Transcript Cell Membrane

Cell Membrane
Structure and Function
Function of the Cell Membrane
The cell membrane has a number of important
functions, it:
• separates the cell interior (protoplasm) from its
external environment (extracellular fluid – ECF)
• acts as a selective barrier to control the
movement of material into and out of the cell
• plays a role in cell behavior and the organization
of cells within tissues.
Cell Membrane Structure
• The structure (chemical composition) of
the cell membrane determines function
• The cell membrane is a dynamic fluid
structure capable of movement and
flexibility while the cell carries out cellular
functions.
Phospholipid Bilayer
• hydrophilic phosphate head and
hydrophobic tails of the fatty acids of a
phospholipid form a basic component of
the cell membrane
• The water soluble heads of a double layer
of phospholipids face the aqueous
cytoplasm and ECF while the hydrophobic
tails of the fatty acids face inward
Phospholipid Bilayer
Cholesterol
• Cholesterol molecules have several functions in
the membrane:
• animal cell membranes contain cholesterol
linking the fatty acids together and so stabilizing
and strengthening the membrane.
• They immobilize the first few hydrocarbon
groups of the phospholipid molecules making
the lipid bilayer less deformable and decreases
its permeability to small water-soluble molecules
Cholesterol in Cell Membrane
Protein Molecules
• integral proteins span from one side of
the phospholipid bilayer to the other
• peripheral proteins sit on one of the
surfaces
• Proteins comprise about 50% of the mass
of membranes, and are responsible for
most of the membrane's properties.
Internal Peripheral Proteins
• Protein inside surface of cell membranes
are often attached to the cytoskeleton and
are involved in maintaining the cell's
shape, or in cell motility. They may also be
enzymes, catalyzing reactions in the
cytoplasm.
External Peripheral Proteins
• Proteins on the outside surface of cell
membranes can act as receptors by
having a specific binding site where
hormones or other chemicals can bind.
This binding then triggers other events in
the cell.
• They may also be involved in cell signaling
and cell recognition, or they may be
enzymes, such as maltase in the small
intestine (more in digestion).
Carbohydrates
• Carbohydrates are found on the outer
surface of all eukaryotic cell membranes,
and are attached to the membrane
proteins or sometimes to the
phospholipids.
• Proteins with carbohydrates attached are
called glycoproteins, while phospholipids
with carbohydrates attached are called
glycolipids.
• The carbohydrates are short
polysaccharides composed of a variety of
different monosaccharides, and form a cell
coat or glycocalyx outside the cell
membrane. The glycocalyx is involved in
protection and cell recognition, and
antigens such as the ABO antigens on
blood cells are usually cell-surface
glycoproteins.
Fluid Mosaic Model of Cell
Membrane
Liposomes
• Liposomes are artificial lipid vesicles that
function like cell membranes because they
can fuse with a cell membrane and deliver
their contents directly into the cell
• They are used to deliver cancer fighting
drugs to specific cells reducing side effects
• They may also be a tool in delivering DNA
to cells as part of gene therapy
Liposome