Prokaryotic Cell Exterior and Internal Components – Vocabulary Flashcards

A set of vocabulary flashcards covering outer membrane structure, capsules and slime layers, motility and chemotaxis, pili/fimbriae, genetic elements, ribosomes, cytoskeleton, storage inclusions, gas vesicles, and endospore formation.

Outer membrane

In Gram-negative bacteria, the outer membrane blocks passage of many molecules (including some antimicrobials) but contains porins that allow diffusion of small molecules.

Porins

Protein channels in the outer membrane that permit passage of small molecules into the periplasm.

Periplasm

Gel-like space between the cytoplasmic membrane and outer membrane in Gram-negative bacteria; contains binding proteins and transport systems.

Capsule

A distinct, gelatinous outer layer outside the cell wall that protects surfaces and aids adhesion; often helps evade host defenses.

Slime layer

A diffuse, irregular outer layer outside the cell wall that aids adhesion and biofilm formation.

Biofilm

Community of bacteria embedded in a slime matrix that adheres to surfaces.

Flagellum (Flagella)

Long, helical protein structures that enable motility by spinning like propellers.

Chemotaxis

Movement toward attractants (nutrients) or away from repellents (toxins) guided by chemical gradients; involves runs and tumbles.

Aerotaxis

Movement influenced by oxygen concentration.

Magnetotaxis

Movement guided by Earth’s magnetic field due to magnetic components in some bacteria.

Thermotaxis

Movement in response to temperature changes.

Phototaxis

Movement in response to light.

Pili

Short, thin filamentous projections; used for attachment and, in some cases, DNA transfer (sex pili). Pili are shorter/thinner than flagella.

Fimbriae

Very short, fine filaments that enable attachment to surfaces.

Plasmid

Small, circular DNA molecule separate from the chromosome; carries accessory genes (e.g., antibiotic resistance) and can be transferred between bacteria.

Chromosome

Single, circular double-stranded DNA molecule that carries essential genes in bacteria.

Nucleoid

Gel-like region in the cytoplasm where the bacterial chromosome is located; not membrane-bound.

70S ribosome

Prokaryotic ribosome composed of 30S and 50S subunits; smaller than eukaryotic ribosomes.

Cytoskeleton

Interior protein framework that helps maintain cell shape and is involved in cell division; bacterial cytoskeleton resembles the eukaryotic one in function.

Storage granules

Polymer inclusions that store nutrients (carbon and energy) and are not membrane-bound.

Gas vesicles

Protein-bound, gas-filled structures that provide buoyancy for some aquatic bacteria to optimize sunlight exposure.

Endospore

A dormant, highly resistant cell type formed by some bacteria (e.g., Bacillus, Clostridium) to withstand harsh conditions.

Sporulation

Process by which an endospore is formed inside the mother cell.

Forespore

The developing compartment that becomes the mature endospore during sporulation.

Spore coat

Protective protein layer surrounding the endospore.

Cortex

Peptidoglycan-rich layer between spore coat and core that contributes to resistance.

Core

The innermost, DNA-containing region of the endospore.

Mother cell

The original cell that engulfs the forespore and eventually degrades, releasing the mature endospore.

Germination

Process by which an endospore breaks dormancy and returns to vegetative growth.