micrb lec 3
What are the main layers/components of a bacterial cell envelope shown in the slide?
Plasma (inner) membrane, peptidoglycan, periplasm, and (in Gram−) an outer membrane; cytoplasm is inside.
What is the periplasm and why does it matter?
The space between inner membrane and outer membrane (Gram−) that contains proteins/enzymes and where some exported proteins first arrive before going outside.
What do Type I and Type II secretion systems have in common?
They span both inner + outer membranes and secrete proteins.
What is special about Type II secretion?
It exports proteins that first get into the periplasm via Sec or Tat, then Type II ships them out of the cell.
How is Type V secretion described in the slides?
Similar “final step” idea as Type II, but only found in the outer membrane.
What does Type III secretion do?
Secretes proteins into a host cell (host-directed).
What does Type IV secretion transport (and why is that important)?
DNA; linked to reproduction/horizontal gene transfer.
What is the “needle-like” secretion system and how does it work?
Type VI: starts retracted, then fires/extends through a target membrane to deliver protein (often toxin).
What are S-layers?
A crystalline layer of (glyco)proteins that forms 2D sheets attached to LPS or peptidoglycan.
Are S-layers common in bacteria? Where are they more common?
Uncommon in bacteria, more common in archaea.
What do S-layers protect against?
Bacteriophage, low pH, and lytic enzymes.
What is a capsule/glycocalyx
Really long polysaccharides around the cell that provide protection
What kinds of protection do capsules provide?
Protection from immune systems and desiccation (drying out).
List the glycocalyx/capsule-related components named in the slide
LPS/teichoic acid/S-layer glycans, capsule, alginate, poly-N-acetylglucosamine, enterobacterial common antigen, cellulose.
What are pili (basic definition + size + composition)?
Thin filamentous protein structures, ~2–10 nm diameter, extending from the cell surface.
Where are pili found (Gram status)?
In all Gram-negative and many Gram-positive bacteria.
What does “retractable” pili mean functionally?
They can extend and retract, enabling pulling/twitching movement and attachment-based behaviors.
What are the key pili “types/roles” listed?
Fimbriae, conjugation pili, electrically conductive pili, Type IV pili.
What is the big idea of Type IVa pilus structure (why it’s built that way)?
The structure supports stability/ability to pull (traction).
How is a Type IVa pilus extended according to the slide?
It’s pushed/extended from the bottom (assembly machinery drives it outward
What is twitching motility?
Fast, jerky movement: pilus extends, adhesive cap attaches to surface, then pilus retracts and pulls the bacterium.
What is gliding motility (how described)?
Less understood; involves proteins anchored to the surface forming a helix and threading Mre proteins to move along a surface.
What is swarming and what mediates it?
Coordinated movement on semi-solid surfaces, mediated by flagella, producing dendritic patterns; needs low-concentration agar.
What is “swimming motility” and what structure enables it?
Movement in liquid; flagella spin like a propeller to push bacteria forward.
Name the flagellar arrangements shown.
Peritrichous, polar, lophotrichous.
What are the two “major components” of a flagellum described?
Stator (stationary, anchors in inner membrane + peptidoglycan) and rotor (spins).
What is the basal body?
The part of the flagellum located in the inner membrane (the motor/anchor region).
How does a flagellum grow/assemble?
It’s hollow; new flagellin travels through the center and is added at the end/tip
What energy source powers bacterial flagellar rotation
Proton motive force: higher H⁺ in periplasm than cytoplasm; protons flow down gradient.
What happens in peritrichous bacteria during a “run” vs “tumble”?
run: flagella bundle → forward motion. Tumble: rotation change spreads them apart → reorientation
What’s different about “reversible flagella”
In some polar systems, clockwise rotation can cause reversal/backing up rather than tumbling.
Define chemotaxis.
Movement of bacteria in a chemical gradient.
What’s the key behavior pattern in chemotaxis toward attractants?
Cells run longer while chemical concentration increases; they tumble more when concentration decreases → net movement toward attractant.
What happens if there is no chemical gradient?
Motility can still occur but it’s not directional (more random, lots of tumbling).
Name 3 other “taxis” types and what they respond to.
