Bacterial Cell Envelope Flashcards
What are bacterial envelopes
Multilayered protective structures which provides protection against hostile external environment
What do the majority of bacterial envelopes consist of (3)
- Plasma membrane (lipid bilayer)
- Peptidoglycan (cell wall)
- Envelope proteins
Components of the bacterial cell envelope are targets for what
Antibiotics
Features of gram pos bacterial envelope
- Thick peptidoglycan layer -> increased turgor pressure
- Single membrane
- Lipotechnoic & Technoic acid polymers
Features of gram neg bacterial envelope
- Thin peptidoglycan layer
- Inner membrane & outer membrane
- Lipopolysaccharide (endotoxin) surface polymer
Features of mycobacterial bacterial envelope
- Thin peptidoglycan layer
- Single membrane
- Mycolic acid layer (hydrophobic)
- Arabinogalactan links mycolic acids and peptidoglycan
Features of wall-less bacterial envelope
- No peptidoglycan synthesis
- Must live in osmotically balanced environment
When & by who was the Gram Stain developed
In the 1880s by Hans Christian Joachim Gram
Function of Crystal Violet during gram stain
- Pos charged
- Binds to petidoglycan & neg charged polymers -> Teichoic acids & LPS
Function of Iodine during gram stain
- Complexes w crystal violet
- “Trapper” reagent -> prevents crystal violet being washed away in further steps
Function of 95% Ethyl Alcohol during gram stain
- Decolouriser reagent
- Removes any dyes from lipid membrane
Function of Safranin during gram stain
- Counterstain
- Binds to peptidoglycan & associated polymers to give pink colour
Gram Pos gram stain resulting colour
Purple
Gram neg gram stain resulting colour
Pink
What feature of Mycobacteria makes gram staining impossible
The hydrophobic mycolic acid layer
3 functions of the plasma membrane
- Permeability barrier - prevents leakage, gateway fro transport of nutrients
- Protein anchor - site of proteins that participate in transport, chemotaxis
- Energy conservation - site of generation & dissipation of proton motive force
What is the plasma membrane completely impermeable for
Ions
They require transport proteins
Components of the hydrophilic region of the phospholipid bilayer of the plasma membrane
- Glycerol
- Phosphate
- Ethanolamine
What are the components of the hydrophobic region of the phosphlipid layer
Fatty acids
Which have the more branched fatty acids chain; bacterial lipids or archaeal lipids
Archaeel lipids have more branched chains of fatty acids -> can be more fluid
What does peptidoglycan consist of
- Amino acids (peptido)
- Repeating units of carbohydrates (glycan)
Cell wall functions (6)
- Structural strength to cell envelope
- Contains the plasma membrane
- Captures high concentrations of soluble molecules (nutrients etc) by acting like a sponge
- Contains osmotic pressure up to 208kPa
- Anchor for surface molecules - proteins & polymers
- Target for antibiotics
What kind of peptidoglycan do gram pos bacteria have
THICK
What kind of peptidoglycan do gram neg bacteria have
thin
What does petidoglycan consist of
- A repeating disaccharide forming a polysaccharide backbone
What does NAM stand for
N-Acetylmuramic acid
What does NAG stand for
N-Acetlyglucosamine
What gives structural strength to peptidoglycan layers
Crosslinking of amino acids on adjacent polysaccharide strands
What are AAs attached to NAM called
The stem peptide
What position bond is stem peptide crosslinking in bacteria & archaea
Position 3 to position 4 peptide bond
What is the major molecular difference between Gram pos and neg peptidoglycan (GRAM NEG)
- Position 3 on the stem peptide
- Gram neg stem peptide linkage is a direct linkage between meso-diaminopimelic acid (DAP) to D-alanine
What is the major molecular difference between Gram pos and neg peptidoglycan (GRAM POS)
- Position 3 on stem peptide
- Gram pos stem peptide linkage is indirect between L-lysine and D-alanine, using a pentaglycine bridge
Osmosis
The diffusion of water across a membrane
Diffusion
The movement of particles from an area of high conc to an area of low conc
Active transport
Movement of particles against a concentration gradient
What do simple transporters use to facilitate transport of molecules in & out of the cell
They use H+ ions
How does an ANTIPORTER work
Transported molecule moves in the opposite direction to H+ to outside the cytoplasm
How does a SYMPORTER work
Transported molecule moves in the same direction as the H+ ion, into the cell
The phosphotransferase system (PTS system) is an exzmple of what kind of transport
Group translocation
What happens in the phosphotransferase system
- Requires multiple enzymes
- Transported substances are chemically modified (glucose is phosphorylated, pyruvate is dephosphorylated)
The 3 components the ABC transporter system needs
- Substrate binding protein (in periplasm/extracellular)
- Transmembrane transporter
- ATP hydrolysing enzyme (in cytoplasm)
What are teichoic acids
Simple polymers of repeating sugar units which decorate gram pos cells
What are the 2 types of teichoic acid and where are they found
- Wall teichoic acid - covalently linked to peptidoglycan
- Lipteichoic acid - attached to plasma membrane
What do the lipopolysaccharides on gram neg outer membrane consist of
- Lipid A: Hydrophobic domain. Also known as an endotoxin!?
- Core Oligosaccharide: Hydrophilic non variable (same repeating sugars) core oligosaccharide
- O-antigen: repeating hydrophilic distal polysaccharide
What is the S layer
- Part of the envelope
- Protein layer on outer membrane or peptidoglycan
WHat is the S layer anchored to and with what bonds
Anchored non covalently through interactions with LPS in gram negs and wall teichoic acids in gram pos
What is the capsule
They are gelatinous polysaccharide layers which cover bacterial cells
FUnctions of capsule
- Prevents bacteria cells from desiccating in environment
- Keeps bacteria hydrated
- Inhibits phagocytosis during infection
