2-4: Bacterial Outer Membranes & More

Question 1

Does gram positive or negative have an outer membrane

Answer 1

Gram negative

Question 2

What important molecule makes up the outer membrane in Gram negative bacteria

Answer 2

Lipopolysaccharide

Question 3

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

Answer 3

Outer = Liittle 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

contains 6 fatty acid tails and phosphates with negative charge. actual molecule varies depending on species

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

polysaccharaide made of diverse sugar subunits with a repeating combination of sugars, branched in different ways

Question 8

how does the O-antigen vary between/within species?

Answer 8

usually conserved within the same STRAIN (eg. E. coli O157 serovar), but species can have different antigens

Question 9

The OM is anchored to the CW via…

Answer 9

Braun’s lipoprotein

Question 10

Braun’s lipoprotein is only found in gram positive or negative?

Answer 10

negative

Question 11

How does braun’s lipoprotein anchor the OM and CW

Answer 11

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

Question 12

Is the membrane permeable?

Answer 12

Impermeable to large molecules (proteins)
Permeable to small molecules

Question 13

Why is the OM permeable

Answer 13

Contains porins (protein channels allow entrance/exit of small molecules)

Question 14

How are porins regulated?

Answer 14

Depending on expression

Question 15

What are the functions of the OM

Answer 15

Mechanical strength (due to ionic bonds between LPS and metal cations)
barrier (less than CM)
Important for antibiotic sensitivity
Protects cell wall (from lysozymes)
Enables periplasmic space

Question 16

The space between the OM and the CM is the what?
In what gram bacteria?

Answer 16

Periplasm, negative

Question 17

What are the functions of the periplasm

Answer 17

Buffer b/w environment & cell
Break down macromolecules, take up as nutrients
High affinity binding proteins for nutrients
Detoxify harmful compounds
Protein folding (disulfide bonds only form in oxidizing environments)

Question 18

Describe the cell wall in Gram positive bacteria

Answer 18

Smaller space between the cell membrane and cell wall, importance less clear

Question 19

The periplasm is the space between which two components?

Answer 19

Cytoplasmic membrane and cell wall - the space between outer membrane and cell wall is unknown

Question 20

What is the S-layer

Answer 20

Rigid/permeable monolayer of of protein or glycoprotein
Always the outermost layer

Question 21

Function of the S-layer

Answer 21

Protective layer (from bacteriophages, host defenses), Provide periplasmic space, prevent external proteins from accessing the OM

Question 22

What are S layers most commonly found in?

Answer 22

Bacteria, but more commonly archaea

Question 23

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

Answer 23

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

Question 24

Function of capsules/slime layers?

Answer 24

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

Question 25

What are pilli?

Answer 25

Protein filaments that extend from surface of the cell

Question 26

What type of bacteria produce pili?

Answer 26

Most bacteria, but particularly gram -

Question 27

Function of conjugative pili?

Answer 27

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

Question 28

What is Fimbria?

Answer 28

Pilus that mediates attachment