Polysaccharide chains Polysaccharide chainsNH
CONHNHCONHCOCONH NHNH
CO NHNH
COCONHCO NHCOCONAGNAG NAG
NAGNAG NAGNAMNAM NAM NAMNAM NAMCONH
CONH
CONHNHCOCONH
COAmide (peptide
bond) cross linksTetrapeptide
chainsNAMNAM NAM NAMNAG NAG
NAGNAG NAG
NAGNAM NAMPentaglycine
cross linksTetrapeptide
chains(a) (b)
Figure A2.3 A schematic representation of the structure of the peptidoglycans of (a) Gram-
positive and (b) Gram-negative bacteriaOOOOOOOGlucose X Glucose XOOGlucose XXXOXO POO−O P OOO−O O−
−O P OOO−O POO−(a)(b)P OO O
O OOO−O P OOO−O P OOO−O POO PNAGNH 3 NH 3COCHCH 3 COCHCH 3ONAGO OCH 2 OHCHOHCH 2 OHGlycerol A glycerol
residue+ An alanine +
residueRibitolCH 2 OHCHOHCHOHCHOHCH 2 OH X is either H or an
alanine residueA ribitol
residueFigure A2.4 (a) A glycerol based teichoic acid. (b) A ribitol based teichoic acid. In many teichoic
acids the monosaccharide residues are glucose and N-acetylglucosamineThe exterior surface of Gram-negative bacteria is more complex than that
of the Gram-positive bacteria. It is coated with lipopolysaccharides, which
largely consist of long chains of repeating oligosaccharide units that are
attached to the outer membrane by a core oligosaccharide (Figure A2.5).
242 APPENDIX 2 BACTERIA