2-4: Bacterial Outer Membranes & More

Question 1

What gram status has an outer membrane

Answer 1

Gram negative

Question 2

What important molecule makes up the outer membrane

Answer 2

Lipopolysaccharide

Question 3

How do the compositions of the outer and inner OM leaflets vary

Answer 3

Outer = Some phospholipid, mostly LPS
Inner = phospholipid

Question 4

What are the three parts of LPS

Answer 4

1. Lipid A
2. Core polysaccharide
3. O-specific polysaccharide

Question 5

What is Lipid A

Answer 5

base of LPS, anchored into OM by hydrophobic tails. Phosphates with negative charge

Question 6

How is Lipid A related to the immune system

Answer 6

it is an endotoxin that can be sensed by the immune system, can lead to unchecked immune response (septic shock) if detected in blood stream

Question 7

What is the O-specific polysaccharide

Answer 7

Diverse sugar subunits, variable

Question 8

The OM is anchored to the CW via…

Answer 8

Braun’s lipoprotein

Question 9

How does braun’s lipoprotein anchor the OM and CW

Answer 9

Lipid is anchored in OM, covalently attached to peptidoglycan of CW

Question 10

Is the membrane permeable?

Answer 10

Impermeable to large molecules (proteins)
Permeable to small molecules

Question 11

How is the OM permeable

Answer 11

Porins (protein channels allow entrance/exit of small molecules)

Question 12

Are porins specific

Answer 12

Either or

Question 13

What are the functions of the OM

Answer 13

Mechanical strength
barrier (less than CM) but soaks up/blocks access
Important for antibiotic sensitivity
Protects cell wall
Enables periplasmic space

Question 14

The space between the OM and the CM is the…
In what gram state…

Answer 14

Periplasm, negative

Question 15

Is there a periplasm in gram positive cells

Answer 15

Kinda (space between CM and CW) but is small, function not clear

Question 16

What are the functions of the periplasm

Answer 16

Buffer btw environmental & cell
Break down macromolecules, take up as nutrients
High affinity binding proteins for nutrients
Detoxify harmful
Protein folding

Question 17

How does the periplasm aid in protein folding

Answer 17

Disulfide bond formation

Question 18

What is the S-layer

Answer 18

Rigid/permeable monolayer of of protein or glycoprotein
Outermost layer

Question 19

Function of the S-layer

Answer 19

Protective layer (from bacteriophages, host defenses)
Provide periplasmic space

Question 20

What are capsules and slime layers, what’s the difference

Answer 20

Coats of polysaccharides around cell surface
Capsule = organized into matrix, attached to the cell
Slime layers = loosely attached, less organized

Question 21

Function of capsules/slime layers?

Answer 21

Adhering to surfaces, protection from host immune cells, protection from water loss

Question 22

Protein filaments that extend from surface of the cell…

Answer 22

Pili

Question 23

Function of conjugative pili?

Answer 23

Conjugation (transfer of genetic material between bacteria via pilus bridge)

Question 24

Pilus that mediates attachment =

Answer 24

Fimbria