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

Question 1

The outer membrane

Answer 1

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

• outer leaflet

Question 2

Outer leaflet

Answer 2

Composed of molecules called LPS

It’s the predominant feature of the outer membrane

Question 3

Lipopolysaccharide (LPS) three parts

Answer 3

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

Question 4

Lipid A

Answer 4

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.

Question 5

Are lipid A and phospholipids the same

Answer 5

NO

Question 6

O-specific polysaccharide (“O antigen”) are

Answer 6

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

• Repeating combination of sugars with variable numbers of repeat

Question 7

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

Answer 7

Variable - species have hundreds of versions

Question 8

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

Answer 8

LPS with very little phospholipid.

Question 9

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

Answer 9

phospholipid. asymmetrical

Question 10

The outer membrane is anchored to the

Answer 10

Cell wall

Question 11

Braun’s lipoprotein serves to

Answer 11

connect the OM to cell wall

Question 12

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

Answer 12

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

• Very common in Gram negative cells.

Question 13

The OM contains

Answer 13

Porins

Question 14

Porins are

Answer 14

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

• can be specific or non specific

Question 15

Functions of the outer membrane

Answer 15

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

Question 16

Periplasmic space (“periplasm”)

Answer 16

Space between cytoplasmic/outer membranes of Gram negative

bacteria

Question 17

Periplasmic space function

Answer 17

Buffer between environment and cell

Question 18

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

Answer 18

Gram positive

Question 19

Periplasmic space (“periplasm”) FUNCTIONS and PROTEINS

Answer 19

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

Question 20

S-layers

Answer 20

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

• outermost layer

Question 21

S-layer functions

Answer 21

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

Question 22

Capsules and slime layers functions

Answer 22

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

Question 23

Capsules are organized into a

Answer 23

matrix and attached to the cell

Question 24

slime layers are

Answer 24

loosely attached, less organized

Question 25

Pili (singular = pilus) are

Answer 25

protein filaments that extend from the surface of a cell

Question 26

Where are pilus found mostly

Answer 26

Gram -

Question 27

Different pili have different

Answer 27

Functions

Question 28

Conjugation pili

Answer 28

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

Question 29

Fimbria is a term used for a pilus that

Answer 29

mediates attachment (to a surface or
another cell)