Bacterial Plasmids & Cell Envelope Vocabulary

Vocabulary flashcards covering plasmids, antibiotic resistance, and the structural components of Gram-positive and Gram-negative bacterial cell envelopes.

Plasmid

A small, circular piece of extrachromosomal DNA in bacteria or yeast that replicates independently of the chromosome.

Extrachromosomal DNA

Genetic material located outside the bacterial chromosome, often in the form of plasmids.

Nonessential Genetic Element

DNA that is not required for survival under ideal growth conditions but can confer advantages, such as plasmids.

R Plasmid

A resistance plasmid carrying genes that provide bacteria with antibiotic resistance.

Horizontal Gene Transfer

Movement of genetic material between organisms other than by descent, enabling bacteria to acquire plasmids from their environment or other cells.

Transformation

A form of horizontal gene transfer in which bacteria uptake free DNA (e.g., plasmids) from their surroundings.

Superbug

A bacterium that has acquired resistance to multiple antibiotics, often through R plasmids.

Cell Envelope

All layers surrounding a bacterial cell, including the cell wall and any outer membrane; must be external yet anchored to the cell.

Cell Wall

Rigid layer composed primarily of peptidoglycan that provides shape and protection to bacteria.

Peptidoglycan

Polymer of sugars and short peptides forming the main structural component of bacterial cell walls.

N-acetylglucosamine (NAG)

One of the alternating sugar units in peptidoglycan; largely structural.

N-acetylmuramic Acid (NAM)

The peptidoglycan sugar that carries a tetrapeptide side chain enabling cross-linking.

Tetrapeptide

Four-amino-acid chain attached to NAM that participates in cross-linking the cell wall.

Peptide Interbridge

Enzymatically created link between tetrapeptides, providing strength to the peptidoglycan mesh.

Gram-Positive Bacteria

Bacteria with a thick peptidoglycan layer (≈30+ layers) and no outer membrane; stain purple in Gram stain.

Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer (≈7–10 layers) plus an outer membrane containing LPS; stain pink/red in Gram stain.

Teichoic Acid

Polymer embedded in Gram-positive peptidoglycan that anchors the wall to the membrane and serves as a diagnostic marker.

Periplasmic Space

Region between inner membrane and outer membrane in Gram-negative bacteria that houses the thin peptidoglycan and enzymes.

Outer Membrane

External lipid bilayer of Gram-negative bacteria; its outer leaflet contains lipopolysaccharide.

Lipopolysaccharide (LPS)

Complex molecule in the outer leaflet of Gram-negative outer membranes, composed of O antigen, core polysaccharide, and Lipid A.

O Antigen

Highly variable outermost polysaccharide portion of LPS used to serotype Gram-negative strains (e.g., E. coli O157).

Core Polysaccharide

Central sugar region of LPS that links O antigen to Lipid A; less variable, sometimes species-specific.

Lipid A

Membrane-anchored lipid portion of LPS responsible for endotoxin activity and strong immune reactions.

Endotoxin

Toxic component of the bacterial cell envelope (primarily Lipid A) that triggers severe immune responses when released.

Broad-Spectrum Antibiotic

Drug effective against both Gram-positive and Gram-negative bacteria; defined by its wide range of activity.

Penicillin (β-lactam)

Antibiotic that targets peptide interbridges in peptidoglycan; highly effective against Gram-positives but less so against Gram-negatives.