Light taxis (wavelengths of light), aerotaxis (oxygen concentration), magnetotaxis (magnetic field).
What is the slide “Archaea vs bacteria” mainly signaling?
That differences can show up in genome, ribosomes, inclusions, plasma membrane, cell wall, and motility structures.
What archaeal shapes/arrangements are shown?
Broad/oval, clusters, branched, and thin square forms.
What is the key chemical difference in archaeal membrane linkages?
Archaeal lipids use ether linkages, not ester.
What are archaeal lipid tails based on (vs fatty acids)?
Phytanyl chains based on isoprene units (not fatty acids).
What membrane structures can archaea have, and which is more stable?
They can have a bilayer or a monolayer; monolayers are more stable and common in thermophiles.
What is crenarchaeol (as described) and what does it affect?
A lipid with ring-like structures that helps change membrane fluidity in archaea.
What are the archaeal cell wall/envelope options
Pseudomurein, methanochondroitin, S-layers, and a proteinaceous sheath.
What is pseudomurein (how it’s framed vs peptidoglycan)?
A peptidoglycan-like structure with a glycan backbone + peptide interbridges (but chemically different).
Why can’t lysozyme cleave pseudomurein like peptidoglycan?
The linkage is different from the β(1→4) bond lysozyme targets in peptidoglycan.
What is methanochondroitin’s function
An external polymer aiding desiccation resistance, stability, and protection.
What is an archaeallum and how is it powered?
An archaeal motility structure similar to a flagellum, but uses ATP (not proton motive force).
Where is archaeallum anchored and why?
Anchored in the S-layer to provide stability.
What are archaeal hami and what do they do?
Pili-like structures with a 3-prong hook used like a grappling hook for attachment/pulling.
What are the 4 phases of the bacterial growth curve
Lag, exponential (log), stationary, death.
What happens in the lag phase?
Cells internalize nutrients, make enzymes, replicate cellular components—metabolically active but not increasing in cell # yet.
What defines the exponential phase?
Population doubles as fast as possible; growth is linear on a log scale; rate depends on organism + conditions.
What is generation (doubling) time?
Time for a population to double; varies by species and environment.
What is the generation time range given?
From ~10 minutes (some bacteria) to several days (some eukaryotic microorganisms).
What happens in the stationary phase?
Nutrients run out; growth slows; some die; no net increase; can include endospore synthesis.
What happens in the death phase (as described)?
Plasma membrane ruptures and DNA is destroyed.
How does growth “outside the lab” usually differ?
Slower than optimal, not linear progression, often mixed culture, often in biofilms; nutrients limiting.
What is a biofilm
A cluster of bacteria producing a polysaccharide matrix that protects them from the environment.
Define asexual vs sexual reproduction
asexual: one chromosome set → genetic clones. Sexual: combining genetic material from two organisms → new organism.
List the asexual reproduction methods named.
Binary fission, budding, fragmentation.
What “pseudosexual” processes are listed for microbes?
Conjugation, transformation, transduction.
Summarize binary fission steps
Cell elongates as components replicate → septum (peptidoglycan barrier) forms → septum pinches → two cells.
What’s the key DNA replication/segregation logic described (E. coli)?
Circular chromosome with oriC bound by DnaA recruits polymerase; then SeqA blocks oriC as elongation occurs; chromosomes segregate; Z-ring forms; division.
What does FtsZ do during cytokinesis?
Selects the center site, assembles the Z ring, links it to membrane, recruits cell wall machinery, constricts to form septum.
What are the main facts about the E. coli divisome on the slide?
~10,000 FtsZ polymerize into central ring; tethered by ZipA + FtsA; localizes peptidoglycan biosynthesis.
What nucleotides/energy are mentioned for Z-ring/divisome formation?
Z-ring requires GTP; recruitment is energy-dependent and mentions ATP hydrolysis.
How does the cell “know” the center for Z-ring placement (Min system)?
MinC/MinD prevent FtsZ ring formation; MinE accumulates at center, removing MinCD activity there so Z-ring can form.
What timing fact is given for E. coli division
About ~1.5 hours from 1 cell to 2
Where does new peptidoglycan get synthesized during division?
