Plasma Membrane
Composition
Proteins (60%0
Lipids (40%)
Carbohydrates (1%)
Plasma Membrane
Models to explain the structure of plasma membrane
 Charles Overton (1895)
 Irving Langmuir (1917)
 E. Gorter and F. Grendel (1925)
 Hugh Davson and James Danielli (1935)
 Singer and Nicolson (1972)
Charles Overton (1895)
Membranes are made up of lipids
Irving Langmuir (1917)
Membranes are made up of phospholipids
Gorter and Grendel (1925)
Membrane is actually phospholipid bilayer
Daveson and Danielli (1935)
Phospholipid bilayer between two layers of globular
proteins
Sandwich Model
Problems
1. All membranes of the cell are identical
2. Placement of proteins: Proteins are amphipathic, if they
are layered on surface of membrane, their hydrophobic
parts would be in an aqueous environment.
Davson-Danielli Model
Singer and Nicolson (1972)
Proteins are dispersed and individually inserted into
phospholipid bilayer, with only their hydrophilic regions
protruding far enough from the bilayer to be exposed to
water.
Fluid Mosaic Model
Fluid Mosaic Model
Plasma Membrane
Composition
Proteins (60%0
Lipids (40%)
Carbohydrates (1%)
Lipids – lacithin and cholestrol
Carbohydrates are distributed between lipids and
proteins
Permeability of membrane
 Hydrophobic core of the membrane impedes the
transport of ions and polar molecules, which are
hydrophilic
 Hydrophobic molecules (CO2,
membrane and cross it with ease.
O2)
dissolve
in
 Very small molecules that are polar but uncharged can
pass through membrane rapidly (water, ethanol)
 Lipid bilayer is not permeable to large, uncharged polar
molecules (glucose and other sugars)
 Impermeable to all ions, even small ones (H+, Na+)