Phospholipids are a
class of lipids and are
a major component
of all biological
membranes. They
produce tiny pores
which can allow
simple diffusion and
osmosis.
The ion channel on
which the ligand is
bound, opens or
closes in response to
the signals from the
ligand.
Cholesterol helps to “pack”
phospholipids into the membranes,
which gives more rigidity to the
membranes. Cholesterol also
serves other useful functions in the
membrane, such as
Integral proteins act
as a transporter for
various molecules
that otherwise
wouldn’t be able to
move across the
membrane. The
identification of the
cell for recognition of
other cells is another
function that the
integral proteins
serve.
The ion channel
opens and closes in
order to let ions pass
through.
A model called the Fluid Mosaic Model has been created as the detailed
structure of the membrane is too fine to see even with an electron
microscope.
The Fluid Mosaic Model is called because:
Fluid – the molecules are always changing position with each other
Mosaic – the pattern of proteins looks like a mosaic
The membrane acts as a
boundary layer to contain the
cytoplasm
The membrane
provides a stable
site for the
binding and
catalysis of
enzymes
Functions of the plasma membrane
Some of the transport
processes of the membrane
happen automatically, these are
passive transport processes.
Others require energy from the
cell, these are active transport
processes
The membrane helps
to protect the cell
The membrane is
selectively
permeable, it can
select the
chemicals which
pass in and out
of the cell
The interlocking
surfaces of the
membrane bind the
cell together
Cholesterol
makes the
membrane
more rigid
which gives
greater
protection to
the cell.
How the structure of the plasma
membrane helps it to function
The tiny pores created by
phospholipids allow the
cell to perform processes
such as osmosis and
diffusion
The proteins in
the membrane
help to provide a
stable site for
the binding and
catalysis of
enzymes