MicrobiologyStructure Function

Biol 370 – Campbell

9/18/13

Cell Wall

• Peptidoglycan

What does the name tell you about the chemical natureof the cell wall?

Differences Between Gram-Positiveand Gram-Negative Bacterial Cell

Walls

• Gram-Negative– One layer– Direct connections

• Gram-Positive– Multilayer– Polyglycine interbridges– Teichoic and lipoteichoic acids

Gram-Positive envelopes

• Capsule (not all species)– Polysaccharide

• S Layer (not all species)– Made of protein

• Thick cell wall– 9-amino acid crosslinks in

peptidoglycan– Teichoic acids for strength

• Thin periplasm

• Plasma membrane

The Gram-Positive Envelope

• Capsule (not all species)– Polysaccharide

• Outer Membrane– Lipopolysaccharide

• In outer leaflet only

• Thin cell wall– 4-amino acid crosslinks

in peptidoglycan

• Thick periplasm

• Plasma membrane

The Gram-Negative Envelope

PorinsCylinder of beta-sheets

Transport of sugars and peptides

Lipopolysaccharide (LPS)

-N may be as many as 200!-Help bacteria resist phagocytosis by white blood cells

Lipid-A Portion of LPS

• Medical importance

• Acts as an endotoxin– Only when released from lysed cell

• Over stimulates host defenses– May induce lethal endotoxic shock