Cells are separated from the external world by a thin, fragile structure called the plasma membrane that is only 5 to 10 nm wide. Here we present a brief description of the Plasma Membrane structure. We also discussed different membrane lipids & proteins. Please join us on Facebook- https://lnkd.in/fs_menC

1. PLASMA MEMBRANE STRUCTURE
Cells are separated from the external world by a thin, fragile structure called the plasma
membrane that is only 5 to 10 nm wide. Ernst Overton discovered that the dissolving power of
the outer boundary layer of the cell matched that of a fatty oil in 1890s.
Emergence of Lipid Bilayer- Dutch scientists, E. Gorter and F.
Grendel in 1925 first proposed that cellular membranes might
contain a lipid bilayer. They also suggested that the polar groups of
each molecular layer (or leaflet) were directed outward toward the
aqueous environment.
The Davson and Danielli model with backup from Robertson:
Physiologist Hugh Davson and biologist James Danielli first suggested that membranes have
proteins. In 1935, Davson and Danielli proposed that biological membranes are made up of
lipid bi-layers that are coated on both sides with thin sheets of protein.
Emergence of fluid mosaic model:
In 1972 the Fluid—Mosaic Membrane Model of membrane structure was proposed based on
thermodynamic principals of organization of membrane lipids and proteins and available
evidence of asymmetry and
lateral mobility within the
membrane matrix by S.
Jonathan Singer and Garth
Nicolson. The fluid mosaic
model describes the
structure of the plasma membrane as a mosaic of components —including phospholipids,
cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. For
comparison, human red blood cells, visible via light microscopy, are approximately 8 µm wide,
or approximately 1,000 times wider than a plasma membrane. The proportions of proteins,
lipids, and carbohydrates in the plasma membrane vary with cell type. For example, myelin
contains 18% protein and 76% lipid. The mitochondrial inner membrane contains 76% protein
and 24% lipid.
1. Integral proteins: Immersed in the bi-layer and held in place by the affinity of
hydrophobic parts of the protein for the hydrophobic tails of phospholipids on interior
of the layer.

2. 2. Peripheral proteins: More hydrophilic, and thus are non-covalently linked to the polar
heads of phospholipids and other hydrophilic
parts of other membrane proteins on the surface
of the membrane.
3. Lipid anchored proteins: Essentially
hydrophilic, so, are also located on the surface
of the membrane, and are covalently attached
to lipid molecules embedded in the layer.
Plasma Membrane Lipids:
The major lipids of the plasma membrane are phospholipids and phosphoglycerides.
Phospholipids are amphipathic molecules
that contain a charged (or polar)
hydrophilic head and two (nonpolar)
hydrophobic fatty acyl chains. The
amphipathic nature of the phospholipid
molecule is critical for the formation of the
bilayer: The hydrophobic fatty acyl chains
form the core of the bilayer, and the polar
head groups are exposed on the surface.
The sterol molecule cholesterol is also a critical component of the bilayer. It is found in both
leaflets and serves to stabilize the membrane at normal body temperature (37°C). A minor lipid
component of the plasma
membrane is glycolipids.
In addition, some regions of the
membrane contain lipids (e.g.,
sphingomyelin and cholesterol)
that aggregate into what are
called lipid rafts.
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