Gram Negative Cell Surface

Question 1

What are the key features of the Periplasm

Answer 1

1. Inbetween outer and inner membrane
2. densly packed with proteins and more viscous then cytoplasm.
3. cellular compartmentalization which allows RNase and Phosphatase activity for degradation
4. has periplasm binding proteins for sugar/amino acid transport and chemotaxis
5. chaperone like molecules

Question 2

The outer membrane contains?

Answer 2

1. Asymetrical due to its contents composition
2. Lipopolysaccharide
3. surface layers (s-layers)
4. phospholipids
5. porins

Question 3

What are porins and what are the used for?

Answer 3

Channels in the outer membrane that are often arranged as trimers that allow access to hydophillic nutrients but also molecules lower than 5000Da in size.

Question 4

What does a lipopolysaccharide consist of?

Answer 4

O-specific polysaccharide or O-antigen which is highly conserved
Polysaccharide which is variable between species (core region)
Lipid A which is conserved

Question 5

What is Lipid A and what is its function

Answer 5

• Consists of glucosamine, phosphates and membrane anchors (found attached to phospholipids in outer membrane)
• Is an Endotoxin and is recognised by Pathogen associated molecular patterns (pamps) by immune systems.
• Causes Inflamation by TLE-4
  Can cause endotoxic shock

Question 6

Core polysaccharide consists of

Answer 6

KDO, Hexose and sugars.

Question 7

O-specific polysachharide consists of

Answer 7

Sugars with large variability and is a repeating unit.

Question 8

Pattern recognition molecules are?

Answer 8

Molecules that recognise PAMPS which are soluble and complementary. The membrane bound family are TLRs.

Question 9

What is the O-antigen and why is is important

Answer 9

Structurally variable with more then 60 monosaccharides and more then 30 non-carbohydrates modification.

• its linear
• exists as homopolymers or heteropolymers and all vary in length
• can be used to recognise virulence
• used to evade immune system and vaccines can be developed.

Question 10

What are the functions of Gram negative envelop

Answer 10

• Molecular sieving barrier
• Exclusion limit of oligosaccharides of 650-900da
• s layers all sieve of 20000 - 45000da

These make it a efficient permeable membrane

Question 11

Greatly a from gram stainings

Answer 11

Positive = purple appearance 
Negative = pink 

It’s purple in positive as crystal violet cannot diffuse out as of thick peptidoglycan as pores close as its dehydrated.

Question 12

What are the steps to gram staining

Answer 12

1 heat fix

2 crystal violet (both types purple)

3 grams iodine

4 decolorize (gram negative clear)

Counter stain (gram pos purple and negative pink)

Question 13

What are surface layers

Answer 13

Glycoproteins
They self assemble into crystalline arrays
Form pores 2-8nm
Found in arches is common
Outer most layer of cell and primitive semi permeable.

Question 14

How many types are there of s layers

Answer 14

3 types

1,4 and 6 identical subunits

Question 15

What is the function of s layers

Answer 15

• Thermal, mechanical and osmotic stability
• Protection against particles, immune system and predators
• Interaction with the environment, protein immobilisation, phage receptor, adhesion to surfaces and pathogenic virulence factor.