Visualizing Microbes: Prokaryotic Cell Anatomy and Staining Techniques

Vocabulary practice flashcards covering prokaryotic internal and external cell structures, osmotic environments, endospore biology, cell morphology and arrangements, and microbiological staining protocols.

Osmotic pressure

The pressure that occurs due to differences in the concentration of solutes on opposing sides of a semipermeable membrane.

Osmosis

The diffusion of water across a semipermeable membrane from an area with a lower solute concentration (more water) to an area with a higher solute concentration (less water) until concentrations balance.

Isotonic medium

An environment in which solute concentrations inside and outside the cell are approximately equal, resulting in no net movement of water across the cell membrane.

Hypertonic medium

An environment where the solute concentration outside the cell exceeds that inside the cell, causing water to diffuse out of the cell.

Hypotonic medium

An environment where the solute concentration inside the cell exceeds that outside the cell, causing water to diffuse inward and potentially leading the cell to lyse or burst.

Nucleoid

A condensed, lighter-staining region in prokaryotic cells where circular, haploid DNA is located without being enclosed by a nuclear membrane.

Nucleoid-associated proteins (NAPs)

Proteins that organize DNA within the prokaryotic nucleoid, functioning similarly to eukaryotic histones.

Plasmid

A small circular DNA molecule in prokaryotes that is separate from the chromosome and frequently carries advantageous genes, such as those encoding antibiotic resistance.

$70\text{S}$ ribosome

The prokaryotic cytoplasmic organelle responsible for protein synthesis, composed of proteins and rRNA and made up of a $30\text{S}$ small subunit and a $50\text{S}$ large subunit.

Inclusions

Cytoplasmic structures in prokaryotic cells used to store excess nutrients, including glycogen, starch, phosphate, and sulfur.

Volutin granules

Prokaryotic inclusions that store polymerized inorganic phosphate used in cellular metabolism and biofilm development.

Polyhydroxybutyrate (PHB)

A lipid inclusion enclosed by a phospholipid monolayer that serves as a nutrient store and has industrial applications in biodegradable bioplastics.

Vegetative cell

A metabolically active, growing bacterial cell that is sensitive to extreme temperatures and radiation.

Endospore

A dormant, dehydrated, and highly durable cellular structure that shields the bacterial genome against extreme temperatures, radiation, and harsh conditions.

Sporulation

The multistep process by which a vegetative bacterial cell transforms into a protective, dormant endospore following asymmetric cell division.

Basic stain

A staining dye containing positively charged chromophores (e.g., crystal violet, methylene blue, safranin) that binds to negatively charged cell molecules like nucleic acids and proteins.

Acidic stain

A staining dye with negatively charged chromophores (e.g., eosin, acid fuchsin, Congo red) that binds to positively charged cellular molecules and structures.

Negative stain

A staining method using dyes such as India ink or nigrosin that dyes the background while leaving the specimen unstained and bright.

Differential stain

A staining procedure using multiple dyes to distinguish between different types of organisms or cell components based on structural or chemical variations.

Mordant

A chemical agent, such as Gram's iodine, that sets or stabilizes dyes by creating an insoluble complex within cell walls.

Crystal violet

The positively charged primary stain in Gram staining that penetrates both Gram-positive and Gram-negative cells, imparting an initial purple color.

Gram's iodine

The mordant in Gram staining that binds with crystal violet to form a large crystal violet–iodine (CV-I) complex that remains trapped in thick peptidoglycan layers.

Decolorizer (Gram stain)

An alcohol or acetone/alcohol solution applied to wash away the crystal violet–iodine complex from thin-walled Gram-negative bacteria while leaving Gram-positive cells purple.

Safranin

The secondary counterstain in the Gram stain procedure that stains decolorized Gram-negative cells pink or red.

Gram-positive bacteria

Bacteria that possess a thick peptidoglycan cell wall containing teichoic acids, which retains crystal violet dye after alcohol decolorization, making them appear purple.

Gram-negative bacteria

Bacteria that feature a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide, which release crystal violet upon decolorization and counterstain pink/red with safranin.

Acid-fast stain

A differential stain using basic fuchsin and acid-alcohol decolorization that identifies acid-fast bacteria (such as M. tuberculosis) as red and non-acid-fast bacteria as blue.

Schaeffer-Fulton procedure

An endospore staining method using heat to drive malachite green into endospores (turning them bluish-green) followed by a safranin counterstain for the surrounding vegetative cell structures (pink/red).

Capsule stain

A diagnostic staining technique using negative background dyes (India ink or nigrosin) alongside a counterstain so that capsules appear as clear halos surrounding the colored cells.

Flagella stain

A staining procedure using a tannic acid or potassium alum mordant to coat and thicken bacterial flagella before applying pararosaline or basic fuchsin for visualization.

Coccus

A round or spherical prokaryotic cell shape

Bacillus

A rod-shaped prokaryotic cell shape

Vibrio

A curved rod prokaryotic cell shape

Coccobacillus

A short, oval-like rod prokaryotic cell shape

Spirillum

A rigid, spiral-shaped prokaryotic cell

Spirochete

A long, loose, helical spiral prokaryotic cell

Diplococcus

A prokaryotic cellular arrangement consisting of a pair of two cocci

Tetrad

A prokaryotic cellular arrangement consisting of four cocci arranged in a square grouping

Streptococcus

A prokaryotic cellular arrangement consisting of a chain of spherical cells

Staphylococcus

A prokaryotic cellular arrangement consisting of an irregular cluster of spherical cells

Diplobacillus

A prokaryotic cellular arrangement consisting of a pair of rod-shaped cells

Streptobacillus

A prokaryotic cellular arrangement consisting of a linear chain of rod-shaped cells

Palisade

A prokaryotic cellular arrangement characterized by V- or L-shaped formations or side-by-side groupings of rod-shaped cells