Ch2: Microbial Cell Structure and Function

lt3

cytoplasmic membrane

layer that surrounds the cytoplasma, separates from environment, barrier

phospholipid bilayer

– fatty acids (hydrophobic, point inward)
– ester linkages in phospholipids
– glycerol + phosphate (hydrophilic, point outward)

catabolism

energy conservation

gram positive wall

Thick peptidoglycan (up to 90%), teichoic acids bind cations, lipoteichoic acids link to membrane.

gram negative wall

Thin peptidoglycan, outer membrane with LPS (lipid A = endotoxin), porins, periplasm.

Peptidoglycan

a vital polymer forming the mesh-like bacterial cell wall, providing structural support, maintaining cell shape, and protecting against osmotic lysis

pseudomurein

a structural polymer forming the cell walls of certain methanogenic archaea, functioning like bacterial murein (peptidoglycan) but with key chemical differences

Periplasm

space located between cytoplasmic and outer membrane

Outer membrane

a unique, asymmetric lipid bilayer providing a protective barrier against toxins and antibiotics, made of phospholipids (inner leaflet), lipopolysaccharides (LPS) (outer leaflet), lipoproteins, and porin proteins that control hydrophilic molecule entry

S-layers

Protein/glycoprotein crystalline sheets, outermost layer in many prokaryotes. Functions: sieve, attachment, protection, strength in Archaea.

Capsules/slime layers

Polysaccharide coats; roles in attachment, biofilms, virulence (anti-phagocytosis), dehydration protection.

Fimbriae

Short, numerous; adhesion.

Pili

Longer, fewer; conjugation (DNA transfer), type IV pili for twitching motility.

Hami

Archaeal grappling hooks for biofilm attachment

endospores

Highly differentiated cells resistant to heat, harsh chemicals, radiation, a resistant asexual spore that develops inside some bacteria cells

Twitching

Type IV pili extend/retract, ATP-driven.

Gliding

bacteria only, Smooth, pmf-driven, helical protein structures.

taxis

directed movement in response to chemical or physical gradients