Hydrophilic headgroup
of phospholipid
Hydrophobic fatty acyl
chains of phospholipid
Glycosylation may
occur in some instances
Outside of cell
Integral membrane proteins
Peripheral membrane proteins
Cytoplasm
Fig. 15. Fluid mosaic model of bacterial plasma membrane structure. The bilayer consists of two
phospholipid leaflets with their hydrophobic fatty acyl chains pointing inward and the hydrophilic
headgroups facing the aqueous environment. Integral membrane proteins are embedded in the
membrane through (normally -helical) hydrophobic segments whereas peripheral membrane proteins
have more hydrophilic surface character and are generally located at the membrane interface associated
with integral membrane proteins or phospholipid.
Fig. 16. Cartoon of the Gram-positive
cell envelope highlighting the covalent
attachment of teichoic acids to the
peptidoglycan layer and the anchoring of
lipoteichoic acids to the outer leaflet of the
plasma membrane. Depending on
circumstances (polymer chain
length, wall thickness, presence of capsules
etc) both teichoic acids and lipoteichoic
acids may be expressed on the cell surface
and (as in streptococci) be important
surface antigens. The presence of a defined
periplasmic space in Gram-positive bacteria
is somewhat controversial.
R = H, sugar, amino sugar or alanine (Ala)
n = 30-40
R1/2 = fatty acids
X = head group
EtN-P =
phosphoethanolamine
R1/2 = fatty acids
R = H or Ala
R1/2/3 = fatty acids
…..(of the murein tetrapeptide)
Generalized chemical structures of important bacterial envelope components.
1, Glycerol teichoic acid; 2, Ribitol teichoic acid; 3, Teichuronic acid based on (1-6)-linked
N-acetyl mannosaminuronic acid and glucose; 4, Phospholipid; 5, Lipoteichoic acid (LTA); 6, The Braun