Gram-Positive Cell Wall

•        Outer boundary of the cell; one of the most important parts of a Procaryotic cell

•         Most bacteria have strong walls that give them shape and protect them from osmotic lysis (Exception- mycoplasmas and some Archaea) 

•        Wall shape and strength is primarily due to peptidoglycan

•        The cell walls of many pathogens contribute to their pathogenicity

•         The wall can protect a cell from toxic substances and is the site of action of several antibiotics

Peptidoglycan or Murein

•        polymer composed of identical subunits

•        alternating sugar derivatives-

•         N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)

•        Connected to the carboxyl group of N-acetylmuramic acid is a peptide chain of 4 alternating D- and L-amino acids (D-glutamic acid, L/D-alanine, diaminopimelic acid (not found in proteins) etc. (L-lysine, in some)

•        The presence of D-amino acids protects against attack by most peptidases

•        Chains of linked peptidoglycan subunits are joined by cross- links between the peptides

•        Cross-linking results in a dense, interconnected network of peptidoglycan

•        strong enough - retain the shape and integrity

•        elastic and stretchable

•        porous, for molecules to penetrate

Gram-Positive Cell Walls

•        Thick, homogeneous cell wall of gram-positive bacteria composed primarily of peptidoglycan

•        Contain large amounts of teichoic acids (polymers of glycerol or ribitol joined by phosphate groups)

                                                Gram-Positive Cell Wall

•        Teichoic acids - connected by a covalent bond to N-acetylmuramic acid of the peptidoglycan or to plasma membrane lipids (lipoteichoic acids)

•   Teichoic acids extend to the surface of the peptidoglycan-negatively charged- give the gram-positive cell wall its negative charge.

•    Important in maintaining the structure of the wall.

•        Teichoic acids - not present in gram-negative bacteria.