Bacterial Outer Membrane, Periplasm and More

Question 1

the outer membrane

Answer 1

-gram negative only
second membrane outside the cell wall that is very different from the cytoplasmic membrane
-outer leaflet has LPS

Question 2

assymetry of the outer membrane

Answer 2

-the outer leaflet is mostly LPS with very little phospholipid
-the inner leaflet is comprised of phospholipid
-due to these two things it is asymmetrical

Question 3

lipopolysaccharide

Answer 3

-predominant feature of the outer membrane
-3 parts: lipid A within the membrane, core polysaccharide, O specific polysaccharide (outermost component)

Question 4

Lipid A

Answer 4

-very different from phospholipids
-hydrophobic tails anchor Lipid A in outermembrane
-phosphates confer a negative charge
-molecules can vary but overall structure maintained
-lipid A is also known as an endotoxin

Question 5

O specific polysaccharide

Answer 5

-comprised of diverse sugar units connected and branched in different ways
-repeating combination of sigars with variable numbers of repeats
-usually conserved within a given strain but highly variable from strain to strain
-detecting O antigen using specific antibodies can be used to identify a bacterium (serovar O antigen in Ecoli O157)

Question 6

Brauns lipoproteins

Answer 6

-connect the outer membrane to the cell wall
-small lipoprotein
-lipid anchors in outermembrane other end is covalently attached to peptidoglycan
-very abundant in Gram negs

Question 7

porins

Answer 7

-in outer membrane
-makes the outer membrane permeable to many small molecules
-porins are protein channels that serve as channels for entrance and exit of small molecules
-can be specific or non specific

Question 8

functions of the outer membrane

Answer 8

-provides mechanical strength through ionic bonds between adjacent LPS molecule via divalent metal ions
-can be an important barrier and is important for antibiotic sensitivity
-far more permeable than cytoplasmic membrane
-protects cell wall
-enables a substantial periplasmic space

Question 9

the periplasm

Answer 9

-in gram negative bacteria it is the space between inner and outer membranes
-smaller space in gram positive and function is not clear in gram positive
-space between cytoplasmic membrane and cell wall
-buffer between environment and cell

Question 10

the periplasm important proteins and functions

Answer 10

-break down macromolecules for uptake as nutrients
-high affinity binding protein for nutrients
-detoxify harmful compounds
-protein folding -disulfide bond formation

Question 11

S layers

Answer 11

-some bacteria, more common in archaea
-rigid/permeable monolayer of protein or glycoprotein
-self organized into repeating structre that encompasses the cell
-always the outermost layer of the cell
-can perform many of the same functions as the cell wall
-often protection from bacteriophage or pathogens of bacteria
-can provide periplasmic space or keep external proteins from accessing OM or cell wall

Question 12

capsules and slime layer

Answer 12

-coats of polysaccharide around cell surface
-capsules organized into matrix and attached to the cell
-slime layers are loosely attached and less organized
-adheerance to surfaces, protection from host immune cells and protection from dehydration

Question 13

pili and fimbriae

Answer 13

-protein filaments that extend from the surface of the cell
-particular to gram negative
-different pili have different functions
-fimbria are shorter and more plentiful

Question 14

conjunctive pili

Answer 14

-important for conjugation (transfer of genetic material between bacteria via a pilus bridge)

Question 15

fimbriae function

Answer 15

-mediates attachment to a surface or another cell