Bacterial External Structures and Cell Walls

A collection of vocabulary flashcards covering the external structures, cell envelope, and cell wall variations of bacteria and archaea as described in the lecture notes.

Fimbria

Fine, proteinaceous, hairlike bristles from the cell surface that function in adhesion to other cells and surfaces.

Pili

Structures involved in motility (gliding and twitching motility) and the transfer of DNA from one cell to another; found only in Gram negative cells.

Conjugation pili

Specific pili used to transfer DNA from one cell to another.

Glycocalyx

A gelatinous polysaccharide and/or polypeptide covering that can appear as a capsule, slime layer, or extracellular polysaccharide (glycoprotein).

Capsule

A neatly organized glycocalyx that prevents phagocytosis, enables adherence to surfaces, and prevents desiccation.

Slime layer

A glycocalyx that is unorganized and loose.

Cell Wall

A bacterial structure that prevents osmotic lysis, protects the cell membrane, and provides shape; made of peptidoglycan in bacteria.

Peptidoglycan

A component of bacterial cell walls consisting of $2$ alternating amino sugars, $N$-acetyl-glucosamine ($NAG$) and $N$-acetyl-muramic acid ($NAM$), and $3$ or $4$ amino acids.

Teichoic acids

Components of Gram-Positive cell walls that may regulate payment of cations and provide antigenic specificity, making up $50\%$ of the cell wall weight.

Lipoteichoic acid

A type of teichoic acid in Gram-Positive cell walls that links to the plasma membrane.

Wall teichoic acid

A type of teichoic acid in Gram-Positive cell walls that links to peptidoglycan.

Lipopolysaccharide ($LPS$)

An endotoxin found in the outer membrane of Gram-negative cell walls composed of lipid A, core polysaccharide, and O-side chain.

Lipid A

The endotoxin portion of the lipopolysaccharide ($LPS$) found in Gram-negative bacteria.

Porins

Proteins that form channels through the outer membrane of Gram-negative cell walls.

Periplasmic space

The space between the peptidoglycan and the cell membrane, also including the space between the peptidoglycan and the outer membrane in Gram-negative cells.

Acid-fast cell walls

Cell walls that contain a waxy lipid called mycolic acid bound to peptidoglycan; characteristic of Mycobacterium.

Mycoplasmas

Bacteria that lack cell walls and contain sterols in their plasma membrane.

Archaea

Organisms that are either wall-less or have walls made of pseudomurein, which lacks $NAM$ and $D$ amino acids.

Lysozyme

An enzyme that digests the disaccharide in peptidoglycan, disrupting cell walls.

Penicillin

An antibiotic that inhibits the formation of peptide bridges in peptidoglycan.

Protoplast

A wall-less cell derived from a Gram-positive ($Gram+$) bacterium after the cell wall is entirely removed by lysozyme.

Spheroplast

A cell derived from a Gram-negative ($Gram-$) bacterium after its cell wall is partially removed by lysozyme.

L forms

Wall-less cells that swell into irregular shapes and are susceptible to osmotic lysis.