The Cell Wall

Lipopolysaccharide (LPS) a.k.a. Endotoxin

Consists of polysaccharides and lipid A. Found in outer membrane of Gram-negative bacteria. An integral part of the cell wall and is not released until the cell walls of dead bacteria are broken down.

Outer Membrane

Found primarily in gram-negative bacteria. Forms the outer most layer of the cell wall and is attached to the peptidoglycan by a continuous layer of small lipoprotein molecules (proteins combined with lipids) Certain viruses can adhere to some of the receptors on this.

Periplasmic Space

Gap between the cell membrane and the cell wall. Contains the cell wall peptidoglycan, many digestive enzymes, and transport proteins that destroy potentially harmful substances and transport metabolites into the bacterial cytoplasm. Gram-negative

Teichoic acid

Gram-positive bacteria has this. Gram positive bacteria also has a thick, dense layer of peptidoglycan in the cell wall. This consists of glycerol, phosphates, and sugar alcohol ribitol.

Peptidoglycan

The rigid cell wall outside the cell membrane is composed of this Molecules of N-acetylmuramic alternate with Molecules of N-acetylmuramic acid. They are cross linked by tetrapeptides (chains of 4 amino acids.

Acid-Fast Bacteria

Thick cell wall but mostly lipids, not peptidoglycan. Lipids include mycolic acids and other waxes and glycolipids. No outer membrane. No periplasmic space. Rigid or flexible. Difficult to digest. Least sensitive to dyes Stain as gram-positive

Gram-Positive Bacteria

Thick layer of peptidoglycan. Has teichoic acid. No outer membrane. No periplasmic space. Always rigid. Digest to protoplasts (cell membrane but no cell wall) Most sensitive to dyes and antibiotics. Purple stain

Gram-Negative Bacteria

Thin layer of peptidoglycan. Lipopolysaccharide as lipids. Has outer membrane. Has periplasmic space. Rigid or flexible. Digests to spheroplast (cell with cell membrane and most of the outer membrane) Moderately sensitive to dye. Does not retain purple stain

Mycoplasma

no cell walls. protected by sterols (strengthened cell membrane) Typical in eukaryotes

L-forms

normally have cell walls but suddenly lose their ability to form walls

Porins

proteins that form channels through the outer membrane

Stereoisomers

structures that are mirror images if each other amino acids have this

Diaminopimelic

the third amino acid in gram-negative

Lysine

the third amino acid in gram-positive