Module 9 Flashcards
Cell envelope of gram positive and negative
gram negative -(cytoplasmic membrane, peptidoglycan layer, outermembrane)- thin PG layer
gram positive- (cytoplasmic membrane and PG)- thick PG layer
cell wall = PG + outermembrane or just the PG and sme include the capsule
periplasm is the space btw cm and pg or pg and outermembrane
what diffuses through the cytoplasmic membrane freely
hydrophobic substances and water
hydropjhillic do not - proteins and ions
What enviroment does the bacteria live in
hypotonic enviroments cause cell to swell and osmotic lysis
cytoplasmic membrane protein functions
transport- import and export
signal transduction
energy transduction-ETC and the PMF
mycoplasmas bacteria
have no cell wall- pleomorphic
- parasitic
- isotonic since our and their cell are both hypotonic
- incorperate sterols into membrane
how do bacteria survive a hypotonic conditions
have cell wall like the outermembrane and PG pushes agaianst the expanding cytoplamic membrane
what do gram positive and neg bacteria become when PG degragation in an isotonic enviroment
when they are in isotonic enviroment the gram negative become spheroplasts and gram positive become protoplasts
why is PG a good antibiotic target
what antibiotics target the PG
surface layer
in bacteria but not us humans
- vancomycine and Blactams
Peptidgylcan strructure
NAM-NAG surgar is the glycan backbone and NAM connects the undrpcyl and the penta peptide
glycan strands are attached through crosslinks between the 3-4 peptide and the meso-diaaminopimelic / l-lysine(3) and the (4) is when the terminal D-ala leaves
gram neg- has has direct link an amide bond (meso-dap for position 3)
gram pos- have peptide link (interpeptide bridge ) (l-lyssine for position 3)
Synthesis of Lipid 2
- UDP and nag change to udp and NAM
- NAM starts growigng the peptide chain
- Name with pentapeptide phosphoratlate to the undercapriynl (filpapse )
- lipid 1 = undercaprynl and nam + pentapeptide
- NAG is attache making lipid 2 = nam and nag and penta peptide
- flappase flips the lipid 2 from the cytoplasm to the periplasm
Whar is lipid 2
it is a PG precursor made of NAM-NAG disaccaride and pentapeptide bound to membrane by undecaprenol
How to convert L-Ala from humans to D-Ala
L-Ala is convereted to D ala by alanine racemase and then D-ala-D-ala is done by D-ala-D-ala ligase
L-ala to D-ala enxyme
alanine racemase
Cycloserine
inhibits alanine racemase and D-ala-d-ala ligase
Penicillin binding protein components
glycotransferase domain connects the NAM and NAg of the peptidoglycan chain. This is done be phophoratition of NAM. and releases undercapryl.
transpeptidase domain likinks the peptide chains of lipid two
vancomycin- binds to D-ala-Dala in PG peptide chain blocking PBP from working
b-lactams - prevent PBP from forming crosslinks- target transpeptidase domain
undercapnyl recycling
done after PBP gycotransferase domain connects the lipid 2 to the PG backbone
- it is dephophoratied so only one phospahte left and then it flips back into the cytoplam to be reused
Bacitracin
polysporne - binds to undecaprenyl pyrophospahte and prevents it from flipping back becuse it has not be dephosphorylated and makes the cell work harder to extend the PG layer
- blockes dephosphorylation
Lyzosomes
are in humans and bacteria
- used in bacteria for cell walkl remodleing
used in human for tears and stuff
they cleave the NAM-NAG bond
- they are most effective in gram positive since mostly in gram pos and think and gram neg still have outermemebrane
they two diamino acid in third position
meso-DAP or L-lysine
Transpeptidation mechanism
cross-links formed by PBP transpeptidase domain
1. PBP forms complex with peptide by removing one d-ala and then diamino acid reacts with the complz forming an amide bond
hwo do B lacatams work and antibiotic resistance
B lactans 4-membred ring binds to serine of the PBP
serine- B lactamases - degrade b lactams by hydrolying the four membared ring preventing it from binding to PBP
B-lactam resisitance and MRSA
MRSA encodes for PBP2a which is anlogus to PBP but it can not be targeted by b lactams
what bacteria does vancomycine work on
gram positive since it has more exposed d-ala-dala
- binds to d-ala-dla to prevent crosslinking
Vancomycin resistance
bacteria habve learned to chnage a d-ala group to either d-lac or d-ser, whule PBP can still form cross link vacomycin cant bind
