Bacterial Structure & Function

Question 1

Characteristics of G+ or G- cell wall

Answer 1

G+: very thick PG layer, +/- capsule

G-: thin PG layer between inner and outer membrane, +/- capsule

Question 2

Gram positive envelope components

Answer 2

No true periplasmic space; IM, OM, and TM proteins; have teichoic and lipoteichoic acid

Question 3

Significance of teichoic and lipoteichoic acid

Answer 3

Specific for G+
TA: cross-links PGs, not embedded in membrane
LA: cross-links PGs, also embedded in outer membrane; a pyrogen (not as bad as LPS)

Question 4

Gram negative envelope components

Answer 4

True periplasm between membranes with thin PG layer
OM: unique to G-
LPS on OM: lipid A (strong pyrogen), O-antigen (polysach)
K-antigen: specific to G-

Question 5

G-: smooth vs. rough appearance on agar plate

Answer 5

Smooth: long PS surface molecules
Rough: lipid A and short PS -> matte on plate

Question 6

Significance of O-antigen

Answer 6

Immunogenic because on outside, strains can be serotyped, specific strains important in different conditions

Question 7

Key features of O-antigen

Answer 7

Lipid A: an endotoxin with many FA chains, highly conserved, G- specific
Core PS: highly conserved, contains KDO acid (G- specific)
O side chain: types strain, very non-conserved

Question 8

Peptidoglycan synthesis

Answer 8

MurA-F makes UDP-MurNAc
MurY transfers it to undecaprenyl-P = lipid 1
MuG adds GlcNAc (from UDP-GlcNAc) = lipid 2
Translocated by flippase to periplasm, where PGTs & TPs elongate PG chain

Question 9

Energy for transpeptidation

Answer 9

Second D-Ala (of D-ala, D-ala) reacts with free AA = energy (no ATP used), lose D-ala
Same for G- & G+, but G+ adds AA in between linkages

Question 10

Gram stain method & outcome

Answer 10

Fixation to slide, crystal violet, iodine (helps CV hold on), decolorization, counter stain safranin
*Blue stain remains in G+ bc think PG layer, but released from G-

Question 11

Differences in H antigen between G+ & G-

Answer 11

H antigen = flagellin
G+: shorter TM portion
G-: longer TM portion (to span both membranes)

Question 12

Bacterial growth phases

Answer 12

Lag phase
Log phase (exponential growth in optimized conditions)
Stationary phase (nutrients exhausted or waste products build up)
Death (decline) phase (never reaches zero)

Question 13

Bacterial replication in G- bacteria

Answer 13

After chromosome replication & polarization, Z-ring forms into noose and pinches off/degrades PG, which is resynthesizes after separation

Question 14

Bacterial replication in G+ bacteria

Answer 14

After chromosome replication & polarization, Z-ring forms into a noose, GP septum forms and remodels into 2 cells

Question 15

Endospore formation

Answer 15

In some G+
Chromosome replication & septum formation in forespore
Engulfment of forespore by cell
Cortex (PG) and keratin-like coat synthesized
Maturation (replace water with DPA or Ca2+ dipicolinate)
Mother cell lysis

Question 16

DAP vs. DPA

Answer 16

DAP: diaminopimelic acid, 3rd AA in E. coli PG synthesis
DPA: dipicolinic acid, can replace water in endospore maturation

Question 17

Virulence factors

Answer 17

Adherence, persistence, invasion, toxigenicity

Question 18

Bacterial adherence

Answer 18

Pills with adhesin to recognize host protein

Afimbrial adhesion: adhesin on organism itself, no pilli

Question 19

Bacterial persistence

Answer 19

Attachment to surface, production of EPS (exo-PS) = irreversible attachment, dev & maturation of biofilm, dispersion of single cells from biofilm

Question 20

Bacterial invasion

Answer 20

Paracellular, translocate through M cell, trans-epithelial migration, luminal capture by dendritic cells, growth inside MF, entry through epithelial cells, hijack actin to rocket from cell to cell

Question 21

Bacterial toxins

Answer 21

Released exotoxin can cause pore formation, cleave surface molecules, bind receptor to enter cell or cause activation of target, modulate activation
Hypodermic: a pillus-like structure inserts into cell

Question 22

Thanatomicrobiome

Answer 22

Post-mortem microbiome that may help find COD, TOD