Gram Negative Walls

Question 1

What are the functions of the Prokaryotic cell wall?

Answer 1

• defines cell structure
• protects against osmotic lysis
• contributes to pathogenesis often therefore it is the site of many antibiotics

Question 2

what type of bacteria has an advantage to many antibiotics

Answer 2

Mycoplasma bacteria because they do not have a cell wall. Same with eukaryotes

Question 3

What is the composition of Gram positive layers

Answer 3

• PM plus a thick electron dense thick layer
• thick peptidoglycan layer
• has techoic acids

Question 4

What is the composition of Gram negative layers

Answer 4

• PM
• thin peptidoglycan layer
• OM

Question 5

True or false, Archaea have no cell walls

Answer 5

False they have diverse cell walls but they have NO PEPTIDOGLYCAN

Question 6

What type of bacteria have sterols inside their cytoplasmic membrane?

Answer 6

Mycoplasma!! for stability since they lack cell walls. They are osmotically sensitive.

Question 7

what are the 4 reagents of a gram stain? What order are they applied?

Answer 7

1) Primary stain - crystal violet
2) mordant - Grams iodine
3) decolourize reagent - acetone
4) counter-stain - Safranin

Question 8

What colour do Gram positive and negative bacteria appear As?

Answer 8

(+) - violet

(-) - pink

Question 9

E. Coli and Staph epidermidis are examples of +/-?

Answer 9

E. Coli is gram negative

Staph is gram positive

Question 10

Extending from the peptidoglycan layer, what 3 proteins are seen in gram negative bacteria?

Answer 10

1) LPS (lipopolysaccharides) extend at very surface
2) Porins exist in the phospholipid OM
3) Brauns Lipoprotein which connects Peptidoglycan with OM

Question 11

What is the purpose of the OM

Answer 11

• keeps periplasm inside cell
• has many toxic properties
• chemically distinct from PM
• permeable to Di-saccharides due to PORINS

Question 12

What protein is responsible for the OM’s toxic behaviour? Where is it located?

Answer 12

Lipopolysaccharides!!
They are only found on GRAM NEGATIVES
they are unsymmetrically on the outer leaflet of the OM and cover 40% of cell surface
3-9% dry weight of cell!!
very toxic

Question 13

What is Endotoxin?

Answer 13

term doctors use for LPS

Question 14

What are a few illnesses known to be caused by endotoxins?

Answer 14

Diarrhea
fibrinolysis
Pyrogenic (induces fever)

Question 15

If someone were infected by a Gram positive endotoxin what may be the symptoms

Answer 15

none, gram positives do not have LPS

Question 16

What are the components of LPS?

Answer 16

Lipid A, a Core, and O-antigenic side chain

Question 17

True or false, cells that cannot make the base structure of LPS are not viable

Answer 17

True, If a cell cannot make Lipid A and the first few structures of the core called KDO then they will not survive!

Question 18

Explain Lipid A

Answer 18

• 6-7 fatty acids connected to a phosphorylated glucosamine
• the reason why LPS is toxic
• Fatty acids are either directly linked to GA or ether linked to 3’OH fatty acids on GA already

Question 19

Explain LPS’s Core

Answer 19

connected to Lipid A at 6th position of glucosamine. built with 8-10 unusual sugars, often phosphorylated and branched.

Question 20

what sugars are in the LPS core? What sugar connects the core to Lipid A?

Answer 20

KDO, heptose, and other normal ones

KDO IS RESPONSIBLE FOR CONNECTION TO LIPID A

Question 21

Explain LPS’s O-antigenic side chain

Answer 21

• made up of hydrophilic sugars and amino acids in groups of 3-5 which are polymerized 30 ish times
• this is what your body develops antibodies too

Question 22

Explain LPS synthesis

Answer 22

The entire protein is made inside the cytoplasm and has to be transported together
the formation is strictly sequential from lipid A
e.g the side chain cannot be added at all until the core is done.
side chain is added in repeating units of 3-5 NEVER AS SINGLE SUGARS

Question 23

how are core sugars added vs antigenic sugars?

Answer 23

core - one at a time

antigenic - in 3-5 subunits

Question 24

Explain Brauns Lipoprotein

Answer 24

• one of the most abundant proteins in the cell
• connects OM to PG
• Has a N-terminus which is cysteine group on OM
• Has a C-terminus which connects a lysine group to the DAP part of PG

Question 25

Explain Outer Membrane proteins? what is the common one? what are their properties?

Answer 25

• usually rare, bacteria only have a few
• usually acidic
• usually form a trimer and act as a porin to allow hydrophilic substates past the OM
• non covalently associated with PG
• On the surface of cell and often act as bacteriophage receptors too

Question 26

T or f, Gram negative and positive cells have OMP’s

Answer 26

NO, how can positive have them without an OM??

Question 27

What is the one OMP that has a structural role?

Answer 27

OMP-A

Question 28

what are the OMP’s that are non specific porins?

Answer 28

OMP-F and OMP-C

Question 29

What do PhoE, LamB, Tsx, and TonA allow in?

Answer 29

PhoE - phosphate
LamB - lamba recpetor, Maltose
Tsx - T6 receptor, lets in nucleosides
TonA - T1 receptor, lets in ferrichrome

Question 30

True or false, the periplasm is a large

Answer 30

false, it appears large in microscope but its not. Its small due to pressure and Brauns lipoprotein