Bacterial Cell Envelope Flashcards
What is found in the cell envelope?
Plasma membrane (lipid bilayer), peptidoglycan cell wall, & envelope proteins
Explain the Gram positive cell envelopes?
Thick peptidoglycan layer, single membrane, lipoteichoic acid polymer (embedded in membrane), & teichoic acid (anchored to cell wall)
Explain the Gram negative cell envelope?
Thin peptidoglycan layer, inner & outer layer membrane, LPS (endotoxin) surface polymer in outside membrane
Explain the mycobacterial cell envelope ?
Thin peptidoglycan, single membrane, outer layer of mycolic acid (hydrophobic - prevent influx of antibiotics & toxic m/os - similar function to 2nd membrane) - arabinogalactan links peptidoglycan to mycolic acid
Explain the cell envelope of wall-less bacteria?
No peptidoglycan synthesis - obligate as must live in osmotically balanced environment
What are the most common forms of cell envelopes?
Gram positive, Gram negative. mycobacterial, & wall-less
Explain the Gram stain?
1880s - Hans Christian Joachim Gram - distinguish between Streptococcus pneumoniae (+) & Klebsiella pneumoniae (-) - Crystal violet (+ve) binds to peptidoglycan via -ve polymers of LPS & teichoic acid, iodine complexes with crystal violet - trapper (prevents it being washed away), 95% ethyl alcohol decolourises Gram -ve bacteria via interactions with outer membrane, safranin binds to associated polymers of peptidoglycan (pink)
Gram stain visualisation?
Gram +ve = purple
Gram -ve = pink
Explain the Ziehl-Nielsen stain?
Mycobacteria - hydrophobic mycolic acid makes Gram staining impossible - carbol fuchsin (pink), phenol, & heat allow penetration of mycolic acid layer & binds with -ve mycolic acid- counterstain is added
What is the problem with taking colistin?
Disrupts bacterial & human membranes
Explain the cell membrane in bacteria?
Permeability barrier, protein anchor, energy conservation - selective permeability (entry & exit of dissolved material, transport large & charged molecules via carrier proteins), ATP & essential co-factor generation via membrane bound proteins
Explain the structure of bacteria & archaea cell membrane?
Hydrophilic region - glycerol, phosphate, ethanolamine
Hydrophobic region - fatty acids
majority are straight chain fatty acids densely packed - branching allows substance to enter (decrease in response to antimicrobials)
Archaea - more branching - lipids sometime bind to each other - more fluid characteristics
Explain the function of the cell wall of bacteria?
Strength, contain membrane, capture high conc. of soluble material, contain osmotic pressure up to 208kPa, anchor for surface molecules, target of betalactams
Explain the structure of peptidoglycan in the bacterial cell wall?
Mesh-like layer - repeated disaccharides form a polysaccharide backbone (N-acetylmuramic acid (NAM) & N-acetylglucosamine (NAG)) cross-linked of stem peptides on NAM molecules (position 3 to position 4) - gycosidic bonds in x axis & peptide bonds in y axis
GRAM +: indirect linkage L-lysine & d-alanine via pentaglycine bridges
GRAM -: direct linkage between meso-diaminopimelic acid (DAP) to d-alanine
What is pseudopeptidoglycan?
Made of G (n-acetylglucosamine) & T (n-acetyltalosaminuronic acid) - L-lys to L-glu - found in archaea
What are membrane proteins?
Hydrophobic domains span membrane & hydrophilic domain (Cytoplasmic & ECF) - integral (significantly embedded) & peripheral (slightly attached e.g. lipoprotein)
What are the major forms of transport?
1) Osmosis - diffusion of water across membrane
2) Diffusion - movement of particles from area of high conc. to low conc.
3) Active transport - movement of particles against conc. gradient
What is teichoic acid?
Polymer of repeated sugar - Gram +, high amount of phosphate (-ve) attracts +ve antimicrobials & immune cell
Explain lipopolysaccharide?
Endotoxin - Gram -ve - Lipid A (hydrophobic domain (endotoxin)) ,core oligosaccharide (non-variable core), & O-antigen (repeat hydrophilic distal polysaccharide- varies- dictate host range & how they colonise)
What is the s-layer?
self-assembling 2D protein arrays - some bacterial & all archaea - anchored non-covalently to LPS or teichoic acid
What are fimbriae & pili?
Hair-like proteinaceous attachment on surface
What is the capsule/glycocalyx?
Gelatinous polysaccharide layer, cover cells - form biofilms - hydrophilic (90% water) - protect against phagocytes - diverse (dictate serotype of m/o)
Explain active transport?
Simple transport uses H+ ions to facilitate transport - Antiporter (opposite direction to H+ outisde cytplasm) & symporter (Same direction as H+) - lactose transport
Explain the ABC Transport System?
3 components - substrate binding protein (periplasm), transmembrane transporters, ATP hydrolysing enzyme (cytoplasm) - maltose transport
Explain the phosphotransferase system?
Group translocation, multiple enzymes, substances are chemically altered e.g. dephosphorylation of pyruvate to enter TCA cycle & phosphorylation of glucose required for entry into glycolysis - glucose transport
