Midterm 1.3

Question 1

Which bacteria (gram +/-) has interbridges? Explain its function (!)

Answer 1

Gram +
Helps connect different peptidoglycan layers. These are also peptide crosslinks, extended by a few amino acids
(This way provides additional strength)

Question 2

Which bacteria (gram +/-) has teichoic acids? Explain its function (!)

Answer 2

Gram +
Provide cell strength
Help trap divalent metal ions such as Mg2+
Barrier & attachment functions

Long polymers comprised of glycerol phosphate or ribitol phosphate with attached D-glucose and/or D-alanine

Covalently attached to peptidoglycan or cytoplasmic membranes

Question 3

Explain gram staining for gram + bacteria

Answer 3

Gram + thick layer of peptidoglycan is dehydrated - pores close and prevent escape of crystal violet dye - cells are stained purple

Question 4

Explain gram staining for gram - bacteria

Answer 4

Decolorizing agent degrades outer membrane, thin/porous peptidoglycan layer does not retain purple stain. Cells appear pink due to safranin counterstain

Question 5

Mycoplasma

Answer 5

Unusual bacteria that lacks cell walls
- An intracellular parasite that lives within host cell
- Minimal osmotic pressure within host cell - cells burst in low solute environments
- Specialized/unusually strong cell membrane

Question 6

Lysosome

Answer 6

Enzyme that degrades peptidoglycan

Question 7

Protoplasts/spheroplasts

Answer 7

A bacterial or plant cell with the cell wall removed

Question 8

What is the outer membrane/leaflet of gram - bacteria composed of?

Answer 8

An important molecule called LPS (lipopolysaccharide)

Question 9

What are the 3 parts of LPS?

Answer 9

1. Lipid A (within membrane)
2. Core polysaccharide
3. O-specific polysaccharide (outermost component)

Question 10

Explain the features of the lipid A

Answer 10

Hydrophobic tails anchor Lipid A in OM - base of LPS
Phosphates confer a negative charge

Question 11

What can endotoxin lead to?

Answer 11

Can lead to a potent and unchecked immune response - can cause septic shock if detected in bloodstream

Question 12

Why can lipid A be sensed as an endotoxin?

Answer 12

Lipid A is not made by humans ever, which means that if this lipid is detected in the bloodstream it means we have a bad bacteria in the bloodstream

Question 13

O-specific polysaccharide

Answer 13

polysaccharide
Polysaccharide comprised of diverse sugar subunits connected and branched in different ways
Also called O antigen

Question 14

What is the current view of outer leaflet of the outer membrane in respect to LPS and phospholipid? (!)

Answer 14

The outer leaflet of the outer membrane is mostly (or almost exclusively) LPS with very little phospholipid

Question 15

What is inner leaflet of outer membrane composed of? How does that affect outer membrane?

Answer 15

The inner leaflet is comprised of phospholipid. Therefore it is asymmetrical

Question 16

What is the function of Braun’s lipoprotein? (!)

Answer 16

Serves to connect the outer membrane to cell wall

Question 17

Porins (!)

Answer 17

Protein channels that serve as channels for entrance/exit of small molecules
- Can be specific or non-specific
(Can remember as pores)

Question 18

What are the major functions of the outer membrane?

Answer 18

1) Provides mechanical strength to the cell - ionic bonds between adjacent LPS molecules via divalent metal ions
2) Important barrier. Soaks up or blocks access to many molecules - important for antibiotic sensitivity
3) Protects cell wall
4) Enables a substantial periplasmic space

Question 19

Periplasmic space (“periplasm”)

Answer 19

Space between cytoplasmic/outer membranes of gram - bacteria
Much smaller space between cell membrane and cell wall in gram + bacteria

Buffer between environment and cell
- Break down macromolecules for uptake as nutrients
- High affinity binding protein for nutrients
- Detoxify harmful compounds
- Protein folding - disulfide bond formation

Question 20

S-layer

Answer 20

Rigid/permeable monolayer of protein or glycoprotein - self-organized into a repeating structure that encompasses the cell
Always the outermost layer of the cell
Often a protective layer
Can provide a periplasmic space or keep external proteins from accessing OM or cell wall

Question 21

What is the similarity and difference between capsules and slime layers? (!)

Answer 21

Similarity: both are coats of polysaccharides around the cell surface
Have same function
Adhering to the surfaces, protection from host immune cells (bacterial pathogens) & protection from water loss/dehydration
Difference: Capsules are organized into a matrix and attached to the cell while slime layers are loosely attached, less organized

Question 22

Group translocation

Answer 22

Transporter substance is bound by a transporter and is chemically modified during transport
- Phosphotransferase system (!). Glucose uptake and also transports other sugars.
- Membrane is impermeable to the phosphorylated sugar molecule - remains in cell
- Hydrolysis of PEP

Question 23

ABC transporters

Answer 23

ATP binding cassette use ATP to power the transport of substances across the cytoplasmic membrane
- 2 ATPase domains (proteins) provide energy
- Transmembrane domain(s) (proteins) provides selective channel
- Substrate binding protein binds molecule with high affinity and delivers it to the channelc