Gram-Positive vs Gram-Negative Cell Walls and Gram Stain Concepts

Vocabulary flashcards covering Gram-positive vs Gram-negative cell wall features and Gram staining concepts.

Peptidoglycan

Thick, mesh-like polymer forming the main structural layer of the Gram-positive cell wall; anchors with teichoic and lipoteichoic acids.

Gram-positive cell wall

Cell wall with a thick peptidoglycan layer and no outer membrane; contains teichoic and lipoteichoic acids.

Lipoteichoic acid

Teichoic acid anchored in the cell membrane and extending through the peptidoglycan layer; common in Gram-positive bacteria.

Teichoic acid

Polymers associated with the Gram-positive cell wall that contribute to charge and structure; can be wall-associated.

Outer membrane

An outer lipid bilayer present in Gram-negative bacteria that adds an extra barrier; absent in Gram-positive bacteria.

Gram-negative cell wall

Cell wall with a thin peptidoglycan layer plus an outer membrane; more complex permeability characteristics.

Crystal violet

Primary stain in Gram staining that penetrates cell walls and, with iodine, forms a dye–iodine complex to trap color.

Iodine (mordant)

Chemical that binds crystal violet to form a larger complex inside the cell, helping retention of stain.

Alcohol decolorizer

Solvent (ethanol or acetone–ethanol) used in Gram staining; decolorizes Gram-negative cells by dissolving outer membrane and thin peptidoglycan, while Gram-positive remain stained.

Transport proteins

Proteins in the cell membrane that facilitate the movement of substances into and out of the cell; present in Gram-positive membranes.

Thick peptidoglycan layer

Resulting in strong retention of the primary stain in Gram-positive bacteria during the Gram stain.

Gram stain outcome

Gram-positive appear purple; Gram-negative appear pink after completing the Gram stain due to decolorization differences.