Topic 2-L5 - Bacterial Outer Membranes, periplasm and more Flashcards

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1
Q

The outer membrane

A

Gram negative bacteria have a second membrane outside the cell wall this is very different from the cytoplasmic membrane

  • outer leaflet
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2
Q

Outer leaflet

A

Composed of molecules called LPS

It’s the predominant feature of the outer membrane

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3
Q

Lipopolysaccharide (LPS) three parts

A

(1) lipid A (within membrane)
(2) core polysaccharide
(3) O-specific polysaccharide (outermost component)

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4
Q

Lipid A

A

Hydrophobic tails anchor Lipid A in OM

  • base of LPS o Phosphates confer a negative charge

Important molecule sensed by the immune
system. Also known as “endotoxin”. Can lead
to a potent and unchecked immune response – can cause septic shock if detected in
bloodstream.

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5
Q

Are lipid A and phospholipids the same

A

NO

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6
Q

O-specific polysaccharide (“O antigen”) are

A

Polysaccharide comprised of diverse sugar subunits connected and
branched in different ways

  • Repeating combination of sugars with variable numbers of repeat
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7
Q

O-specific polysaccharide (“O antigen”) are highly

A

Variable - species have hundreds of versions

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8
Q

The contemporary view is that the outer leaflet of the OM is mostly (or
almost exclusively)

A

LPS with very little phospholipid.

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9
Q

The inner leaflet is comprised of _____________. It is therefore___________.

A

phospholipid. asymmetrical

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10
Q

The outer membrane is anchored to the

A

Cell wall

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11
Q

Braun’s lipoprotein serves to

A

connect the OM to cell wall

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12
Q

Small lipoprotein (protein modified to be linked to lipids) –

A

lipid anchors in OM, other end of protein covalently attached to peptidoglycan.

  • Very common in Gram negative cells.
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13
Q

The OM contains

A

Porins

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14
Q

Porins are

A

protein channels that serve as channels for entrance/exit of small molecules

  • can be specific or non specific
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15
Q

Functions of the outer membrane

A
  • mechanical strength (ionic bonds between LPS molecules)
  • serves as barrier (still permeable)
  • protects cell wall
  • enables periplasmic space
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16
Q

Periplasmic space (“periplasm”)

A

Space between cytoplasmic/outer membranes of Gram negative

bacteria

17
Q

Periplasmic space function

A

Buffer between environment and cell

18
Q

Periplasmic space (“periplasm”) is much smaller space between cell membrane and the cell wall in

A

Gram positive

19
Q

Periplasmic space (“periplasm”) FUNCTIONS and PROTEINS

A
  • Break down macromolecules for uptake as nutrients
  • High affinity binding protein for nutrients
  • Detoxify harmful compounds
  • Protein folding - disulfide bond formation
20
Q

S-layers

A

Rigid/permeable monolayer of protein or glycoprotein – self- organized into a repeating structure that encompasses the cell

  • outermost layer
21
Q

S-layer functions

A
  • same functions as cell wall
  • protective layer
  • keep external proteins from accessing OM or cell wall
22
Q

Capsules and slime layers functions

A
  • adhering to surfaces
  • protection from host immune cells (bacterial pathogens)
  • protection from water loss/dehydration
23
Q

Capsules are organized into a

A

matrix and attached to the cell

24
Q

slime layers are

A

loosely attached, less organized

25
Q

Pili (singular = pilus) are

A

protein filaments that extend from the surface of a cell

26
Q

Where are pilus found mostly

A

Gram -

27
Q

Different pili have different

A

Functions

28
Q

Conjugation pili

A

important for conjugative (transfer of genetic material between bacterial via a pilus bridge)

29
Q

Fimbria is a term used for a pilus that

A
mediates attachment (to a surface or
another cell)