CH 3c outer structures and gram staining

Question 1

CH 3c

Outer membrane

Answer 1

Gram negative bacteria only
Porin protein channel - transport of small molecules
Specialized receptors - transport of large molecules
Considered to be part of the wall, it’s very toxic

Question 2

CH 3c

Cell wall

Answer 2

Outside of plasma membrane (in G-neg bacteria, it’s between the two membranes)
Functions:
- cell structure and shape
- prevents osmotic lysis
- protection against toxic substances
- contributes to pathogenesis
Mycoplasma lacks typical cell wall (pleomorphic)

Question 3

CH 3c

Cell wall: Gram-negative v. Gram-positive

Answer 3

G-positive: thick layer of peptidoglycan

Gram-negative: thin layer of peptidoglycan; outer membrane

Question 4

CH 3c

Peptidoglycan

Answer 4

Backbone: basic chain of alternating sugars (NAM and NAG)
Short peptide chain of four D and L alternating amino acids off of the NAM sugar
Backbone forms a helix with cross links between the peptide chains - forms 3D structure of cell walls. (peptide bonds between 4th amino acids)
Gram-negative links directly between amino acids, making a tighter scaffold and denser cell wall.
Gram-positive links using a glycine bridge, making for a looser scaffold.

Question 5

CH 3c

Gram-positive cell walls

Answer 5

Could have up to 17 layers of peptidoglycan.
No outer membrane.
Unique acids:
- teichoic acids (peptidoglycan layer)
- lipoteichoic acids (membrane)

Question 6

CH 3c

Teichoic acids

Answer 6

Can be formed using glycerol or ribitol sugars. joined by phosphate groups
Not really sure about the function… maybe for protection from other cells or used as an anchor to a flat surface?

gives cell wall negative charge

Question 7

CH 3c

Gram-negative cell walls

Answer 7

Smaller peptidoglycan layer, outer membrane

• space between inner membrane and outer membrane is called the periplasmic space (like a screen porch) - it’s a functional space that extends the usable surface area of the cell
  *

Question 8

CH 3c

Periplasmic space

Answer 8

space between plasma membrane and outer membrane for gram negative and pm and cell in in gram positive bacteria. can have proteins, help with nutrient transport, metabolic funcitons

Question 9

CH 3c

Gram-negative behavior b/c of the outer membrane

Answer 9

G-neg cells’ outer membrane has many different macromolecules that have a variety of functions and cause Gram-negative bacteria to have different behaviors/ characteristics.

Question 10

CH 3c

Outer membrane macromolecules

Answer 10

Lipopolysaccharides
Porin transport proteins–aidin permeability
Braun’s lipoproteins–attaches outer membrane to cell wall

Question 11

CH 3c

Lipopolysaccharides (LPS)

Answer 11

Make up the outside layer of the outer membrane's bilayer. Lipids attached to complex sugar molecules.
Three components:
O antigen
Core region
Lipid A

Question 12

CH 3c

Lipopolysaccharides - O antingen

Answer 12

Very unique - variation even within species, unique to the strain of that species
Hydrophilic
What human antibodies recognize and target (hence name “antigen) - some species adapt very quickly, however, and can change their O antigens faster than our immune systems can register and fight them.
Also help regulate what enters the cell - bent chains form a kind of shield that prevents unwanted chemicals from entering.

Question 13

CH 3c

Lipopolysaccharides - core region

Answer 13

Composed of sugars - not much variation between species

Question 14

CH 3c

Lipopolysaccharides - Lipid A

Answer 14

Hydrophobic
Phosphorylated sugar head group with multiple fatty acid tails
Responsible for toxic effects of LPS - cause inflammatory response; funnily, as long as the bacteria is alive and its outer membrane is intact, we’re not exposed to the Lipid A, but when they die and break apart is when we’re exposed to the Lipid A toxin.

Question 15

CH 3c

Porin proteins

Answer 15

Transport proteins that are very specialized.

Question 16

CH 3c

Braun’s lipoproteins

Answer 16

Anchors outer membrane to the cell wall.

Question 17

CH 3c

Cell Wall of bacteria as a Target

Answer 17

Bacterial cell walls act as protection from lysis due to osmotic pressure - there are many natural and manufactured defenses that target the cell wall in order to kill the bacteria.
Lysozyme
Penicillin
Both are more effective against Gram-positive bacteria than Gram-negative because the G-pos cell wall is exposed while the G-neg cell wall is protected by the outer membrane.

Question 18

CH 3c

Lysozyme

Answer 18

Natural defense mechanism that kills bacteria by breaking apart the glycosidic linkages between NAM and NAG (backbone of cell wall).
Found in human tears and saliva (entry points to the body) - also found in chicken eggs.

Question 19

CH 3c

Penicillin

Answer 19

Inhibits formation of crosslinks between peptide chains in cell wall.

Question 20

CH 3c

Gram stain procedure

Answer 20

It’s a differential stain - divides bacteria into groups based on their reaction to the stain. Is it G-pos or neg? Pos = purple; Neg = pink

1. Stain all cells with Crystal Violet
2. Iodine treatment - I binds to CV, forming large molecules
3. Decolorization - use alcohol to remove stain
4. Counter stain with Safranin (pink dye). Gram-negative are pink while Gram-positive are still purple from the Crystal Violet stain.

Question 21

CH 3c

Why is the decolorization step in the Gram staining procedure so important?

Answer 21

allow you to ID bacteria as either G-neg or G-pos. Because G-neg bacteria have a much thinner cell wall, the large complex formed by the Crystal Violet stain and the iodine will be able to leave the cell, making the bacteria clear (it will show up as pink after the additional staining in the fourth step).
The cell walls of G-pos bacteria are much thicker, so the large CV-I complex can’t get out of the cell, leaving it purple even after the additional staining in step four.

Question 22

CH 3c

Glycocalyx

Answer 22

Also known as a capsule or slime layer.
Very thick, dense, and organized.
Generally composed of polysaccharides.

attachment

Question 23

CH 3c

Capsule

Answer 23

Function:

• resist phagocytosis
• resist desiccation
• exclude bacteriophages (viruses that attack bacteria)
• adherence*** (allow them to stick to mucous membranes and cause illness rather than being washed away, and avoid phagocytosis bc macrophage can’t get around it) Make pathogenic bacteria more pathogenic - it’s a virulence factor

Question 24

CH 3c

Capsules/ slime layers as a virulence factor

Answer 24

Adherence of bacteria to surfaces (rather than being washed away) makes pathogenic bacteria more pathogenic. w00t…

Question 25

CH 3c

Slime layer

Answer 25

More diffuse than a capsule
Easily removed
Same functions as capsule + gliding motility

Question 26

CH 3c

S layers

Answer 26

Structured layer of protein or glycoprotein - protective layer outside of bacteria
Autocatalytic formation
Maintains cell shape/ rigidity
Aids in attachment to surface
Protection

• ion and pH fluctuation
• osmotic stress
• enzyme activity (protects against)
• predatory bacteria

Question 27

CH 3c

Autocatalytic formation

Answer 27

proteins only need to be present and they form correct structure on their own - interesting properties for research