Week 1 Cell Structure I

Question 1

Microbial Systematics as Chronometer

Answer 1

1. Present in all organisms
2. Well conserved
3. Mutation at constant rate (SSU rRNA)

Question 2

Ribotyping Bacteria and Archaea

Answer 2

1. Agar plate with isolated colonies + natural microbial community
2. DNA and eventually rRNA created for PCR
3. Sequencing and phylogenetic tree construction

Question 3

Gram Positive

Answer 3

1. Thick peptidoglycan with cytoplasmic membrane

2. Teichoic acids (- charge; cell wall): structural support and ion transport via cationic attraction to cell surface

Question 4

Gram Negative

Answer 4

1. Thin peptidoglycan with cytoplasmic membrane, periplasm and outer membrane
2. LPS: O-specific and core polysaccharides for immunity against infection; defines serotypes; Lipid A (endotoxins for pathogens)
3. Porins
4. Periplasm: sensory zone (environmental, binding proteins, degrading enzymes, and solute metabolites)

Question 5

Gram Stain

Answer 5

1. All purple –> dye binding peptidoglycan
2. All purple + iodine –> mordant with dye
3. Gram + is purple, Gram - is colorless; + alcohol for decolorization –> dissolve lipids and solvates dye
4. Gram + is purple, gram - is red (counterstain destined gram - cells with safranin)

Question 6

Peptidoglycan

Answer 6

Polysac with N-acetylglucosamine (NAG with acetate, esp in arthropod exoskeletons) and N-acetylmuramic acid (NAM with ether/lactic acid; along with diaminopimelic acid DAP in bacteria only)
> NAM+LA = oligopeptide crosslinking reactivity
> NAG + NAM + AA –> rigid glycan tetrapeptide repeats

Question 7

Antibiotics

Answer 7

1. Bacitracin + Vancomycin: block G+ peptidoglycan
2. Cephalosporins + Penicillin (b-lactams): block transpeptidase crosslinkers
3. Lysozymes: break down G- peptidoglycan

Question 8

S-Layer (Outermost outer layer; ONLY cell wall structure in many Archaea)

Answer 8

1. Heavily glycosylated surface protein lattices

2. Protection, cell adhesion, surface recognition, ion traps, scaffolding for enzymes/virulent factors

Question 9

Mycobacteria (Acid-fast Bacteria)

Answer 9

1. TB and Leprosy/Hansen’s disease
2. Antimicrobial-resistant: thickest cell walls with waxy mycolic acids (60-90C)
3. Neither G+ nor G-

Question 10

Microbials w/o Cell Wall (HIGHLY EVOLVED)

Answer 10

1. Mycoplasmas (bac): pathogenic/parasitic
   > Sterols strengthen cytosplasmic membrane
   > Ab resistant (no cell wall synthesis as target)
2. Thermoplasmatales (arc):
   > Acidophiles: membranes form tetraether monolayer
   > Lipoglycans anchor lipids