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Microbiology > PM and Cell wall > Flashcards

PM and Cell wall Flashcards

1
Q

How is bacterial PM composed?

A

50% lipid (among that 50% is phospholipids), 50% protein.

Bacteria:
2 Unbranched (Linear) FAs with ester linkage to glycerol and 1 phosphate.

PM not rich in sterols,

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2
Q

How is archaeal PM composed?

A

Branched isoprenoid chains with ETHER linkage to glycerol + 1 phosphate.
Unsaturated.
= Branched, unsaturated, Fatty alcohols!

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3
Q

How can bacterial PM lipid content differ?

A

Phosphatidic acid can be conjugated with Serine, Choline or Ethanolamine.

To form:
Cardiolipin (CL)

Phosphatidyl-ethanolamine (PE)

Phosphatidylglycerol (PG)

Gram -ve bacteria have more PE

Gram +ve have more PG and CL.

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4
Q

How can lipid content affect the charge of bacterial PMs?

A

Gram +ve have more PG and CL lipids

Gram -ve have more PE lipids.

PG is negatively charged, whilst PE is neutral.

Therefore, Gram -ve have more neutrally charged PE than Gram +ve which have more negatively charged PG

= Gram +ve have more negative PM.

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5
Q

How does Archaeal and bacterial PM differ>

A

Ether linkage of glycerol to 2 branched, isoprenoid, unsaturated Fatty Alcohols.

Some parts of archaeal PM is monolayer, where has very long fatty alcohol chains.
= Confers local lower fluidity and reduced permeability.

The branched, unsaturation of isoprenoid provides resistance to dissociation in hyperthermophilic archaea.

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6
Q

How does PM change with respect to temperature?

Unsaturation?

A

Lipid movements - rotation, chain rotation, lateral diffusion or flip-flop

Each membrane has transition temp - 50% of PM is fluid-like.

Longer chain FAs confer higher transition temperature.

Unsaturation gives lower transition temperature.

Archaeal PM have unsaturation, but can have v. long chain Fatty aclohols.

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7
Q

Are sterols found in bacterial PM?

Archaea?

A

MOST bacteria lack sterols.
except Spirochetes, Mycoplasma… = MOLLICUTES

Bacteria can have rafts - containing HOPANOIDS.

Archaea have no sterols/hopanoids.

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8
Q

How can sterols/Hoppanoids affect PM fluidity?

A

Sterols and hopanoids can act as fluidity buffer molecules - serve to rigidify membrane portions.

Especially important when lacking cell walls.
- MOLLICUTES - contain sterols and lack a cell wall.

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9
Q

What are extrinsic and intrinsic proteins?

A

Intrinsic proteins can be TM or anchored in PM.
= Strongly bound to PM, with TM proteins extending across 2 faces of envelope.
= NEEDS DETERGENT AND ORGANIC SOLVENTS TO REMOVE
= Lipidation, or transmembrane alpha helices/beta barrels…

Extrinsic proteins are weakly bound to PM, and can be only present on of 2 sides
= can have hydrophobic loops, electrostatic binding and in plane alpha helices to anchor..

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10
Q

What is the function of PM?

A

Highly regulated barrier of permeability and osmosis.

Transport systems for solutes like nutrients and ions.

Involved in energy generation - as bacteria lack mitochondria - can have respiratory/photosynthetic transport systems - ATP synthases in all, but maybe not always ETC.

Coordinate cell wall synthesis.

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11
Q

What antibiotics target the PM?

A

Bactericidal and detergent-like antibiotics

Polymixins - effective against both -ve and +ve

Daptomycin - against Gram +ve membranes which are enriched with PG

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12
Q

What are the obligatory structures in Bacteria and ARchaea?

A

Gram +ve = PM, thick peptidoglycan cell wall.

Gram -ve = PM, thin peptidoglycan cell wall, outer membrane

Mollicutes - PM

Archaea:

Gram +ve = PM, thick pseudomurein cell wall

Gram -ve = PM, and outer membrane.

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13
Q

What facultative structures cna be foundd in bacteria and archaea?

A

Gram +ve = can have an S layer and Polysaccharide capsule.

S-layer = glycoproteinaceous surface monolayer…

Gram -ve = S layer and capsule

Mollicutes = capsule

Archaea do not have capsules, but can both have S layer.

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14
Q

How does Gram staining work?

