Bacterial Outer Membranes and Cell Surface Structures

Vocabulary flashcards covering the components, structures, and functions of bacterial outer membranes, surface layers, and cell surface appendages.

Outer Membrane

A second lipid bilayer external to the cell wall in gram-negative organisms, containing phospholipids, proteins, and lipopolysaccharides.

Lipopolysaccharide (LPS)

A complex molecule composed of an O-specific polysaccharide, core polysaccharide, and Lipid A, which replaces most phospholipids in the outer half of the outer membrane in gram-negative bacteria.

Lipid A

The lipid component of lipopolysaccharide (LPS) that acts as an endotoxin and is toxic to animals.

Virulence Factor

A substance that enhances a pathogen's invasiveness and host damage.

Porins

Transmembrane proteins that function as channels, allowing the outer membrane to be relatively permeable to small molecules.

Braun Lipoprotein

A lipoprotein that anchors the bacterial outer membrane to the peptidoglycan cell wall.

Periplasm

A $15\,\text{nm}$ space located between the outer surface of the plasma membrane and the inner surface of the outer membrane where extracellular proteins function.

S-Layer

A rigid, but permeable, paracrystalline monolayer composed of interlocking protein or glycoprotein molecules, forming the outermost layer of the cell envelope in many Bacteria and almost all Archaea.

Capsule

A polysaccharide layer organized into a tight matrix that excludes small particles and is tightly attached to the cell surface.

Slime Layer

A loosely attached polysaccharide coat on the surface of the cell that is easily deformed and does not exclude particles.

Pili

Filamentous protein structures extending from the cell surface that enable attachment, pellicle or biofilm formation, genetic exchange, and motility.

Fimbriae

Short pili that mediate attachment, present in all gram-negative and most gram-positive bacteria.

Hamus

An attachment structure resembling a hook found in some Archaea that enables cells to attach to each other and surfaces.