The
Cell Membrane
All
cells are separated from the external environment by a Plasma
Membrane
It is composed of many components.
Phospholipids
Cholsterol
Proteins
Very
similar to triglycerides however, one of the fatty acid chains has been
replaced by a very polar Phosphate group

This
poses a problem for the molecule since the molecule is both polar and
non-polar simultaneously.
It
is therefore very unstable in water, polar end is attracted to it, non polar
tails are repelled by it.
This
forces the phospholipids to take an arrangement such that their tails face
each other. This accomplishes 2
things..
The
polar heads can be adjacent to polar water molecules
The
non-polar tails can be adjacent to each other.

As
the layer enlarges it forms a bubble shape formed of a lipid bilayer which is the foundation
of the plasma membrane


The
membrane requires a few more components to make it complete:
Cholesterol
Functions
to hold the membrane together like glue.
Adds strength to the membrane.
Proteins
(2 types)
Intrinsic
Proteins
Extend
into or through lipid bilayer
Often
are channel proteins allowing large
molecules in/out
Extrinsic
Proteins
Exist
only on surfaces of the bilayer
Often
serve as receptor molecules
Glycoproteins
serve as cellular markers (nametags)

Entire model is referred to as the Fluid Mosaic model of the plasma membrane
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