Prokaryotic Cell Wall and External Structures

Flashcards covering prokaryotic cell wall composition, Gram staining differences, Archaeal cell walls, external structures like flagella and pili, and the formation of endospores.

Peptidoglycan

A macromolecular network of the bacterial cell wall consisting of a repeating disaccharide attached by polypeptides to form a lattice.

$N$-acetylglucosamine (NAG)

One of the two monosaccharides that make up the disaccharide backbone of peptidoglycan.

$N$-acetylmuramic acid (NAM)

A monosaccharide in the peptidoglycan backbone to which tetrapeptide side chains are attached.

Tetrapeptide Side Chains

Polypeptide chains consisting of four amino acids in alternating $D$ and $L$ forms that link the peptidoglycan backbone.

Peptide Cross-bridge

A short chain of amino acids that may cross-link parallel tetrapeptides in peptidoglycan.

Gram Positive Bacteria

Bacteria that stain purple with the Gram stain because they possess a cell wall consisting of many layers of peptidoglycan.

Gram Negative Bacteria

Bacteria that stain red or pink with the Gram stain because they have a thin peptidoglycan layer and an outer membrane.

Teichoic Acids

Polymers of sugar alcohol (glycerol or ribitol) and phosphate found in Gram-positive cell walls that provide antigenic specificity.

Lipoteichoic Acids

Teichoic acids that span the peptidoglycan layer and are linked to the plasma membrane in Gram-positive bacteria.

Outer Membrane

A lipid bilayer in Gram-negative bacteria consisting of lipopolysaccharides ($LPS$), lipoproteins, and phospholipids; it protects against phagocytosis and antibiotics.

Periplasmic Space

The area between the outer membrane and the cytoplasmic membrane in Gram-negative bacteria containing degradative enzymes and transport proteins.

Porins

Proteins in the outer membrane of Gram-negative bacteria that form channels to allow the passage of molecules typically between $600-700$ daltons.

Lipopolysaccharide ($LPS$)

An endotoxin found in Gram-negative bacteria composed of Lipid A, a core polysaccharide, and an $O$ side chain ($O$ antigen).

Lipid A

The innermost portion of the $LPS$ that anchors it to the outer membrane and functions as an endotoxin.

Braun's Lipoprotein

The most abundant membrane protein in Gram-negative bacteria that covalently joins the peptidoglycan to the outer membrane.

Mycoplasma

A genus of bacteria that naturally lack a cell wall and contain sterols in their plasma membranes for added strength.

Acid-Fast Bacteria

Bacteria like Mycobacterium species that have a cell wall with a very high lipid content ($60$ of dry weight), including mycolic acid.

Pseudopeptidoglycan (Pseudomurein)

A substance found in some Archaeal cell walls that contains $N$-acetyltalosaminuronic acid and $\beta(1-3)$ glycosidic bonds.

S-layer

A regularly structured layer of protein or glycoprotein common in Archaea that may be the only structure outside the plasma membrane.

Osmotic Lysis

The swelling and bursting of a cell due to the movement of water into the cell when placed in a hypotonic solution.

Plasmolysis

The shriveling of the cytoplasm away from the cell wall when a cell is placed in a hypertonic solution.

Protoplast

A bacterial cell that has completely lost its cell wall.

Capsule

An organized, condensed layer of polysaccharides or proteins outside the cell wall that is not easily removed and protects against phagocytosis.

Slime Layer

A diffuse, unorganized layer of material outside the cell wall that is easily removed.

Fimbriae

Short, thin, hairlike proteinaceous appendages (up to $1000/cell$) that mediate attachment to surfaces.

Sex Pili

Longer and thicker appendages (typically $1-10/cell$) required for bacterial conjugation.

Flagellin

The protein that composes the filament of the bacterial flagellum.

Monotrichous

A flagellar arrangement consisting of a single flagellum at one end of the cell.

Peritrichous

A flagellar arrangement where flagella are spread over the entire surface of the cell.

Chemotaxis

The movement of a cell toward a chemical attractant or away from a chemical repellent.

Endospore

A dormant, highly resistant structure formed by some bacteria to survive harsh environmental conditions like heat, radiation, and desiccation.

Sporulation (Sporogenesis)

The complex multistage process of endospore formation that commences when growth ceases due to lack of nutrients.

Dipicolinic Acid

A substance complexed with calcium found in endospores that contributes to their high resistance.

Germination

The transformation of a dormant endospore back into a vegetative cell.