In the middle at the forming septum, anchored by the FtsZ ring.
What are the big steps of peptidoglycan biosynthesis listed?
Build blocks → build disaccharide-peptide repeat → translocate to periplasm → transglycosylation → transpeptidation.
What does “transglycosylation” do in peptidoglycan building?
Forms glycan linkages (polymerizes the sugar backbone).
What does “transpeptidation” do?
Forms peptide crosslinks (peptide bonds) between strands.
Where are precursors made (location)?
On the cytoplasmic face of the plasma membrane.
What is UDP-GlcNAc’s role
It comes from glycolysis, provides one backbone component, and serves as a donor sugar; the other backbone component is NAM.
What carrier moves peptidoglycan subunits across the membrane?
Undecaprenyl phosphate carrier (slide spells similar: “undecopranal phosphate”).
What happens after translocation according to the slide?
The repeat unit reaches the outside/periplasmic face, then polymerization/crosslinking steps proceed.
(F6P → final steps).
F6P → UDP-NAG → UDP-NAM → UDP-NAM-pentapeptide → lipid-linked intermediates (BP-PO4 forms) → add UDP-NAG → translocation → transglycosylation → transpeptidation.
What is “unequal division”
Requires stalk adherence to a surface; forms a daughter cell that is flagellated and swims away.
What is “polar growth without differentiation of cell size” (as listed)?
A growth/division mode where growth occurs at a pole but without producing different-sized cells (listed as a category).
S-layers can be found in: bacteria, archaea, both, or neither?
Both — less common in bacteria, common in archaea.
If a bacterium loses its S-layer (mutant) vs wildtype, what changes in pH tolerance?
Wildtype tolerates harsher (lower) pH better; S-layers help protect against low pH/lytic conditions.
Antibiotic targets sugar alcohol biosynthesis in cell envelopes — which bacteria are most affected and why?
Gram-positive, because sugar alcohols are a key part of teichoic acids, which are attached to peptidoglycan.
Twitching motility is mediated by the type IV pilus, which is based on a type II secretion system.” Correct?
yes
If PMF is destroyed, what immediately stops (key rule)?
Bacterial flagella-based motility stops (PMF powers flagellar rotation).
PMF is to flagella as ____ is to archaeallum.
ATP
During chemotaxis (vs no gradient), what changes about run/tumble behavior?
Cells still tumble, but they have longer runs toward the attractant (nutrient).
Which is true of peptidoglycan but not pseudomurein?
Sensitive to lysozyme (pseudomurein resists lysozyme because its linkage differs).
Put Haloquadra walsbyi in a hypertonic solution — what happens (best immediate answer)?
It shrinks as water leaves the cell.
(Adaptation concept: halophiles counter later by increasing compatible solutes like glycine betaine, not decreasing.)
Most abundant lipid in a hyperthermophilic bacterium membrane (best choice)?
Saturated phospholipids (stiffer/less fluid at high temp).
Growth curve: dotted line rises more slowly but reaches a similar plateau — what explains it?
Slower doubling time.
If halfway through stationary phase you add an antibiotic that stops growth but doesn’t kill, what does the curve do?
It stays flat (no further increase and no death-phase drop).
Start with 2 cells in exponential phase. After 3 generations, how many cells?
2 x 2^3= 16
“In E. coli, genome replication takes ~20–30 min in rich conditions during exponential phase.” True/false?
true
Best protein that ensures septum forms in the middle (best answer)?
MinE (it clears MinCD from midcell so FtsZ can form the Z-ring there).
In E. coli peptidoglycan, how many amino acids are in the cross-linked stem peptide after crosslinking?
4 — the terminal D-Ala is removed during transpeptidation, leaving a tetrapeptide.
Which image is a TEM of a bacterium undergoing binary fission (septum visible)?
D
In E. coli, is “genome replication takes 20–30 min in rich exponential conditions” true or false
False — the practice notes say genome replication is always ~40–60 min, even if cells can double faster than that.
If the cell doubling time is faster than the time needed to replicate the chromosome, how can that still happen conceptually?
The cell can start a new round of replication before the previous one finishes (overlapping replication cycles / multiple forks) — so division can occur faster than a single full replication time.