Biology Reference
In-Depth Information
(a)
(b)
pore
protein
lipid
bilayer
protein
FIGURE 8.1
The Danielli-Davson Pauci-Molecular model. (a) shows the original model consisting of a lipid
bilayer with globular proteins covering the surface. (b) shows a later revision of (a) with a trans-membrane peptide
pore.
would prevent favorable interactions between the phospholipid head groups and water.
While the Danielli-Davson Pauci-Molecular membrane model was a good start, and crucial
parts of the model, particularly the lipid bilayer, are still invoked today, significant alterations
were needed.
C. THE ROBERTSON UNIT MEMBRANE MODEL
In a 1957 meeting of the American Physiological Society, J. David Robertson proposed
a slight modification of the Danielli-Davson model membrane
[5,6]
. He called his model
the Unit Membrane model. Robertson was generally regarded as the premier electron micros-
copist of cell membranes and electron micrographs formed the basis of his model. Upon
staining membranes with KMnO
4
, Robertson always observed what is often referred to as
'railroad tracks', two dark bands separated by a light band (
Figure 8.2
,
[7]
). Robertson
defined the Unit Membrane as 'measuring ~75
˚
across, consisting of two parallel dense lines
FIGURE 8.2
A typical electron micrograph of a plasma membrane demonstrating the 'railroad tracks' on which
Robertson based his 'Unit Membrane' model
[7]
. The plasma membrane is observed to be two dark lines
surrounding a light interior.