A

Crystal violet enters cytoplasm.

Mordant fixes colour

Alcohol is decoloriser, passing into cell to remove crystal violet.

Thick peptidoglycan cell wall blocks alcohol entry in Gram +ve
= purple

Add Safranin counterstain = pink Gram -ve

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15
Q

What can be found in bacterial cell wall?

A

Gram -ve:

PM, then lipoproteins can be found in periplasmic space.

Thin peptidoglycan layer

Outer membrane, then LPS with porins.

Gram +ve:
PM, with lipoteichoic acids and teichoic acids, with lipoprotein.
Thick peptidoglycan layer.

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16
Q

What is the composition of peptidoglycan?

A

N-acetylglucosamine (NAG),
N-acetyl muramic acid (NAM)
Alternating NAG-NAM glycans joined with Beta 1,4-glycosidic bonds.

Glycan chain NAMs are linked with lateral, tetrapeptide chains and peptide interbridges or Interpeptide bonds.

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17
Q

How are glycan chains linked in Gram +ve or Gram -ve chains?

A

Glycan chain NAMs are linked with lateral, tetrapeptide chains and peptide interbridges or Interpeptide bonds.

Gram -ve bacteria like E.Coli have Interpeptide bonds.
DAP and D-ALA of NAM tetrapeptide chains.

Gram +ve bacteria have INTERPEPTIDE BRDGES
Additional glycine residues on NAM link to Lysine of other NAM.

18
Q

What is the general outline of the stages of Cell wall synthesis?

A

Cytoplasmic stage:
Synthesis of precursors, UDP-NAM-Pentapeptide and UDP-NAG.

Membrane stage:
Transport across PM with Lipid transporter

Lipid II-NAG-NAM-pentapeptide.

Parietal stage:
Bind to existing peptidoglycan.
Formation of inter-peptide bridges, with loss of terminal Alanine from NAM-pentapeptide.

19
Q

How are peptidoglycan chains assembled in the final stage of cell wall synthesis?

A

Parietal stage:

Cross-linking of peptidoglycan chains occurs via PBPs

Penicillin-binding proteins.

PBPs are ALL transpeptidases.

(some can bind NAG-NAMs are transglycolyases)

During transpeptidation, terminal D-Ala is removedto form tetrapeptide, linking D-ala and DAP to form interpeptide bond (Gram -ve)

20
Q

What classes of antibiotics target cell wall?

A

Beta lactams:
Penicillins, cephalosporins, carbapenems, monobactams….

Glycopeptides - Vancomycin, teicoplanin

Fosfomycin

= ALL BACTERICIDAL!!!

21
Q

What is the MOA of beta-lactams?

A

FIxation to PBPs - inhibition of transpeptidation.
= Prevents cross-link formation during terminal, parietal stage of cell wall synthesis.

22
Q

How do glycopeptides work?

A

Against cell wall synthesis.

= Vancomycin, teicoplanin

Inhibition of peptidoglycan synthesis.

Formation of complex with D-ala-D-ala peptidyl residues of peptidoglycan precurssors after emerging from PM.

23
Q

What is MOA of Fosfomycin?

A

Prevent formation of NAG:
Inhibition of Pyruvate-NAG transferase.
= Prevents NAG precursor synthesis and therefore peptidoglycan synthesis,

24
Q

What is lysozyme?

A

Lysozyme is an acid hydrolase - hydrolyses Beta-1,4 glycosidic bonds between NAG and NAM in peptidoglycan chains.

Present in secretions like tears, mucus, saliva.

25
Q

Why is the cell wall an important antibiotic target?

A

Provides mechanical resistance to osmotic pressure.
= In a hypotonic solution, osmosis into cell will lead to increased osmotic pressure.

Maintenance of cell shape/morphology.
= Rod-shape in E.coli can be lost when treated with penicillins.
= Morphology important to preventing amoeba digestion.

-Fixation of bacteriophage and adhesion in Gram +ve.

26
Q

What are specific components to Gram +Ve cell wall?

A

THICK peptidoglycan layer.

Teichoic and Lipoteichoic acids:

NO LPS

May have a facultative polysaccharide capsule and S-layer.

27
Q

What are Teichoic acids?

A

Gram +ve bacteria.

Polyalcohol of glycerol and ribitol intersperesed with phosphates, which are conjugated by AA residues.
E.G Glucose, NAG, D-ala

The attached residues can vary between bacterial speciesi.

