Gram Negative Bacteria-Mycobacteria and cytoplasmic membrane

Did the original gram stain have a counter stain?

No it did not

What is a common feature in peptidoglycan between gram positive and gram negative bacteria?

1. Both have NAG and NAM

2. End in D-ala

What is the structure of beta lactam drugs?

They have a beta lactam ring and D-ala, D-ala

What is the mechanism of action for beta lactam drugs? Why can they do this?

The beta lactam drug will bind to the penicillin binding protein instead of the dipeptide required for the synthesis of peptidoglycan. This is because they are structural analogs of the dipeptide.

What type of inhibition is taking place at the penicillin binding protein?

Competitive inhibition

What are cell wall hydrolases essential for? What are they commonly referred to as?

Cell division, separation, cell wall morphogenesis, and turnover. Autolysins

Why are hydrolases required for cell division and separation?

This is because certain segments of the cell wall require cleavage in order to facilitate cell division

What condition must occur for cell wall hydrolases to work?

They must be highly regulated

What does disturbance to hydrolases result in?

Autolysis/cell death

What are 3 types of cell wall hydrolases?

1. N-acetylglucosaminidase

2. N-acetylmuramidase

3. Endopeptidases

Describe the cell wall turnover pathway

1. Peptidoglycan is recycled by autolysins into NAM-tripeptide (break peptide and glycosidic bonds)

2. AmpD will catabolize NAM-tripeptide and recycle it into new peptidoglycan

What is another role of NAM-tripeptide

It is a positive activator for AmpR

Describe what happens when there is lots of peptidoglycan being recycled

1. Too much peptidoglycan is being broken down for the recycling pathway

2. NAM-tripeptide will spill down and activate AmpR

3. AmpR will increase transcription of ampC

4. ampC will activate B-lactamase

Is the mycobacterial cell wall waxy? Hydrophobic or hydrophilic? High or low lipid content?

Waxy, hydrophobic, and high lipid content

What percentage of the dry weight of mycobacterial cell wall is mycolic acids?

60%

What are mycolic acids?

Long chain and branched fatty acids

What is the peptidoglycan layer linked to in mycobacterial cell walls?

Arabian-galactan (D-arabinose and D-galactose) which is then linked to high MW mycolic acids

What is laid on top of the arabino-galactan/mycolic layer?

Layer of proteins

What are two additional glycolipids in mycobacterial cell walls?

1. Lipoarabinomannan

2. Phosphatidylinositol mannosides (PIM)

Are mycobacteria acid fast?

Yes they are

What is able to transport small hydrophilic molecules through the outer layer of mycobacteria?

Porins

Do mycobacteria have thinner or thicker peptidoglycan?

Have thinner peptidoglycan than gram positive (slightly thicker than gram -)

Why are mycobacteria acid fast? What does this mean?

Due to mycolic acids. It is hard to get a stain into the bacteria but once you do it is very difficult to remove it

Does mycobacterium tuberculosis remain dormant in individuals (latency TB)? Is it hard to treat?

Yes it usually does and only a small percentage of people develop primary TB. Yes it is hard to treat

What is the difference between gram +, -, and mycobacterial cell envelopes in terms of composition?

Gram +: Peptidoglycan, TA, LTA

Gram -: Peptidoglycan, LPS, lipoprotein

Mycobacteria: Peptidoglycan, mycolic acids

What is the difference between gram +, -, and mycobacterial cell envelopes in terms of thickness?

Gram +: Thick (20-80nm)

Gram -: Thinner (8-11nm)

Mycobacteria: Thick (20-60nm)

What is the difference between gram +, -, and mycobacterial cell envelopes in terms of outer membrane?

Gram +: No

Gram -: Yes

Mycobacteria: No

What is the difference between gram +, -, and mycobacterial cell envelopes in terms of periplasmic space?

Gram +: No

Gram -: Extensive

Mycobacteria: Narrow/absent

What is the difference between gram +, -, and mycobacterial cell envelopes in terms of porins?

Gram +: No

Gram -: Yes

Mycobacteria: Yes

Describe the structural composition of the bacterial cytoplasmic membrane

1. Phospholipid bilayer

2. Proteins (integral and peripheral)

What is half the membrane composed of? What do they act as?

Proteins. Act as recognition proteins, enzymes, receptors, carriers, or channels

What is the current model used to understand the membrane?

Fluid mosaic model

Do integral or peripheral proteins require more harsh methods to separate them?

Integral

Describe the chemical composition of phospholipids

Have 2 fatty acids chains attached to the 2 carbon atoms of glycerol by ester bonds

What carbon is the phosphate group attached to on the glycerol of a phospholipid?

Third carbon

Is phosphate always bonded to the third carbon on glycerol?

No, different molecules can be which gives rise to different types of phospholipids

Are phospholipids hydrophilic or hydrophobic?

Amphipathic (fatty acids are hydrophobic and polar head is hydrophilic)

What happens when phospholipids are placed in a watery environment?

They form micelles