Can differentiate +/_ this way - Gram + will have different interbridge peptides - *don’t need to know the possibility, just know that the bridge composition can be different - extra amino residue that can interact Peptidoglycan Synthesis - made in cytoplasm – cell has to mount this large structure outside - has to be assembled outside cell - molecules are charged and hterfore don’t cross the plasma membrane well - involves helpers – UDP = like ATP or ADP but with a uricine - mobilize sugars - bactoprenol = the one that allows all the components to flip across plasma membrane from cytoplasm into outer membrane space - use glucose - next slide: - has phospates that binds N-acetylmuramic acid - which will be incerted in plasma membrane – the portion that has no charge (phosphates)  phosphates bound to sugar Animation diagram - UDP-NAM-  loaded with sugar – binds pentapepide - In cytoplasm – binds to bactoprenol and donate phophate NAM and peptide  lipid 1 - UDP-NAG – donate sugar and pentapeptide  lipid 2 - Now it flips to periplasm – exposed NAM-NAG to periplasmic space - Petidoglycan - Bactoprenol lost the phosphate  goes back to cytoplasm – ready to be reloaded again Cell Wall Formation - cell to growth – for body to increase in size need to add more petidoglycan - Open part in petidoglycan mesh polymer has to be created - Enzymatic complex – autolysins – that creates this - incertion has to be accurate, fast o Break in the fabric and cause lysis and cell to break o As much as cell wall is growing you see more breaks in the wall  as much breaks as possible to increase volume – if you block the protein that makes the breaks the cell will die Tetrapeptide Cross-links - Then you need to bridge the peptiodglycan – start as pentapeptide  end as heptapeptide - Enzymatic reaction by transpeptidases  binds the 2 amino acids - Gram - and + have the different amino acids Osmotic Protection - Primary function of cell wall – if not there it would swell til it burs
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