Thee Bcaterial Cell Envelope Flashcards
Majority of bacterial envelopes consist of?
- Plasma Membrane (lipid bilayer)
- Peptidoglycan (Cell wall)
- Envelope proteins
Gram Pos VS Gram Neg - bacterial envelopes
Gram pos
-Thick peptidoglycan layer
-Single membrane
-Lipotechoic and Techoic acid polymers
Gram neg
-Thin peptidoglycan layer
-Inner membrane and outer membrane
-LPS (endotoxin) surface polymer
What are 2 types of bacterial envelopes?
Mycobacterial and wall less
What does Mycobacterial envelope consist of?
-Thin peptidoglycan layer
-Single membrane
-Mycolic acid layer (hydrophobic)
-Arabinogalactan links peptidoglycan and mycolic acids
What do Wall-less bacterial envelopes consist of?
-No peptidoglycan synthesis
-Must live in osmotically balanced environment
Who was the gram stain developed by and in what year?
Hans Christian Joachim Gram in 1880
What was the gram stain initially used to distinguish between?
Streptococcus pneumoniae (gram pos) and Klebsiella pneumomiae (gram neg)
What are the 4 additions used in the gram stain
- Crystal Violet
- Iodine
- 95% Ethyl Alcohol
- Safranin
What happens at the addition of crystal violet and iodine?
-Positively charged crystal violet binds to negatively charged molecules - techoic acids of Gram pos and LPS of gram neg
-All bacteria are stained purple
-Iodine complexes with crystal violet and acts as a ´trapper´
What happens after the addition of Ethyl Alcohol?
-Decolouriser reagent
-Solubilises membranes
-Gram neg outer membrane stripped away including LPS and associated crystal violet
What happens after the addition of Safranin?
-Acts as a counterstain
-Binds to peptidoglycan and associated polymers of both gram neg and gram pos bacteria
-CV coloration overpowers Safranin in gram pos
What colours are gram neg or gram pos bacteria after the gram stain?
Gram pos are blue to purple
Gram neg are red to pink
Why is Gram staining impossible in Mycobacteria?
Because of the hydrophobic mycolic acid layer
What is used instead of gram stain for Mycobacteria?
Ziehl-Nielsen Staining uses carbol-fushin (pink stain), phenol and heat to allow penetration of mycolic acid layer.
Carbol-fushin associates w neg charged components of cell envelope including mycolic acids
What are the functions of the cytoplasmic membrane?
-Permeability barrier
-Protection anchor
-Energy conservation - ATP and essential co-factor generation is dependent on membrane bound proteins
What are the 2 key regions of membrane lipids?
-Hydrophilic region
-Hydrophobic region
What are examples of hydrophilic lipids?
-Glycerol
-Phosphate
-Ethanolamine
What is an example of hydrophobic lipid in membrane?
Fatty acids
Functions/Features of the cell wall (peptidoglycan)
-Forms mesh structure that gives strength to cell envelope
-contains plasma membrane
-captures high conc of soluble molecules by acting as a sponge
-able to contain osmotic pressure up to 208kPa
-acts as anchor for surface molecules e.g proteins and polymers
-Major target for antibiotics due to essential for survival of bacteria
What is the difference between peptidoglycan structures between pos and neg bbacteria
Gram pos= THICK
Gram neg= THIN
What are the repeating disaccharides that form the polysaccharide backbone in peptidoglycan?
NAM - N-Acetylmuramic acid
NAG - N-Acetylglucosamine
Joined by glycosidic bonds
What is the name given to amino acids attached to NAM? and what gives the structural rigidity to the cell wall?
´Stem-peptide´
Crosslinking between adjacent polysaccharide strands
What positions are bonded in stem peptide crosslinking in bacteria and archaea?
Position 3 to position 4 peptide bond
What is the diff betwen the stenm peptide linkage in Gram Pos and Gram Neg bacteria?
Gram Neg - direct linkage between meso-diaminopimelic acid (DAP) to D-alanine
Gram Pos - indirect linkage between L-lysine and D-alanine using a pentaglycine bridge
How can active transport be achieved?
- Simple transporters
2.Group translocation (TAT and PES systems) - ABC transporters
How do Simple Transporters facilitate the transport of molecules and what are examples of these?
-Simple transporters use H+ ions to facilitate transport of molecules into and out of the cell
i) Antiporter - Sodium proton antiporter- Transported molecule moves in opposite direction to H+ to outside cytoplasm
ii) Symporter -Lac permease- Transported molecule moves in same direction as H+ into the cell
Group translocation - Phosphotransferase system- PTS system
-Requires multiple enzymes
-Transported substances are chemically modified - phosphoralated or dephosphorylated
-E.g dephosphorylation of pyruvate required for entry into TCA cycle,
What is the ABC transporter system and what are the 3 components it requires?
Large family of transporters with a wide target molecule range
- Sustrate binding protein (Periplasm/extracellular)
- Transmembrane transporter
- ATP - hydrolysing enzyme (cytoplasm)
What is the bacterial membrane essential for?
Energy synthesis and conservation
What are techoic acids?
Simple polymers of repeating sugar units which decorate Gram pos cells
What are the 2 major types of techoic acids?
- Wall Techoic Acids (WTA) - Covalently linked to peptidoglycan
- Lipoteichoic acid - Attached to plasma membrane
What are Lipoglcan molecules?
-Lipoglycans found as part of outer memebrane of Gram neg bacteria
-Negatively charged
What do lipoglycans consist of?
-Lipid A - hydrophobic domain (exotoxin)
-Core oligosaccharide - hydrophyllic non-variable core oligosaccharide.
-O-antigen - Repeating hydrophilic distal polysaccharide
What is the S layer?
-2-D Protein layer on outer membrane or peptidoglycan
-Anchored non-covalently through interactions with LPS in gram negs and wall techoic acid in gram pos
What is the capsule?
-Gelatinous polysaccharide lavers which cover bacterial cells
-Hydrophilic
-During infection capsule polysaccharide inbibits phagocytosis
