Microbiology (WK3): Cell Division, Envelope Structure, Endospores, Motility, and Microscopy

Vocabulary flashcards covering bacterial division mechanics, peptidoglycan cell wall architectures, Gram and differential staining principles, endospore biology, gas vesicles, cell envelope appendages, flagellar motility, and electron microscopy techniques.

Binary Fission

The predominant bacterial replication mechanism in which a single cell elongates, copies its circular chromosome, forms a central division septum guided by FtsZ assembly, and splits into two daughter cells.

Peptidoglycan (Murein)

A meshlike cell wall polymer unique to bacteria composed of long alternating chains of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by peptide bridges.

Topoisomerase IV

The essential decatenating enzyme that resolves topological entanglement by cutting apart the two interlocked circular chromosomes remaining after replication forks meet.

Double Adder Model

The cell cycle rule established in 2019 demonstrating that chromosome initiation and cell division are each triggered by a fixed added volume since the last initiation event, rejecting the 1968 Donachie initiation mass model.

Multifork Replication

A cell cycle mechanism in rapidly growing Escherichia coli where new rounds of replication initiate at oriC before the previous round has finished, leading to overlapping replication cycles.

Nucleoid

The concentrated, non-membrane-bound cytoplasmic region occupied by the highly compacted and organized bacterial chromosome.

ParABS System

A chromosome partitioning system where ParB binds parS DNA sites and interacts with the ATPase ParA to actively position replicated DNA domains toward opposite cell poles.

FtsZ

A tubulin-homologous cytoskeletal protein that polymerizes at midcell into a dynamic Z ring anchored by FtsA and ZipA to define the division plane and coordinate septum formation.

Divisome

The macromolecular protein complex recruited to the Z ring that includes peptidoglycan synthases (such as FtsW and FtsI) to build the dividing cell septum.

Nucleoid Occlusion

A spatial regulation mechanism using proteins such as SlmA in Escherichia coli or Noc in Bacillus subtilis to inhibit FtsZ ring assembly over unsegregated DNA.

Min System

A spatial control mechanism in which MinC, MinD, and MinE act together to inhibit FtsZ Z-ring formation near the cell poles.

Monoderm

A bacterial cell envelope architecture featuring a single cytoplasmic membrane surrounded by an inner wall zone and a thick layer of peptidoglycan embedded with teichoic acids.

Diderm

A bacterial cell envelope architecture consisting of an inner plasma membrane, a gel-filled periplasmic space containing a thin peptidoglycan layer ($4\,nm$ or less), and an outer membrane carrying lipopolysaccharide.

Atypical Diderm

An envelope architecture found in Mycobacteriaceae comprising an inner membrane, a peptidoglycan-arabinogalactan layer, and an outer mycomembrane composed of waxy mycolic acids.

Lipopolysaccharide (LPS)

An asymmetric glycolipid forming the outer face of Gram-negative outer membranes, composed of a variable O antigen, a core polysaccharide, and an anchored Lipid A endotoxin.

Lipid A

The hydrophobic membrane anchor of lipopolysaccharide containing six acyl chains in its active state; functions as an endotoxin recognized by the host TLR4 receptor.

Capsule

An organized, tightly bound outer glycocalyx layer composed of polysaccharides or proteins that aids in surface adhesion, prevents desiccation, and evades host phagocytosis.

Slime Layer

A loosely attached, unorganized glycocalyx layer made of polysaccharides, glycoproteins, or glycolipids that can be easily washed off and assists in biofilm formation.

S-layer

A crystalline monolayer structure composed of self-assembling proteins or glycoproteins that sits outside the cell wall in bacteria or acts as the primary cell wall in many archaea.

Gram's Iodine

A mordant in Gram staining that performs an anion swap, exchanging chloride for iodide to form an insoluble crystal violet–iodide precipitate within the peptidoglycan mesh.

Endospore

A highly resistant, dormant structure produced within certain Gram-positive bacteria (e.g., Bacillus and Clostridium) to protect the cell genome under starvation or environmental stress.

Forespore

The early internal structure created during sporulation when an asymmetric septum forms and the mother cell engulfs the smaller DNA compartment with a double membrane.

Spore Cortex

A thick, loosely cross-linked (~4% peptide cross-links) peptidoglycan layer synthesized between the inner and outer membranes surrounding the forespore.

Small Acid-Soluble Proteins (SASPs)

Spore core proteins that bind and saturate DNA, altering UV radiation damage from cyclobutane pyrimidine dimers to the error-free repairable spore photoproduct.

Germinants

Specific small nutrient molecules recognized by receptors in the spore's inner membrane that trigger commitment to germination and resumption of active growth.

Gas Vesicle

A rigid, hollow protein shell composed of GvpA ribs and GvpC cross-links that is permeable to atmospheric gas but excludes liquid water, providing cellular buoyancy.

Pseudomurein

An archaeal cell wall polymer containing N-acetyltalosaminuronic acid instead of NAM and $\beta\text{-1,3}$ glycosidic linkages that render it resistant to lysozyme and penicillin.

Bacterioruberin

A carotenoid pigment synthesized from isoprenoid precursors that gives haloarchaeal populations in high-salinity salt flats their characteristic pink color.

Fimbriae

Short, bristle-like protein appendages projecting from the bacterial cell surface by the hundreds that enable attachment to surfaces and host cells.

Sex Pilus (F Pilus)

A specialized, elongated surface protein appendage involved in bacterial conjugation and horizontal transfer of DNA between cells.

Flagellin

The structural protein subunit that polymerizes to form the hollow, helical filament of a bacterial flagellum.

Proton Motive Force

The electrochemical proton gradient across the plasma membrane that flows through stator proteins to power the mechanical rotation of the flagellar basal body motor.

Flagella Arrangements

Patterns of bacterial flagellar placement categorized as monotrichous (single polar flagellum), lophotrichous (tuft at one end), amphitrichous (flagella at both ends), or peritrichous (flagella covering the entire surface).

Run

Smooth forward swimming motion in peritrichously flagellated bacteria generated when flagella rotate counterclockwise and bundle together into a single propeller.

Tumble

Brief, random reorientation of a peritrichously flagellated bacterium caused by clockwise flagellar rotation that splays the bundle apart and prevents forward movement.

Chemotaxis

Directional swimming toward chemical attractants or away from repellents achieved by modulating tumble frequency rather than active steering.

Archaellum

The rotating archaeal motility organelle driven by ATP hydrolysis, which is assembled from the base and structurally homologous to bacterial type IV pili.

Transmission Electron Microscope (TEM)

An electron microscope that passes an electron beam through ultrathin ($20\text{--}100\,nm$) plastic-embedded sections stained with heavy metals to image internal subcellular fine structure.

Scanning Electron Microscope (SEM)

An electron microscope that scans the surface of a dried, sputter-coated specimen with an electron beam to produce highly detailed three-dimensional surface images.

Mesosome

A historic textbook artifact once described as a functional plasma membrane infolding, later proven to be manufactured by chemical fixatives used in electron microscopy preparation.

Cryo-Electron Microscopy (Cryo-EM)

A high-resolution imaging method in which samples are rapidly frozen into vitreous glass without chemical fixatives, dehydration, or heavy metal stains, preserving native cellular structure.