Lip id
Leaflet
Hydrophilic Region
Pol ypeptide "
- - - - - - ,
• • •
•
Hydrophobic Region
.... ' .
Mucoprotein
• • •
•
Ins ide
•
• •
• •
Electron Dense
Electron Transparent
About
100.&
• • • •
•
Electron Dense
Outs ide
Fig. 1.2. Diagrammatic representation of the bimolecular lipid leaflet arrangement of the
plasma membrane according to the DAVSO N-DANIELLI-RoBERTSON model.
and was first described by]. D AVID ROBERTSON (1958 and 1964). ROBERTSON su ggested that the electron transparent area represented the hydrophobic chains of
the lipids, while th e dark border on either side consists of their hydrophilic 'heads',
to gether with a protein or pol ypeptide at the inner surface and a mu coprotein or
mucopolysaccharide on th e outside. This later hypoth esis deviates fro m the D AVSO N-DANIELL! model and w as sugg ested by differences in the appearance of each
border when 'f ixed ' in either osmic acid or potassium permanganate. This D AVSO ND ANIELLI-RoBERTSON model has gained widespread accep tance (but see th e repeating unit of GREEN and PERDUE, 1966) and is suppo rted by evidence obtained
by X-ray diffraction and optical birefringence techniques, as well as the behaviour
of lipid-protein-water mixtures in v itro.
The detailed relat ion ship of such a general mol ecul ar arr angement to th e diverse
special characteristics of various types of cells is not ye t clear. Thus, ho w do such
mol ecular. specific functions as facilitated diffusion , active transport and excitant -recepto r sites fit int o such a structure ? Unit membranes may contain numerous molecular sp ecies of proteins , phospholipids and cholesterol and it is conceivable that their characteristic properties reflect differences in their precise molecular
composition and arrangem ent . Such specific information on the structure of cell
membranes is not ye t available.
b) Capill aries
Th e capillaries constitute th e b arrier separating th e interstitial (or int ercellular) flu id
from the blood pl asma. They are tubular vessels rou ghly 102 mm in diameter with
walls about 103 mm wide and are connected at either end with art erioles and ve17
Leaflet
Hydrophilic Region
Pol ypeptide "
- - - - - - ,
• • •
•
Hydrophobic Region
.... ' .
Mucoprotein
• • •
•
Ins ide
•
• •
• •
Electron Dense
Electron Transparent
About
100.&
• • • •
•
Electron Dense
Outs ide
Fig. 1.2. Diagrammatic representation of the bimolecular lipid leaflet arrangement of the
plasma membrane according to the DAVSO N-DANIELLI-RoBERTSON model.
and was first described by]. D AVID ROBERTSON (1958 and 1964). ROBERTSON su ggested that the electron transparent area represented the hydrophobic chains of
the lipids, while th e dark border on either side consists of their hydrophilic 'heads',
to gether with a protein or pol ypeptide at the inner surface and a mu coprotein or
mucopolysaccharide on th e outside. This later hypoth esis deviates fro m the D AVSO N-DANIELL! model and w as sugg ested by differences in the appearance of each
border when 'f ixed ' in either osmic acid or potassium permanganate. This D AVSO ND ANIELLI-RoBERTSON model has gained widespread accep tance (but see th e repeating unit of GREEN and PERDUE, 1966) and is suppo rted by evidence obtained
by X-ray diffraction and optical birefringence techniques, as well as the behaviour
of lipid-protein-water mixtures in v itro.
The detailed relat ion ship of such a general mol ecul ar arr angement to th e diverse
special characteristics of various types of cells is not ye t clear. Thus, ho w do such
mol ecular. specific functions as facilitated diffusion , active transport and excitant -recepto r sites fit int o such a structure ? Unit membranes may contain numerous molecular sp ecies of proteins , phospholipids and cholesterol and it is conceivable that their characteristic properties reflect differences in their precise molecular
composition and arrangem ent . Such specific information on the structure of cell
membranes is not ye t available.
b) Capill aries
Th e capillaries constitute th e b arrier separating th e interstitial (or int ercellular) flu id
from the blood pl asma. They are tubular vessels rou ghly 102 mm in diameter with
walls about 103 mm wide and are connected at either end with art erioles and ve17