Becomes Lipoteichoic acid when a lipid moiety is attached at extremities.

28
Q

What is the function of Teichoic acids?

A

Surface adhesion - to biofilms, to host cells.

Antigenic properties - can be recognised by macrophages.

Anchorage of peptidoglycan.

Regulation of extracellular cation concentration (as has phosphates)

29
Q

What are specific components to Gram -ve bacteria cell wall?

A

OUTER MEMBRANE = phospholipid bilayer.

Braun’s Lipoproteins.
LPS
Porins

30
Q

How is Gram -ve bacterial cell wall composed?

A

Braun lipoproteins help to anchor the cell wall with the outer and inner membrane.

(as thinner than Gram +ve, less sturdy).

Porins - enable passive transport, antibiotic entry…

LPS on outermembrane.

Thin peptidoglycan layer.

31
Q

What is the structure of LPS?

A

Lipid A, with a core polysaccharide and then a Lateral chain called O-antigen.

Lipid A anchors into outer membrane, contains fatty acids, NAG and phosphates.
= 6 FA chains.
(ENDOTOXIN!!!)

Core polysaccharide, contains some sugars and KDO - consistent.

O-antigen - variable long chain of sugars.
= Recognised by immune system.

32
Q

What is the function of LPS?

A

Lipid A acts as an endotoxin.

Component of outer membrane.

O antigen is recognised by macrophrages.

Can be recognised and fixated to by Bacteriophages.

Acts as adhesins during biofilm formation.

Lipid A activates TLR4 -

33
Q

Is there porin diversity?

A

Porins can diffuse alcohols, sugars, nutrients etc.

Import siderophores - Iron fixation.

Act to efflux antibiotics, toxins etc.

ADHESION

34
Q

How can transport across both membranes of Gram -ve be coupled?

A

Maltose serves as example.

Maltose diffuses through LamB porins in outer membrane.

MalE attachment for periplasmic transport.

Active transport, using ATP hydrolysis, via Mal-FGK.

Also glycerol Active Transport too…

35
Q

How can cell wall weight differ between Gram +ve and Gram -ve?

A

Gram +ve cell wall acounts for 40% of dry weight.

Around 10% of dry weight.

36
Q

What bacteria do not have a cell wall?

A

NOT PRESENT IN MOLLICUTES.

E.G mycoplasma, phytoplasma.

Instead, some may have facultative polysach. capsule.

Would appear pink (gram -ve) in Gram staining.

Evolved to lose Cell wall from Gram +ve bacteria.

= RESISTANT TO penicillins and lysozymes etc.

37
Q

What is the structure of Archaeal cell walls?

A

Archea always have an S-layer above cell wall.

Can be Gram +ve or Gram -ve.

BUT NOT PEPTIDOGLYCAN.

38
Q

What is Gram +ve archaea?

A

PM, then a layer of Pseudomurein, then S-layer.

Psuedomurein layer anchors S-layer, because Gram +ve S-layer are not anchored to PM/TM.

= Stains purple in Gram +ve

39
Q

What is Gram -ve archeae?

A

Large PM anchored glycoproteins form S-layer.

Glycoproteins are TM, with globular heads forming S-layer.

  • Forming a monolayer.

S-layer self assembles from monomers to form a almost crystalline structure.

= RELATIVELY RESISTANT + ABLE TO COLONISE HOSTILE ENVIRONMENTS>

40
Q

What is the S-layer in Archaea?

A

S-layer self assembles from monomers to form a almost crystalline structure monolayer.

= RELATIVELY RESISTANT + ABLE TO COLONISE HOSTILE

In Gram -ve, glycoproteins are large, anchored in PM. But in Gram +ve, they are anchored to pseudomurein layer.

41
Q

What is Pseudomurein?

A

Acetyl-alosaminuronic acid and acetyl-glucosamine
linked with Beta, 1-3 glycosidic bonds.

Forming a glycan chain.

Glycan chains are linked through tetrapeptides and a peptide bridge.

42
Q

What is role of archaeal envelope?

A

Mechnical resistance ot osmotic pressure.

Maintenance of cell shape and morphology.

Surface adhesion.

Provide some resistance to hsotile environemtsn as S-layer forms cyrsalline-like monolayer.

Microbiology (9 decks)

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